Sound and vibrations that cause the skull bone to vibrate can be heard as ordinary sounds and this is termed hearing by bone conduction (BC). Not all mechanisms that causes a skull vibration to result in BC hearing are known, and one such unknown is how the direction of the vibration influences BC hearing. This direction sensitivity was investigated by providing BC stimulation in five different directions at the vertex of the guinea pig skull. The hearing thresholds for BC stimulation was obtained in the frequency range of 2 to 20 kHz by measurements of compound action potential. During the stimulation by BC, the vibration of the cochlear promontory was measured with a three-dimensional laser Doppler vibrometer resulting in a set of unique three-dimensional velocity magnitude combinations for each threshold estimation. The sets of three-dimensional velocity magnitude at threshold were used to investigate nine different predictors of BC hearing based on cochlear promontory velocity magnitudes, six single direction , one linear combination of the three dimension velocity magnitudes, one square-rooted sum of the squared velocity magnitudes, and one sum of the weighted three dimensional velocity magnitudes based on a restricted minimum square error (MSE) estimation. The MSE gave the best predictions of the hearing threshold based on the cochlear promontory velocity magnitudes while using only a single direction gave the worst predictions of the hearing thresholds overall. According to the MSE estimation, at frequencies up to 8 kHz the vibration direction between the right and left side gave the greatest contribution to BC hearing in the guinea pig while at the highest frequencies measured, 16 and 20 kHz, the anteroposterior direction of the guinea pig head gave the greatest contribution. Early on, sound transmission by BC was assumed similar to the waves on a water surface, which means that the vibration is only in one direction, forming a transversal wave, perpendicular to the surface4. Later it was understood that when the wave propagated across the cranial vault, it comprised both longitudinal and transverse components and at low frequencies, the human skull behaves like a rigid body5. Since then, multiple studies have been conducted to investigate the mode of vibration in the skull during BC stimulation11.These studies have confirmed that the skull vibration is complex and frequency dependent during BC stimulation. Such complex motion prevents an easy transformation of the skull bone vibration to a sound perception. Consequently, at present, it is not known how different types of wave modes and vibration directions influence hearing by BC stimulation.The two main pathways of hearing, air conduction (AC) and bone conduction (BC), have been studied extensively during the last two centuries. When vibrations are transmitted in the skull bone, the hearing sensations by BC are perceived the same as with normal AC14. Hearing by BC involves several contributing pathways16. The BC stimulation can be either directly to the skull bone or on the skin over the skull, and transmitted as vibrations of the skull to the inner ear, through the ear canal and middle ear, or through the cerebrospinal fluid (CSF). Irrespective of pathway for the vibratory energy17, all integrate in the inner ear and cause a motion of the basilar membrane generating a hearing sensation18.For AC hearing, sound vibration propagates in the air, is collected by the external ear (pinnae) and is transmitted to the middle ear ossicular chain  via the eardrum and finally excites the fluids in the inner ear (cochlea) causing a motion of the basilar membrane to generate a hearing sensation20. For BC stimulation, neither the middle ear ossicles motion nor the round window motion can be used to assess the hearing excitation 21. Most studies that use vibration as a means to assess the BC excitation use the vibration magnitude of the cochlear promontory as an estimate of the hearing stimulation. The rationale is that the vibration magnitude of the bone around the inner ear seem to be a dominant pathway for BC hearing in the human15 and the cochlear promontory vibration magnitude correlates with perceived BC hearing9.For AC stimulation, the motion of the stapes is often used as an approximation of the hearing stimulation10. However, the bone around the cochlea vibrates in all three space dimensions, and it is currently not known for what direction or type of wave motion the inner ear is most sensitive. One approach to accommodate for this uncertainty is to use the square-root of the sum of the orthogonal vibration components squared5. The rationale for this estimate is that it represents the vibrational energy of the cochlear promontory and it is less affected by resonances or anti-resonances in the transmission pathway that can appear in a single direction. A third proposed estimate of the BC perception is to compute the main vibrational direction and use this maximum as a proxy of the BC sound22. One advantage of the latter is that it contains the phase information of the vibration which is important for understanding the mode of vibration.The most common estimate of BC perception based on cochlear promontory vibration is a one-dimensional motion, often obtained by a laser beam through the ear canal or a surgical opening in the mastoid behind the ear26. Bárány23 argued that the shape of the middle ear bones evolved to not only maximize hearing by AC, but also to minimize the hearing of one’s own voice and other internally generated sounds by the BC pathway. Von Békésy24 was of the same opinion as Barany, and further indicated that the ossicles might lie along an axis that minimizes their vibrations resulting from phonation. Von Békésy24 claimed that the vocal cords produce maximum vibrations along the vertical direction, but that their vibrations in the direction of the ear canal axes were smaller. This hypothesis was never experimentally verified. In a study on the middle ear ossicles vibrations during BC excitation in human temporal bone specimens, it was found that the effective vibration of the stapes was within 5 dB regardless of the vibration direction, thus disproving the hypothesis by Bárány and von Békésy27. Moreover, both experimental and modeling studies have indicated that the influence from the middle ear is some 10 dB below other contributors for BC hearing in the human29.There are indications that the vibration direction of the skull bone influences the BC perception25, calculations of the directional sensitivity of the cochlear vibration magnitudes showed small differences between the 3 orthogonal direction, where the difference between the maximum and minimum sensitivity was approximately 5 dB. In another study of a FEM of the inner ear, the response for vibration approximately in line with the axis of the oval and round window was greater than the responses from vibrations in other directions26. One limitation of that study was that only inertial effects was included while both inertial and compressional motion is important for BC sound perception18.Finite element models (FEM) of the human head and ear have been used to investigate the influence of the vibration direction for BC sound. In a whole human head FEM for auditory BC research30. The BC stimulation is applied to the guinea pig head in different directions, and the resulting three-dimensional velocity magnitudes at the cochlear promontory are obtained as well as the hearing threshold. By computing the cochlear velocity magnitudes in three dimensions at threshold for several stimulation directions, estimates of the directional sensitivity for BC vibration of the cochlea are obtained in the guinea pig.Consequently, neither experimental nor computational studies have resolved the issue of directional sensitivity for BC sound. The aim of the current study is to investigate the BC hearing sensitivity to the vibration magnitudes in three orthogonal directions of the cochlear bone and relate those directions to the anatomy of the inner ear. This is executed in guinea pigs where we recently developed a method for relating the BC hearing threshold to cochlear vibrations30. Here, the focus is on the threshold predictions based on the 3D vibration of the cochlear promontory. The stimulation directions were aligned with the x, y and z directions in overall coordinate system  is mainly in the z direction, the oval to round window direction (d2) is mainly in the x direction, and the base to apex of the cochlea (d3) is mainly in the reversed y direction.The hearing thresholds in guinea pigs with AC stimulation and a detailed analysis of the BC thresholds with the BC transducer mounted on the top stimulation position can be found in Zhao et al.tem Fig. A. CT scatem Fig. B. Three Figure One prerequisite for the analysis in the current study is that the relative vibration levels in the three directions at the cochlear promontory differ between stimulation directions. The more different the x, y, and z direction velocity magnitudes are at threshold for the five stimulation directions, the better the specificity of the cochlear bone vibration directions’ influence on BC hearing can be determined. The similarity of vibration levels at threshold for the 5 stimulation directions was here evaluated by computing the correlation between the velocity magnitudes at threshold for the response directions pairwise, i.e. the correlation is computed as the velocity magnitude at threshold between x and y directions, x and z directions, and y and z directions for stimulations in the five directions. These correlations are averaged over all guinea pigs and displayed for the three response direction combinations and 6 frequencies in Fig. n = 5) and number of animals (n = 22) according to the equationf is the stimulation frequency, index i stands for the ith animal, index k stands for the kth stimulation direction, v is the combinations of velocity magnitudes according to the estimation function (Eqs. 4.1 to 4.9), and a, b, and c, Eq. 4.6) that minimizes a cost function that is very similar to the variability measure in Eq.  direction gives the lowest variability of the eight, a difference of approximately 0.13. At 4 and 8 kHz, the z direction alone is the best predictor while the y and the d3 direction alone is the worst predictor. At the three highest frequencies, the variability is more similar for the eight combinations and there is no clear trend. One interesting finding in the variability analysis is that linear summation of the velocity magnitudes (Eq. 4.4) result in a slightly lower variability than the quadratic summation (Eq. 4.5) that has often been used as a predictor of hearing stimulation based on vibrations. Another observation is that at frequencies up to 8 kHz there are directions that produce lower variability than adding the velocity magnitudes in all three directions, either linearly or as the root of quadratic summation, but at the higher frequencies, no direction seem to give a clear advantage.For the other eight combinations of the velocity magnitudes, the variability in Fig. Even if the variability analysis in Fig. The other eight combinations of the three velocity magnitudes result in 5 to 8 dB average threshold estimation errors. The worst prediction was obtained by only using the y direction velocity magnitude at 2 kHz while at frequencies at and above 8 kHz, all estimations except the MSE method gave a mean absolute threshold error that fell within 0.5 dB of each other. Similar to the variance analysis in Fig. 2(35) = 285.44, p < 0.001] and frequency , and the degrees of freedom was adjusted according to Greenhouse–Geisser. According to the adjusted ANOVA, the method was significant , frequency was not significant while the interaction between method and frequency was significant . This indicates that there is a significant difference in the absolute threshold errors between the methods and that the absolute threshold errors at the tested frequencies differ between the methods. When the 95% confidence interval for the methods were analyzed, the MSE method was significantly better (lower threshold errors) than all other methods, the y direction results were significantly worse than all but the x and z direction results, and the d3 direction results were significantly worse than the linear summation and d1 direction results . All other 95% confidence intervals overlapped.The differences in average absolute threshold error in Fig. a, b, and c, as weights for the three orthogonal velocities that resulted in the best fit for estimating the vibration at hearing threshold, can be used as an estimation of the relative importance of the motion in the three directions. The computation of the hearing threshold based on the three velocities for the MSE method is according to Eq. 4.6 where Cx), and Cy and Cz), respectively. The relative contributions from the three directions was here analysed by comparison of Cx, Cy, and Cz. To facilitate comparison between animals, the contributors were normalized for each animal according toi is either x, y or z.The MSE algorithm estimates one weight for each direction and frequency. The estimation of the three coefficients, Sz) dominates at frequencies between 2 and 8 kHz with values between 0.55 and 0.68 where the maximum relative contribution from the other two direction falls between 0.4 and 0.5. This suggests that at these frequencies, the vibration in the z direction influence the hearing perception more than vibrations in the other two directions. This can also be seen in the variance and absolute threshold error estimates in Figs. d1) is most sensitive at frequencies between 2 and 8 kHz, while the direction in-line of the base to apex (d3) of the cochlea is most important at the highest frequencies. The least important direction of the three vectors presented in Fig. d2). The results in Fig. The results of this analysis are presented in Fig. 31.This study aimed to investigate the influence from different vibration directions on the perception of BC sound. This was accomplished by providing stimulation in 5 different directions at the vertex of a guinea pig head using a cubic brass connector. The rationale for using different stimulation directions at the guinea pig vertex was to achieve different combinations of the orthogonal vibrations at the cochlea that could be used to estimate their influence producing a sound perception by BC. To achieve this goal, the combinations of orthogonal vibrations at the cochlea should be as different as possible for the 5 stimulation attachments. Optimally, the vibrations at the cochlea should be one-dimensional with vibrations solely in the x, y and z directions sequentially with the change of the stimulation direction. However, the vibration of the cochlear promontory here cf. Fig.  indicateNot only were there vibration in all 3 spatial dimensions of the cochlear promontory with stimulation in different directions at the vertex, the resulting 3D velocities at threshold were correlated for the different stimulation directions Fig. , 5 is atAmong the nine different methods used to predict the hearing thresholds Table , the MSE22 suggested a method to compute the magnitude and phase for the skull vibration in the direction with the greatest motion. That type of computation could have been incorporated in the current study to characterize the three-dimensional spatial motion of the bone around the inner ear. However, the direction of the greatest vibration magnitude at the cochlea would be different between animals as well as between tested frequencies, and it would be difficult to draw conclusions relating to the directional sensitivity of the inner ear for BC excitation, which is the purpose of the current study. Since no direction dominated the magnitudes of the velocities in the three orthogonal directions , that is mainly in the z direction, gives the greatest contribution at frequencies up to 8 kHz while the direction from the base to the apex of the cochlea (d3), that is mainly in the y direction, is more important at the highest frequencies. Since the d1 direction is in-line with the in-and-out motion of the stapes, and also in line with the middle ear ossicles vibration direction (TM to stapes), this can be an indication that the inertial effects of the middle ear ossicles32 influences the BC hearing in guinea pigs at these frequencies. This conclusion has support in the findings in our previous study on BC hearing in guinea pigs where gluing the stapes footplate to the surrounding bone depressed the BC sensitivity significantly at 2 and 4 kHz, but not so much at the higher frequencies30. In the human, studies have identified ossicular inertia to be less important than other contributors to BC hearing29.When these findings are interpreted in the anatomy of the inner ear Fig. , the nord3 direction can be explained by a compressional mode of the cochlear shell. In the guinea pig, the cochlea protrudes into the middle ear space with only a thin bony shell surrounding it. With vibration in the direction of the cochlear base to apex, due to the minute thickness of the surrounding bone, this whole structure can be compressed forcing a fluid flow towards the oval and round windows and thereby creating a sound pressure difference between the scala vestibuli and scala tympani that generates a hearing sensation. It should be noted that this type of excitation is different from the compressional mode believed to be present in the human where the cochlea is surrounded by thick and dense skull bone18.The high-frequency influence from the One interesting finding was that the velocity in one direction predicted the thresholds better or equally well than adding all three velocities linearly or quadratically Figs. , 5. This27 showed that the relative stapes vibration, i.e. the in and out motion of the stapes in relation to the surrounding bone, was within 5 dB independently of the stimulation direction. The difference between the velocity magnitude of the bone in line with the stimulation and orthogonal to the stimulation direction was reported as 15 to 20 dB, meaning that the motion of the ossicles could not be explained by the out of plane motion of the bone itself. Consequently, even if the vibration of the bone around the middle ear in humans is orthogonal to the in and out motion of the stapes, relative motions appear in the in and out motion direction of the stapes. This motion is only slightly lower than motions obtained when the stimulation of the bone coincides with the in and out motion of the stapes. The result from the Stenfelt et al.27 study implies that motions in one direction of the bone can be transformed to another direction of the movable parts in the auditory system.To our knowledge, this is the first study that experimentally investigates the inner ears’ sensitivity to vibrations in different directions with BC sound. In a study on human middle ear ossicles motion in temporal bone specimens, Stenfelt et al.26 investigated the importance of the vibration direction of the inner ear during BC stimulation in a finite element model of the human inner ear. They reported that a vibration in line with the hook region of the cochlea resulted in greater basilar membrane velocities than stimulation in other directions. The direction of the hook region coincides with the direction between the oval and round windows in the human inner ear, and this direction was assumed most important in the modelling studies of Stenfelt33 as well. The result in the current study did not indicate that the direction between the oval and round window (d2) was more important than other directions. When investigating the variability measure and mean absolute error measure in Figs. d2 direction gave results that were overall slightly worse than the results in the d1 direction, but overall better than the d3 direction. Consequently, the direction that is most sensitive for BC stimulation can differ between the guinea pig and the human.Kim et al.26 was that only the inertial response of the cochlea was investigated, and that the model lacked the cochlear and vestibular aqueducts that has been found important for BC sound generation in the inner ear33. Even so, that study identified that there are directions of the BC vibration at the inner ear that is more efficient than others for hearing sound. That was also found in this study, especially at the lower frequencies there were directions that gave greater excitation of the inner ear compared to other directions. The current study did not try to identify the mechanisms for the difference in sensitivity with stimulation direction. It has here been speculated that a vibration direction in line with the direction between the oval and round windows would provide a greater inertial response in the cochlea, or that the compression component can be more excited when the stimulation is in line with the base to apex of the cochlea, other contributors to the inner ear sound pressure, such as sound radiated into the ear canal34, can be more efficient with other stimulation directions.One shortcoming in the study of Kim et al.Similar to findings in vibration experiments in humans, a stimulation in a specific direction on the surface of the guinea pig head result in response vibrations at the guinea pig cochlea in all three space dimensions. The best estimate of the hearing stimulation is obtained with a weighted sum of the vibration amplitudes in the three dimensions. However, only using one-dimensional response can be equally good as using a linear or quadratic summation of the three-dimensional velocities, but it can also result in much worse estimates. The results indicate that there are vibration directions at the cochlea, here in-line with the vibration direction of the stapes at lower frequencies and in-line with the base to apex of the cochlea at higher frequencies, which have an overall greater influence on the guinea pig BC response than other directions.This study was approved by the regional ethics board in Linköping and all experiments followed EU Directive 2010/63/EU for animal experiments.30.The experiments were conducted in 22 male guinea pigs (Dunkin–Hartley). The guinea pigs had a mean weight of 478 g and were between 6 and 10 weeks old at the time of the experiment. These animals were also included in a previous study, and a more detailed information of the preparation is provided thereThe guinea pig was anaesthetized with an intraperitoneal injection of Xylazine (10 mg/kg) and Ketamine (40 mg/kg). Additional injections of Xylazine and Ketamine was given at approximately intervals of 40 min to maintain deep anaesthesia. Oculentum simplex APL was provided to prevent the guinea pigs’ eyes from drying while bupivacaine (0.2 mg/kg) was administered to the guinea pigs’ ear canal. The Preyer's reflex was present in the guinea pigs and after the injections the fur on the vertex and around the ear was removed. A heating pad with a temperature of 37 °C was used to keep the guinea pig warm.The surgery involved an opening into the bulla which required an incision from the vertex down to the back of the ear. The soft tissue was removed and the bulla was opened to expose the middle ear structures and the round window (RW). The activity of the inner ear was obtained by electrophysiology measurements and one silver electrode was placed on the RW while two needle electrodes were placed in the homolateral back leg and the ipsilateral cheek.A computer connected I/O board with 1 output channel and 4 input channels  was used for signal generation and recording. An amplifier  amplified the RW electrode signal 10,000 times which was then sampled at a frequency of 102.4 kHz by the I/O board. The output channel of the I/O board provided the signal to a BC transducer, which was a motor unit from a BAHA Classic bone conduction hearing aid (Cochlear Inc.) that was attached to the guinea pig vertex. This transducer has a size of 15 × 15 × 8 mm and a weight of 7 g. The vibrations of the guinea pig’s inner ear that was generated by the BC transducer was measured by a three-dimensional Laser Doppler Vibrometer (LDV), which consisted of a Polytech CLV-3D sensor head and CLV-3000 controller. The three laser beams from the LDV was focused on the same spot on the guinea pig’s cochlear promontory, between the oval window (OW) and RW.To minimize the electrical noise during the electrophysiological measurements, the guinea pig was positioned inside an electrically and acoustically shielded chamber. A specially written software in LabView was used to generate the stimulus and record the electrophysiology signals. A brass cuboid adaptor was glued to the guinea pig bony vertex with dental cement (3 M ESPE Durelon carboxylate cement) Fig. A. This 6BC_guinea_pig). After finalizing the stimulation and recording at 2 kHz, the test continued sequentially at the test-frequencies . The estimation of 40 dB HLBC_guinea_pig was based on the results of BC thresholds in guinea pigs in a previous study30. After the measurements at all frequencies were conducted at a stimulation level, the level was decreased by 10 dB and the measurements were repeated with the decreased level at all test frequencies starting at 2 kHz. The level reduction continued down to 60 dB below the initial level, meaning that 7 stimulation levels for each frequency were measured. Based on the signal from the RW electrode, the compound action potential (CAP) was obtained for each stimulation level and frequency by averaging the 400 responses for each frequency and level. The BC measurements were repeated for all five stimulation directions . Figure The hearing measurements were conducted with the guinea pig positioned inside the shielded chamber. The stimulation had a total length of 10 ms consisting of a 6 ms long tone burst with 1 ms sine windowed rise and fall and 2 ms silence. This gave 100 stimulations per second that were present with alternating polarity for 4 s, resulting in a total of 400 stimulation presentations for each level and frequency. The measurements started at 2 kHz with a BC level of around 40 dB above threshold  in the abdomen. The vibration measurement of the cochlear promontory was conducted immediately after the euthanasia by placing the guinea pig on a vibration isolation table and aiming the three laser beams on the same spot on the cochlear bone between the OW and RW. A 2 s long chirp signal with frequencies from 1 to 50 kHz was supplied to the BC transducer and the resulting vibration on the cochlear bone were measured by the LDV and recorded by the I/O card. The Matlab function polyfit. Figure All analysis was done using Matlab. The magnitude of the P1 wave in the CAP was identified manually by first averaging the 400 measured responses with alternating polarities. The averaging of alternating polarities reduces the contribution from cochlear microphonic potentials in the measurements. Figure The stimulation voltage that resulted in 0 V CAP was computed (here termed threshold voltage) for each frequency and stimulation direction. Then the relationship between the voltage to the BC transducer and the vibration velocity in the three orthogonal directions of the cochlear promontory was obtained using the 3D LDV Fig. . Based oa, b, and c were determined by a restricted minimum mean square error method, hereafter referred to as the MSE method  of the 3D velocity magnitude Table . The sixod Table . The lasBy comparing how well these different combinations predict the hearing thresholds with stimulation in different directions, and thereby different combinations of 3D cochlear velocity magnitudes, the relative importance of cochlear vibration in a certain direction can be analysed.


Pain management in veterinary patients is a crucial component of appropriate patient care. Local anaesthetic drugs used in local and regional blockade can completely block the transmission of nociceptive impulses, decreasing both intra‐operative nociception and postoperative pain, while decreasing the potential incidence of adverse effects that can be associated with systemic boluses of drugs. For efficacy and safety, this class of drugs is recommended as part of the analgesic protocol in the majority of surgical procedures and traumatic injuries. Numerous local and regional blocks are proven effective in dogs and cats, thus providing the clinician with ample opportunity to include these blocks in practice. This manuscript, Part 2 of a two‐part instalment, focuses on brief descriptions of select commonly used local/regional anaesthesia techniques for dogs and cats that cover a multitude of painful surgeries/injuries and that can be implemented in any practice. In Part 1 of this topic, detailed information on local anaesthetic drugs commonly used in small animal practice was reviewed . This manuscript, Part 2 of a two‐part instalment, focuses on brief descriptions of select commonly used local/regional anesthesia techniques for dogs and cats that cover a multitude of painful surgeries/injuries and that can be implemented in any practice. Note th1.1The drug dosages used by the authors are those listed in the ‘commonly used drugs’ section of Part 1 of this manuscript  and of 1‐in to 1 3/8‐in length Lantz . BLIS is▪Volume of infiltration Lantz  :Cats 0.2–0.25 ml per siteDogs 0.25, 0.5, or 1 ml per site for small, medium and large dogs, respectivelyBOX 2▪Equipment: Syringes of appropriate size to hold calculated volume of drug and 25‐ to 22‐gauge needles of 1 to 1.5 inches in length. Occasionally, longer needles (2–3 inch) or specialized needles  are required.▪Volumes of infiltration: If different from the total calculated volume of drug, volumes are listed with each block.Unless otherwise stated with a specific block, all of the local anaesthetic drugs discussed in Part 1 .1.2All blocks described in this manuscript have been used by the authors unless otherwise indicated. The techniques for some of the blocks are described in other sources, often with detailed diagrams , the entire infraorbital canal is approximately 4 mm long, ending at the level of the medial canthus. Advancing a needle in the canal is typically not recommended due to the close proximity of the globe.st and 2nd molars in dogs and the 3rd and 4th premolars in cats.Tissues/area desensitized:  ventral and medial to the junction of the zygomatic arch and palatine bones, in a rostral‐medial direction, as if aiming for the opposite nostril. Advance the needle just dorsal to the palatal bone in the direction of the pterygopalatine fossa.oInfiltrate the local anaesthetic at the fossa and also while withdrawing the needle in order to block the caudal superior alveolar nerve.Tissues/area desensitized  in the dog and palatal root of the maxillary 4th premolar in the cat Lantz .Tissues/area desensitized: Desensitizes the oral side of the hard palate tissues. Used for analgesia for palate surgery.Mental nerve block Box BOX 8▪Technique:Palpate the middle mental foramen ventral to the mesial  aspect of the 2nd premolar.oIn cats, the middle mental foramen is at, or immediately caudal to, the apex of the mandibular canine tooth Lantz .Insert the needle into the soft tissue slightly rostral to that location.In medium to large sized dogs, local anaesthetic drug can be injected directly into the mandibular canal Lantz  and may In smaller patients, inject local anaesthetic directly under the gingiva immediately rostral to the foramen.nd, 3rd and 4th premolars were consistently desensitized  side of the mandible approximately halfway between the 3rd molar and the mandibular angular process in a dog  side. Palpate the mandibular foramen intraorally with one hand. With the other hand, insert the needle through the skin close to the medial aspect of the mandible and advance it dorsally in the gingiva to the area of the foramen. Aspirate and inject the anaesthetic  injury prevalence in humans based on articaine use may be due to a toxicity issue  is used by the author and was deemed the most effective and easiest of 5 different approaches to the retrobulbar block  half‐way between the lateral canthus and the middle of the lower eyelid. The needle can be inserted either through the skin or with the lower lid pulled ventrally and the needle inserted through the conjunctiva.Slowly advance the needle along the floor of the orbit (sometimes a ‘scraping’ sensation is felt as the needle scrapes the bone) and then dorsally and slightly medially as the needle reaches the back of the globe. Penetration of the orbital fascia can cause a slight ‘pop’.Aspirate and inject slowly. If significant resistance occurs, stop the injection and withdraw the needle slightly and try the injection again. Repeat withdraw/inject until the drug flows easily.BLIS can be used for tissue infiltration postenucleation but has not been described for the retrobulbar technique.Potential injection site complications include penetration of the globe  into the tissue at a point directly ventral to the atlas wing and caudal to the tympanic bulla. The vertical ear canal is palpable slightly rostral to this site and can be used as a landmark.Technique: Block the ▪auriculotemporal nerve by inserting a needle subcutaneously and slightly deeper  into the tissue directly above the most caudal aspect of the zygomatic arch, slightly rostral to the vertical ear canal, which is palpable at this site.Technique: Block the ▪Inject approximately 0.5–1.5 ml, depending on dog/cat size, at each location.▪Long‐duration blockade is ideal because aural pain can be profound and prolonged.▪A potential injection site complication is inability to close the eyelid due to temporary paralysis of the motor portions of the facial and/or temporo‐palpebral nerves  Figure BOX 12▪Technique: Insert the needle into the skin and muscle layers caudal to the proximal portion  of the ribs in 2–3 rib spaces cranial to and 2–3 rib spaces caudal to the area to be desensitized.Inject between 0.5–2.0 ml per site, depending on dog/cat size.Potential injection site complications include perforation of a vessel and pneumothorax. As with other blocks, intravascular injection is a potential complication and aspiration for blood is required to ensure that the needle is not in the costal artery or vein. Pneumothorax has been reported in human medicine. To decrease the likelihood of causing pneumothorax, the authors recommend using a small gauge needle (22‐G) and ‘walking’ the needle off the caudal edge of the rib, meaning the needle is repositioned using slight changes in the angle of entry (either ‘steeper’ or ‘flatter’) until it slides off the back of the rib. Aspirate for air to ensure that the needle is not in the thorax.If no blood or air is aspirated, inject at this point and continue to inject as the needle is withdrawn out of the muscle layers and skin. If blood or air is aspirated, withdraw the needle slightly and aspirate again. Inject when no blood or air is aspirated.▪Liposome‐encapsulated bupivacaine has been used for this block in human medicine  Box BOX 13▪TechniquesThree‐point blockoLocate the carpus and accessory carpal pad.oInject 0.1–0.3 ml (depending on dog/cat size) subcutaneously at three sites.1Medial to the accessory carpal pad, blocking the median nerve and palmar branch of the ulnar nerve.2Lateral and proximal to the accessory carpal pad, blocking the dorsal branch of the ulnar nerve.3On the dorsal‐medial portion of the carpus, blocking the superficial branches of the radial nerve.Enomoto four‐point technique for the manusoLocal anaesthetic is injected in four sites to desensitize the superficial branches of the radial nerve, dorsal branch of the ulnar nerve, median nerve and superficial branch of the palmar branch of the ulnar nerve and the deep branch of the palmar branch of the ulnar nerve.oThe description of the block is beyond the scope of this paper but the description and corresponding detailed illustrations can be accessed in Enomoto, Lascelles, & Gerard, oLiposome‐encapsulated bupivacaine has been used perineurally for similar blocks in human medicine  Figure BOX 14▪Percutaneous blind injection technique: Locate the acromion, the first rib and the jugular vein.Insert a nerve locator needle or a 2–4‐inch regular needle  on the axial side of the acromion. Aim the needle directly caudally or slightly caudo‐ventrally . Keep the needle in a plane sagittal to the rib cage—the tip of the needle may hit the axial side of the scapula. This is normal. Just withdraw slightly and redirect. Stop when the tip of the needle is even with the first rib or the caudal margin of the scapula (these are approximately the same location).Aspirate, then inject 1/3 of the local anaesthetic. Withdraw the needle to the middle of the scapula, and then to a site just before the needle exits the skin, and repeat aspiration and 1/3 injection at both locations.A potential injection site complication is risk of perforating the brachial artery.Use of nerve location or ultrasound guidance may improve block consistency when using this technique  has been described  nerve block . The needle is inserted at the caudal aspect of, and perpendicular to, the humerus. The needle will go through the long head of the triceps  into each testicle. Increased tissue pressure is felt as a sudden volume expansion of the testicle.▪NOTE: Some clinicians use only lidocaine for this block since the testicles are highly vascularized, potentially increasing likelihood of systemic drug uptake. The author uses bupivacaine or ropivacaine, following careful aspiration, because of the longer duration of action. There is no evidence that one drug is better/safer than another so the clinician should use experience and comfort with the drugs to decide which drug to use for this block.The drug migrates up the spermatic cord  and 4–6 mg/kg (dogs) lidocaine OR 1–2 mg/kg (cats) and 2–4 mg/kg (dogs) bupivacaine or ropivacaine into a syringe. If necessary, dilute with sterile saline so that the entire volume is 0.4–0.6 ml/kg.▪These dosages are conservative. In dogs, 8.8 mg/kg lidocaine OR 4.4 mg/kg bupivacaine  plus 2 ml of the same drug as an intra‐incisional injection caused no adverse effects  in a ‘pumping’ motion while palpating the sacrococcygeal region. The first movable space at the caudal end of the sacrum is either the sacrococcygeal or first intercoccygeal space. Either is appropriate and there is no need to determine which site has been identified.Insert a 22‐ or 25‐gauge needle through the skin ON MIDLINE at a 60–90‐degree angle to the skin surface, although a flatter angle (30–45 degrees) may also be used for the initial approach.Proceed slowly until the needle enters the space. Generally the needle will hit the vertebral bone and can be ‘walked off’ the bone, meaning the needle is repositioned using slight changes in the angle of entry (either ‘steeper’ or ‘flatter’) until it enters the space. A ‘pop’ may be felt as the needle penetrates the interarcuate ligament/ligamentum flavum but the lack of a pop should not be interpreted as incorrect needle placement, especially if a regular hypodermic needle is used. These needles are sharper than epidural or spinal needles and may pass through the ligamentum without causing a pop.Inject 0.1 ml/kg, depending on dog/cat size. There should be minimal to no resistance to injection.Do not inject air. Speculatively, an air bubble may cause an incomplete block in such a small space  or backward .Clip and aseptically scrub this region. Wear gloves. A small drape or sterile glove wrapper used as a drape is recommended.Insert an epidural or spinal needle (e.g. a Touhy needle) into the caudal portion of the LS space with the needle angled at approximately 45° from vertical.Slowly advance the needle until the epidural space is entered.oThe 'hanging’ drop often works .oSeveral ‘pops’ may be felt and can be used to gauge the depth of needle insertion.oIf bone is encountered, withdraw the needle a few millimetres, redirect slightly (steeper or flatter angle) and reinsert . Repeat this process until the needle enters the intervertebral space.STOP advancing as soon as the space is entered and slowly inject the drug.oAspiration at this point is recommended by some, including the author, to ensure that the needle isn't in a vessel (blood would be aspirated) or through the dura . However, others are concerned that the negative pressure of aspiration could damage delicate dural tissues.oIf blood is aspirated, the needle can be withdrawn slightly and re‐aspirated until there is no blood present, followed by injection of the drug. Some experts recommend withdrawing the needle completely and re‐starting the injection. The authors use the former option. If CSF is aspirated, the recommendation is to inject only one‐half of the drug volume to avoid excessive cranial migration of the drug with subsequent central nervous system (CNS) depression. Although commonly used, this recommendation is not evidence‐based.A test dose of saline can be injected to ensure that the needle is in the epidural space.oThe drug should inject easily if the needle is in a space.oThe most definitive determination that the needle is in the lumbosacral space is to stop injecting and take your thumb off the plunger. The fluid should momentarily continue to flow if the tip of the needle is in the epidural space.If the drug does not inject easily, the likely reason is that the needle was pushed slightly deeper when the syringe was attached. Withdraw the needle 1‐2mm and try again.Once drug has been injected, remove the needle and proceed with surgery.If local anaesthetic drugs have been used, the patient can be positioned with the surgical side down for approximately 5 min so that the drug can ‘bathe’ the nerves of the recumbent limb. If only opioids are used, this manoeuvre will not enhance the analgesia since the site of action is at opioid receptors in the spinal cord, not at local nerves. The efficacy of positioning as just described is questionable.▪Opioids are most commonly used but local anaesthetic drugs can be used alone or in conjunction with opioids.0.1 mg/kg morphine (preservative‐free is gold standard but morphine with preservative can be used). Other opioids provide a shorter duration than morphine but most are acceptable .▪Morphine is fairly lipid insoluble, and thus stays in the space and provides up to 24 hr of analgesia with minimal systemic uptake. Time to onset of analgesia is 30–60 min. The opioids will cause sensory blockade but are unlikely to cause motor blockade.▪Local anaesthetics have an onset and duration of action similar to their onset and duration at any other site. Local anaesthetics enhance the analgesic effects of the blockade , epidural haematoma or abscess, or hyperalgesia (very rare). An excessive volume of local anaesthetic could migrate cranially to the point of blockade of the nerves controlling the diaphragm, with subsequent impairment of ventilation. The recommendation not to exceed 6‐mls total volume of local anaesthetics is made to prevent this complication. Urinary retention may occur but is of low incidence and bladders are easily expressed  Box BOX 21▪Ring block: Inject local anesthetic drugs subcutaneously across the entire dorsum and entire ventrum of the pedus at a location approximately in the middle  section of the manus. The two subcutaneous injections will make a 'ring' of local anesthetic blockade.▪Enomoto technique for the pedusTwo blocks are proposed from deposition of dye near specific nerves. The distal crus block includes the tibial nerve, common fibular  nerve and saphenous nerve. The distal pes block includes two branches of the common fibular  nerve , tibial nerve and saphenous nerve.The description of the block is beyond the scope of this paper but the description and corresponding detailed illustrations can be accessed in Enomoto et al., Tissues/areas desensitized: All soft tissue structures of the pedus. Used in dogs and cats for painful surgeries or wounds on the paws, such as pad lacerations, torn toenails and removal of foreign bodies. Sciatic/femoral block  Box BOX 22▪Although no comparative data are published, a nerve finder or ultrasound guidance is likely to improve block accuracy, especially of the femoral nerve oThe nerve lies in the ‘femoral triangle’ on the inside of the thigh, bordered dorsally by the rectus femoris muscle, cranially by the caudal portion of the sartorial muscle, and deep by the iliopsoas muscle.oLocate the femoral artery and keep a finger on the artery to avoid accidental penetration. Direct the needle dorso‐medially to the artery to a depth equal to that of the artery.oA potential complication is perforation of the femoral artery so, as with all blocks, aspirate. Inject approximately 0.2 ml/kg local anaesthetic.oThe safety study for FDA approval of BLIS in cats utilized a suprainguinal approach to the femoral nerve at an increased dosage (NOCITA® product insert website). Liposome‐encapsulated bupivacaine has been used for femoral nerve blocks in humans  of this class of drugs, local anaesthetics are recommended as part of the analgesic protocol in the majority of patients undergoing surgical procedures or suffering traumatic injuries. There are numerous local and regional blocks described for use in dogs and cats, thus providing the practitioner with numerous opportunities to block nociception and pain transmission and provide more profound pain relief than is provided with the use of systemically administered drugs alone.Although manuscript preparation was supported by Aratana Therapeutics, who manufactures liposome‐encapsulated bupivacaine (NOCITA®), the authors feel that the information in the manuscript is a balanced view of the use of all local anaesthetics with detailed information on liposome‐encapsulated bupivacaine since it is a new product. The authors have no other conflicts.The authors confirm that the ethical policies of the journal, as noted on the journal's author guidelines page, have been adhered to. No ethical approval was required as this is a review article with no original research data.


A novel portable device has been developed and built to dynamically, and automatically, correct presbyopia by means of a couple of opto-electronics lenses driven by pupil tracking. The system is completely portable providing with a high range of defocus correction up to 10 D. The glasses are controlled and powered by a smartphone. To achieve a truly real-time response, image processing algorithms have been implemented in OpenCL and ran on the GPU of the smartphone. To validate the system, different visual experiments were carried out in presbyopic subjects. Visual acuity was maintained nearly constant for a range of distances from 5 m to 20 cm. Heys et al.3 also found an increase in the stiffness of the nucleus of the human lens, suggesting that it could be a major factor in presbyopia development.Presbyopia is the reduction of the accommodation range of the human eye. Many authors have performed experiments to understand the reasons behind such reduction, which involves the lens and the ciliary muscle. Using ex-vivo eyes, Fisher4. The accommodation range decreases through life until people are in their late fifties5. Even if the reduction in the accommodative range starts developing at early ages and it slightly increases throughout the whole life, it is not commonly noticeable for daily tasks until reaching the forties, when people start extending their arms to be able to read texts or see images. At the age of fifty, presbyopia has advanced up to the point that non-myopic people are unable to read small texts if they are held at a closer distance.Presbyopia develops through a long time and varies across different people. Children can usually accommodate more than 10 D, meaning that they can focus objects being as near as 10 cmThere are many available solutions for correcting presbyopia, being the most common progressive spectacles, but also multifocal contact lenses or intra-ocular lenses. Those are good solutions in general, however, with some drawbacks and limitations. Some of the aforementioned treatments are invasive such as intra-ocular lenses, refractive surgery, or even contact lenses. Others do not provide enough comfort or flexibility to the subject, as it is the case of multifocal or progressive spectacles. And all of them present trade-offs: either distance or near vision is enhanced at the expense of reducing contrast. Furthermore, only a limited range of defocus positions are available. The ideal presbyopia correction would be the recovering of the accommodation capabilities present in the young crystalline lens.The approach introduced in this paper is non-invasive and also offers a dynamic continuous focus range solution as in the natural lens. By using tunable opto-electronics lenses, it is possible to provide a focusing range only limited by the digital-to-analog converter of the system, in addition to the maximum and minimum focal length physically achievable by the opto-electronics lenses. In our prototype, a real-time pupil tracking system running on a smartphone is used to dynamically control the optical power required in the opto-electronics lenses. Providing a smooth and comfortable visual experience to the subject requires relatively fast changes in the applied power, therefore, a heavily integrated and computationally efficient system is essential to properly drive this Dynamic Auto-Accommodation Glasses.2 optical benchtop using several mirrors, lenses and a large high-speed camera6. Furthermore, it was attached to a desktop PC with a high-performance GPU (Graphics Processing Unit). Contrarily, the prototype presented and evaluated in this paper is a wearable solution, i.e., a completely portable and autonomous system that can be comfortably carried by a subject, where all the image processing, computing and control is performed within a smartphone. Developing an integrated device is important to test the glasses in a realistic environment. To measure the effectiveness of the proposed Dynamic Auto-Accommodation Glasses, we have performed visual acuity tests in presbyopic subjects to measure their visual acuity improvement while wearing the glasses.An initial proof-of-concept prototype was set on a 2 m6, the interest for opto-electronic devices for correcting presbyopia has increased and two other works have been recently presented8. Jarosz et al. have described a new lens featuring a 20-mm aperture and a 3 D range9. They have created a spectacles frame and mounted their tunable lenses with a laser-based distance sensor to control the required power of the lenses. This design is simple but has some limitations, if the subject wearing the spectacles does not stare at front of her/him, the power applied by the system might be wrong. Contrarily, our proposal uses binocular pupil tracking to accurately determine the distance where the subject’s eyes are looking at avoiding such problem.Since we proposed our first proof-of-concept system. have developed another solution using commercial parts for pupil tracking and depth sensing for the tunable lenses10. However, as far as we know their system is not truly a mobile solution since their pupil tracking processing  is done on a high-end desktop PC. Another work analysing the vergence-accommodation conflict in near-eye displays have used similar components as those in this paper11.Padmanaban et al12 but also small and low power displays specifically designed for wearables.The final goal is to use this device like normal glasses; therefore, we need them to become wearables. Some wearables devices have been specifically designed for tracking diabetes, sleep quality and quantity, blood pressure, heart monitoring, etc. Wearables are currently a big market and a lot of chips have been developed to build them, e.g., specific cores such as those from ARMThe proposed Dynamic Auto-Accommodation Glasses fit inside the wearable category, although due to their complexity, they have higher computing requirements than much simpler health-tracking and/or monitoring wearables. The higher computing needs directly affects the autonomy of the device. Therefore, an energy efficient solution is a requirement since running a highly compute-intensive algorithm such as pupil tracking in a mobile platform is challenging. We have deployed the image processing, pupil tracking and control system on a smartphone .13. Hasan et al. were able to create a tunable lens with a large aperture of 32 mm and a range of 5.6 D14.The performance of the system is critical for a fluent user experience since changes in accommodation occur relatively fast under natural conditions. The Samsung Exynos 8890 processor has achieved 24 frames per second while processing 320 × 240-pixel images which is enough speed to provide the required smooth experience to the user. Another key part of the system are the opto-electronic lenses. We have used a couple of tunable lenses which are able to change their focal length as a function of applied voltage . These are polymer-based lenses with a large range of optical powers (from − 10 D to + 10 D). There is a large research body around tunable lenses with different technologies being developed. Lin and Chen presented an electrically tunable focusing and polarizer free liquid crystal lens with a 6 mm apertureThe performance of the device has been measured and the visual acuity of 8 presbyopic subjects has been tested with and without the correction applied for different distances.A video of 250 frames under varying light conditions has been recorded using the cameras integrated in the Dynamic Auto-Accommodation Glasses at a resolution of 320 × 240 pixels. This video has been used to accurately measure the processing speed of the OpenCL implementation running on the smartphone GPU. According to the obtained results, the Samsung Galaxy S7 is capable of processing almost 24 frames per second taking 42 ms to process each frame. This is fast enough to provide a comfortable experience to the subjects. Therefore, it enables the system to generate a smooth response to the movements of the subject’ eyes.In order to measure the effectiveness of our wearable presbyopia correction glasses, a real-life experiment has been conducted with 8 presbyopic subjects with an average age of 62.5 (minimum 52 and maximum 78) years old. The subjects were informed about the nature of the experiment and all the possible consequences. Their informed consent was collected afterwards. The purpose of the experiment is to compare three different conditions. Far correction and near correction with trial lenses, and when the subjects were wearing the opto-electronic glasses. In the far correction condition, subjects were corrected for far using their refraction value with trial lenses. This correction provides clear far vision and blurry near one. The near correction case was set by adding a near addition lens of 2.5 D. The final case was the use of the Dynamic Auto-Accommodation Glasses. Visual acuity was measured at six different distances for each one of the three corrections. This experiment was performed with the subjects standing in front of the tests. Furthermore, the tests were always placed at the same location and the subjects moved back and forth to the different distances. Even when they were wearing the Dynamic Auto-Accommodation Glasses, due to their portability there was not any limitation to accomplish the task. The selected distances were: 5 m, 1 m, 0.5 m, 0.3 m, 0.25 m, 0.2 m. Figure With the far correction visual acuity decreases steadily as objects are closer. When the near correction was employed, subjects achieved their best visual acuity within a range of 2 to 3.3 D, with lower values for both closer and more distant targets. Visual acuity when using the Dynamic Auto-Accommodation Glasses was good for the whole range of tested distances.A paired t-test was conducted to compare the visual acuity of the far correction and the Dynamic Auto-Accommodation Glasses when looking at 0.5 m (2 D). There was a significant difference in the visual acuity measured without the glasses  and the visual acuity measured with the glasses  conditions t(7) =  − 4.3658, p = 0.003291.Furthermore, another two paired t-test were conducted to compare the visual acuity of the near correction and the Dynamic Auto-Accommodation Glasses at two distances: 5 m and 0.2 m (0.2 D and 5 D). For the first distance (5 m or 0.2 D) there was a significant difference in visual acuity measured without the glasses  and with the glasses  conditions t(7) =  − 9.4305, p = 0.0000314. For the second distance (0.2 m or 5 D) there was also a significant difference in visual acuity measured without the glasses  and with the glasses  conditions t(7) =  − 8.994, p = 0.00004284.A novel Dynamic Auto-Accommodation Glasses have been developed using a mobile GPU to power and control them. This wearable device is capable of tracking the pupil of a subject in real-time, calculate his/her gaze distance and apply the right optical correction. A novel OpenCL implementation of a pupil tracking algorithm has been implemented and optimized for smartphone’s GPUs. To validate the automatic presbyopia correction glasses, an experiment has been performed testing eight subjects and obtaining a sustained improvement in visual acuity in a wide range of distances.This device could have an impact in the life of millions of people around the world. Every person older than 50 years needs presbyopia glasses to read or look at their phones. Some presbyopic subjects only use presbyopia-correction glasses for near-distance work, however, their vision is blurred at medium or far distances and they need to remove the presbyopia glasses back and forth when changing the looking/working distances. These presbyopic subjects would be the ones that would benefit the most of a dynamic device such as the one presented in this paper. If our device would become widely available, it would change the behaviour of presbyopic subjects as they could freely look around like a (young) non-presbyopic person since everything would be automatically in focus.15. Though the speed of accommodation quickly decreases with age and the maximum they measured on adults was 18 D/s.The reaction speed of the device is critical to provide a smooth experience to the subject since the change in the optical power must happen very quickly yet smoothly. If the changes in the lens’ power were slow the subject would become stressed due to the reaction latency. On the other hand, if the changes were too abrupt the experience would be uncomfortable as well. Therefore, a smooth and fast response of the device to changes in the optical power required by subjects is critical. Our device fulfils those two requirements, providing a quick response under 200 ms and a smooth change in the optical power of the lenses at controlled speed of 50 D/s. This is close to the maximum speed found in children (33 D/s)10 is the bigger power range of the tunable lenses used. A larger range allows to focus very close targets, going beyond the normal focus range of an adult.An advantage of our device over other previously proposedHowever, our device has some limitations as it is right now. The field of view is relatively small due to the limited size of the aperture in the used opto-electronic lenses. In particular, the field of view is 43.6° for each eye, however, due to the portable nature of the device, the subjects can move their head and look at different positions. The binocular field of view ranges from 53.1° at 0.3 m to 43.9° at 10 m. The device is still a bit bulky to be comfortable for prolonged use, and the current battery capacity does not allow for an 8-h period of continuous utilization. Fortunately, most of these problems are addressable with an improved design, although some still pose some technological challenges, i.e., the limited aperture of the lenses. However, it is reasonable to expect that larger opto-electronic lenses will be developed in the upcoming years.From the user’s perspective the device provides a good visual experience that may require some adaptation. In the case of large changes in optical power, there are some visual effect due to the change in magnification. In addition, when the control eventually fails, some unwanted abrupt changes in the applied optical power can induce oscillations. A proper control procedure has minimized all these unwanted effects.The proposed Dynamic Auto-Accommodation Glasses comprise a set of parts which have to be integrated within a small and light frame in order to be portable and comfortable. This poses a number of design challenges which increases the difficulty of the setup, especially regarding the integration of the cameras, which have to be placed very close to the eye. To fulfil the wearable requirements, the smallest possible parts have been used whenever possible and a customized 3D frame has been created to properly integrate all of them. A customized board to hold the infrared LEDs has been created, and an opened micro-USB hub, with the wires directly soldered to gain space, has been employed as well. The two tunable lenses used are based on a shape-changing polymer. The lens is filled with an optical fluid, and the membrane consists of an elastic polymer. An actuator changes the pressure on the optical fluid dynamically, changing the shape of the membrane depending on the applied pressure. Therefore, by applying different amounts of current to the actuator the focal length of the tunable lens can be controlled.Figure 2 opto-electronic tunable lenses  and 2 lenses drivers.2 USB infrared cameras from Misumi .1 micro-USB hub with 4 USB ports.4 infrared LEDs.1 battery (300mAh 3.7 V) to provide power to the infrared LEDs.Samsung Galaxy S7 smartphone, utilized as the computing device and controller.The full list of parts mounted in the dynamic presbyopia glasses is the following:UVCCamera16. The tunable lenses are controlled through the COM port. In order to connect and communicate with the COM port in Android, the UsbSerial library was used.The cameras are compatible with the UVC standard (USB Video Class) which is not natively compatible with Android, so a library has been used to drive them: The overall process works as follows. The cameras send the recorded images directly to the smartphone where they are processed. After the subject pupils have been detected  the subject’s gaze is calculated (as described later). The lens optical power to be used, depending on how far the subject is looking at, is driven by the smartphone to the opto-electronic lenses. All the required parameters are set on a user-friendly Android application that we have developed for this purpose and there are no additional connections with any other device.There is a one-time initial calibration procedure where the subject is asked to look at a far point and the position of his/her pupils is recorded. This calibration step is almost instant (< 0.2 s) since only a few frames are needed for the calculation. As soon as the calibration is complete, the system is activated, and the opto-electronic lenses start to apply the calculated optical power. The smartphone is continuously grabbing frames from the cameras, therefore, if the previous frame is still being processed the current frame is discarded. After each image is processed the gaze of the subject is recalculated and the new optical power is applied by the opto-electronic lenses.f, yf) represents the position of the pupil while looking at far during the calibration step;  represents the position of the pupil recorded by the camera while looking at a near target;  is the center of the eye;  represents the actual position of the pupil while looking at a particular stimulus; α is the current rotation of the eye. Finally, the real position of the pupil is calculated using the formula:interpupil), which is calculated during the initial calibration, is also needed for calculating d as depicted in Fig. To calculate the current gaze of the subject some information from the calibration is needed and basic trigonometry is applied. First, the position of the pupil over the eye (ocular globe) is calculated. To do so the intersection between the eye and the position recorded by the camera is calculated. Figure The final equations for calculating the distance to the target follow. First, A and B are calculated as:It is important to note that in this process of calculating the distance to the target, the task with the highest computing demands is the tracking of both pupils from the stream of images grabbed by the two cameras.P1 the applied optical power is 1 D while for plane P2 it is needed to apply 5 D) such a big optical change will result in a discomforting experience for the subject. The reason is that human eyes do not react so abruptly. First, there is a reaction time; and second, there is a smooth transition from one optical power to the other. The average reaction time since a near target is shown and the accommodation starts is around 0.37 s17. Furthermore, the accommodation process has an average duration of 0.25 s for a 2-D accommodation range.In real situations, it is common for a subject to quickly look at different objects in different viewing planes. Such quick changes of both pupil locations are calculated by the system to apply the corresponding optical power to the lenses. However, if the two viewing planes are distant enough  the glasses react by applying the power needed by the subject. Similarly, when the two pupils are farther away from each other  the applied power is reduced accordingly.To illustrate the response time and behaviour of the presbyopia glasses, an example where a subject was asked to alternatively look at a far and at a near target is presented in Fig. 18 has been used for pupil tracking. This algorithm has been parallelized for desktop GPUs using CUDA in19 and later refined for binocular tracking and finer adjustment to elliptical pupils20. Here, we have followed a similar approach as in20 but instead of using CUDA, a novel implementation using OpenCL has been developed due to the incompatibility of CUDA with the used mobile computing platform. The Starburst algorithm can be divided into three main stages: a pre-processing phase to identify the corneal reflections introduced by the LEDs; a Top-hat transform is applied to the image that is thresholded. This image is dilated and the result corresponds to the detected corneal reflections. The border points of the pupil are searched as follows: a starting point is selected, which is usually the center of the image when no information about the previous pupil position is available. Then, a variable number of “rays” going from the selected center towards the limits of the image are processed. If a change in intensity bigger than a threshold is found along the ray, the point is considered a potential border of the pupil. The center of mass of the potential border points is calculated. If the distance between the current center of mass and the previous center is smaller than a threshold, the algorithm has converged, and we can proceed to the next stage. Otherwise, the search is repeated and using the current center of mass as the new pupil’s center.The Starburst algorithmsteady center, a RANSAC (Random Sample Consensus) ellipse fitting is applied to the complete set of border points and the best fitting ellipse is selected as the final pupil. From the previous high-level description, it can be noticed that the Starburst algorithm is highly compute demanding, since requires to process a very big amount of data.Finally, when the search of the border points of the pupil has converged to a novel implementation of the pupil tracking algorithm has been developed from scratch by using OpenCL to take advantage of the heterogeneous architecture of mobile SoCs. The OpenCL implementation runs on the smartphone’s GPU for all the image processing and pupil tracking but the smartphone’s CPU still does a significant work managing the cameras, the opto-electronic lenses and the GUI of the Android application. The smartphone used is the Samsung Galaxy S7 running Android 7.0 which integrates a Samsung Exynos 8890 SoC, a screenshot of the controlling app is shown in Fig. The mobile GPU implementation has been used for running the tests with the real subjects since it is the computing platform fully integrated in our presbyopia glasses prototype Fig. , and so Vectorized memory accesses allow the GPU to pack into one load operation several pixels, therefore, increasing the efficiency of the operation and the effective bandwidth. As a result, the performance is increased due to the reduced waiting time for more pixels. Vectorized memory accesses are especially important for image processing tasks  which are run at the beginning of the pupil tracking algorithm. Vector data types are also used to store the location of the points found in the border of the pupil.Local memory is capable of achieving much higher bandwidth than the device memory used to allocate the OpenCL buffers, although local memory is a much scarcer resource. Again, using local memory is useful for image processing tasks where some memory positions are accessed several times by the same threads or different ones within the same work group (warp). We have also used local memory for applying the RANSAC and for communication in the search points step. In the latter case, the local memory is dynamically reserved.native_sin, native_cos and native_sqrt. The half data type is used for searching the spots and for the RANSAC step. Half data type has two advantages over float and double types: they are faster to compute due to the reduced precision and also use less bandwidth so the amount of values loaded (or stored) is potentially up to 2× or 4× more than when using floats or doubles, respectively. However, due to the reduced precision the results are less accurate. It is worth noting that the half data type has had a good support on mobile GPUs for some time, while desktop GPUs have been slower supporting this reduced-precision data type.Native operations are used to calculate angles in the search of the pupil’s border points. Native math functions are optimized implementations which obtain better performance by means of reducing the precision of the operation. Some of the native operations used are: separable filters have been also used to optimize the image processing functions leading to a further reduction of the execution time.Kernel fusion can reduce the execution time in some cases. For instance, kernels with low execution times waste a lot of time due to the overhead of the OpenCL API calls; and also kernels which store data onto the global memory which is then loaded by the next kernel with no inter-group synchronization required. In particular, we have joined the kernels which perform the last part of the Top-hat transform and the thresholding operation, avoiding one kernel launch and saving memory operations. Finally, Every subject was informed about the requirements and aims of the study, and a written informed consent obtained, following the tenets of the Declaration of Helsinki. The ethics authorisation to perform the measurements was granted by the University of Murcia Research Ethics Committee.


The dementia epidemic continues to affect families across Canada. The number of persons living with dementia (PLWD) is projected to reach 1.1 million over the next 20 years, placing further financial and resource constraints on the Canadian healthcare system. Caregiver education is vital in ensuring the quality of life and safety for PLWD and can increase the time they are able to live at home, which is correlated with positive outcomes for both PLWD and their caregivers, and a reduction in system costs. However, current educational support often requires individuals to travel to local, urban service care centers and educational content is often provided in English, which can exacerbate the difficulties faced by marginalized caregivers  who are caring for PLWD. To address this issue, a team of researchers developed a serious game called “SafeHome” that teaches safety strategies by having players identify and rectify potential hazards in the home setting that may negatively impact on PLWD outcomes, such as falls. A usability study was conducted using an adapted, validated questionnaire and semi-structured focus groups to better understand users’ experience and obtain suggestions for the SafeHome serious game improvement. Results indicated that 80% of the participants were satisfied with the activities provided through SafeHome. All participants (n = 13) made recommendations for improving the usability, functionality, and comprehensiveness of the educational content. This feedback will inform future iterations of SafeHome and add valuable contributions to the growing literature on innovative e-learning resources that support PLWD and their caregivers. The rising prevalence of dementia in Canada correlates with the disease’s emergence as a leading healthcare challenge worldwide ,2. In heThe preference of many Canadians to age at home is an opportunity to improve the quality-of-life outcomes for persons living with dementia (PLWD). A recent analysis shows that the rate of PLWD who are 65 years of age and over living at home will increase from 55% in 2008 to 62% by 2038 . While tModern improvements to caregiver education and healthcare accessibility have resulted in PLWD being diagnosed earlier, their condition being managed more safely, and have opened doors for caregivers to help PLWD age at home for longer . Since sIn Ontario, dementia education and caregiver support programs are typically provided by healthcare professionals and often require caregivers to travel in person to meet with them at service centers. This method of support can be inconvenient for marginalized and underserved caregivers . Arguably, this demographic who have difficulty traveling, taking time off work, and communicating in English, may stand to benefit the most from such services, highlighting the need for more flexible solutions . ResearcSerious games leverage the power of game-based learning to engage and support learners in developing new knowledge and skills through several gaming strategies. Game-based learning also enables learners to undertake specific tasks and experience situations that would otherwise not be feasible due to cost, time, distance, and logistical and safety reasons. Hence, the aim of our study was to offer educational content from the Beyond Words workshop in a digital format, a game titled “SafeHome”, to support home-dwelling PLWD and their caregivers with online resources and to evaluate the serious game’s usability with the caregivers. Beyond Words workshopThe Beyond Words workshop was developed at Baycrest Health Sciences by Dr. Regina Jokel. Baycrest is a global leader in geriatric living, healthcare, research innovation, and education with a special focus on brain health and aging. The workshop provides education, training, and support to caregivers of PLWD while covering important topics such as nutrition, behavioral change, normal/abnormal aging and warning signs for Alzheimer’s disease, and practical communication strategies alongside environmental modification to enable a good quality of life. These strategies are placed in the broader context of brain health and describe modifications to the physical setting that create a safer environment . The mulIn addition to caregiver education, the home environment can also positively influence communication in a social setting. It is often the case that PLWD do not engage in conversation when they are upset, agitated, or at substantial risk of a fall or injury. The physical environment for PLWD is an important aspect of care when providing support at home. Dementia is a chronic, progressive disorder characterized by a decline in cognitive ability, visual-spatial memory, reasoning, and memory, which can have a significant impact on mobility and navigation ,20. A coManipulating the aspects of the physical setting can therefore prevent unsafe behaviors and greatly diminish the likelihood of a fall or injury, while simultaneously helping to stabilize emotional states and improving social interactions. The opportunity to ask questions, network with other caregivers, and share experiences with dementia caregiving helps to reduce social isolation and develop healthy coping strategies. Hence, while the Beyond Words workshop can be highly beneficial like many caregiver programs, its accessibility is limited to those who live nearby, are able to take time off from work, and speak English fluently. Thus, as stated earlier, the aim was to design a serious game to specifically follow the Beyond Words workshop by providing workshop content within a serious game environment that can be accessible to interested parties without having to physically attend the workshop. Further, the game supports home-dwelling PLWD and their caregivers with online resources to evaluate the game’s usability.Intervention: SafeHome serious gameDesign The game was designed for caregivers of PLWD. Generally, a serious game is considered a broad umbrella concept encompassing gamification, with a special focus on the use of gaming for educational purposes. The serious game includes game elements and feedback  of the SafeHome game. Although the design went through multiple iterations based on the feedback provided by the study team, the purpose of the feasibility testing with end-users was to identify further areas of improvement to be made in following iterations of the design.The main application was coded using the Unity game engine , which is one of the most popular engines used to create three-dimensional (3D), two-dimensional (2D), virtual reality, and augmented reality games, as well as commonly occurring representations. SafeHome was originally developed for tablets and was translated to a web version by equating on-screen touch commands to mouse clicks. SketchUp , a freely available open-source software, was used to create the 3D models for the initial room design. The application uses an Extensible Markup Language (XML) sheet for all the text in the game so that the team can edit and change the text easily, as well as easing the task of adding more languages to the application in the future with XML style tags designating each language’s text. SafeHome uses a double-axis control system for navigating through the room. As this was a prototype, a double-axis system was chosen due to ease of implementation. A more refined version in the future would explore alternative interface approaches.To control the navigation, there are two on-screen controllers (white circles) for the player to use on the mobile version Figure . The lefFunctionalityThere are 12 hazards in total and the game is only complete when the user has identified all the hazards. When the user taps on an object, they will be prompted with a textbox asking if the object is in fact a safety hazard Figure . When an object is correctly identified, a pop-up text box appears with suggestions on how to mitigate the risks of the hazard  Figure . For exaItems the user has not found also appear in the taskbar with a shadow effect (black silhouette) to offer hints to the player as to how many remaining hazards need to be found before completing the game. There are also three objects that are not real hazards, which can be tapped; these objects are the door, the plates, and the fridge. The door is not a hazard because it is already locked; the plates and the fridge could potentially be hazards in certain scenarios, but do not cause major harm given the current narrative. After the activities are completed, the player is provided with a test-your-knowledge quiz. The quiz utilizes the same tasks as the second activity but removes the sidebar to increase difficulty. The quiz is enabled once a player has identified all the hazards. In this new scenario, the player is asked to identify all the hazards but is not provided with the shaded banner that hints as to which hazards are left to identify. In other words, players are expected to remember what they have learned and move quickly and identify hazards in the room without aid.The game is currently available in English. The second prototype will provide functionality that allows the user to choose from several prominent languages in Ontario, including French, Mandarin, Italian, and German. Avatar GuideTo make the game more user-friendly and approachable, a 2D-animated avatar dog named Nikki was added Figure .The application has a tutorial cutscene where Nikki explains to the player the purpose of the app and how to navigate the system. Nikki helps guide the player throughout the game by giving a puzzled look when the player taps on an object, a smile if a hazard is identified correctly, and textual feedback on the player’s choices, confirming or rejecting their selection. Users can feel as though they are communicating with Nikki throughout the experience, which makes it a more engaging and game-like environment that allows for mistakes and provides friendly, helpful feedback. The reason for choosing a dog as the helpful on-screen guide stems from the idea of service and rescue animals. People commonly identify the dog as an animal that provides help for people with disability or for those whose duty it is to keep others safe in search and rescue, and we hoped to create the same feeling when working through the game.ApproachThis was an exploratory, mixed-methods study that included administering surveys and conducting a focus group. The 3-hour study session protocol involved a 15-minute welcome segment, 30 minutes of training to use the SafeHome serious game, 45 minutes of playing and allowing participants to familiarize themselves with the app, 30 minutes for completing an individual survey, 55 minutes for participating in a focus group, and five minutes of debriefing. Each participant received a $50 gift card for their time.ParticipantsA convenience sample of 13 participants was recruited from a list of previous attendees of the Beyond Words workshop, hosted at Baycrest Health Sciences Centre, to test the feasibility and usability of the SafeHome app. Eight of those participants participated in the focus group in addition to completing a survey post-workshop. In order to meet inclusion criteria, participants had to be caregivers of a PLWD, be able to communicate in English, and speak a second language that was covered by the design of the SafeHome app .The sample size for the study was calculated bearing in mind the resource constraints such as study room availability but also accounted for ideal focus group size which affords a general saturation of ideas . Also, tData collection instrumentsThe survey instrument was based on the Questionnaire for User Interaction Satisfaction (QUIS) with the purpose to assess users’ subjective satisfaction with specific aspects of the human-computer interface . QUIS itThe purpose of the focus groups was to ask questions that were not covered by the QUIS, including recommended changes or additional educational elements, comprehension of the learning material, and whether independent problem-solving was facilitated. Research assistants were instructed to lead a discussion among the focus group with a number of open-ended questions and follow-up prompts: (1) What aspects of SafeHome did you find most useful, and why? (2) What aspects of SafeHome did you find least useful, and why? (3) Did you find navigating the game easy? Why/why not? (4) What can we do to improve the ease-of-use of the SafeHome app? (5) Did you find the game engaging? Why/why not? What can we do to make it more engaging? (6) Did you learn anything about room set-up that would make it safer for a person with dementia? (7) Would you recommend this game to other caregivers of people living with dementia?Comments and observations were transcribed verbatim, digitized, and later coded using inductive thematic analysis.SurveyThe overall user reactions to the SafeHome were positive with 71% of respondents indicating the experience with the tool was “wonderful” or “almost wonderful”. Approximately 86% of app usability participants found the application to be “stimulating” and 86% of the participants found the application to be appropriately flexible. Most respondents indicated feeling satisfied with the purpose of the app, and there appeared to be little correlation between the ease or difficulty of the user experience with the overall experience of app use as wonderful or frustrating. Focus groupQualitative feedback from the focus group was coded into five main themes: (1) design aesthetics, (2) functionality, (3) content, (4) miscellaneous suggestions, and (5) degree to which game was a helpful teaching aid. Although many suggestions and comments were raised by participants, we focus here on the items that were mentioned more than once by various participants. Feedback from focus groupDesignIn terms of aesthetics, participants recommended there be more contrasting colors to differentiate between items that can be tapped and the background setting.FunctionalityParticipants found the reset button useful to reorient the players’ perspective in-game but suggested that the button be larger and more obvious, so the function may be easier to access. A few participants pointed out that the controls were too sensitive and so many movements were too fast and difficult to navigate. Based on this feedback, our second prototype will consider making changes to the controls and navigation features. ContentParticipants suggested that more rooms should be added, so that caregivers may discover objects in other settings throughout the entire house. One participant suggested an added task, whereby the player identifies the correct place to safely store an item . One participant highlighted that locking the cupboard to prevent access to harmful items may “cause negative emotions”. MiscellaneousThere was a discussion around the appropriateness of the avatar guide (the dog). One participant suggested that it would be good to have more characters to choose from as a guide. Another suggested it be a robot avatar, “If you’re talking about our life today, robot will be nicer because robots are in fashion and they give you welcoming in airport and service in many places.” It is important to acknowledge that strategies should be implemented flexibly and account for individual differences.Educational ToolOne participant commented, “To me, it was useful to see it on a screen because there are so many things in that kitchen that you take for granted.” Some participants mentioned it was helpful even to watch others play the game and just be a spectator, as this would also remove the stress of being tested. The benefit highlighted here was that it was still a more entertaining method of learning (using a game), and that “you remember longer” compared to just being taught in the traditional lecture style. There was a general agreement among participants that they would recommend the game to other caregivers. Interestingly, another use-case emerged for such a game: to help prepare new parents by “baby-proofing” a house.http://forms.baycrest.org/safehome/. Although there is currently no plan to market this product , participants responded positively and provided recommendations to the design that could encourage future iterations.SafeHome is available online for free at Future iterations of the game would include increasing the color contrast within the app to better suit the needs of a diverse audience , by introducing flexibility in the sensitivity of buttons (addressing diverse dexterity) and changing the appearance of the avatar to be customizable to user preferences. In addition to expanding the app to include a greater number of rooms and potential hazards to increase the content and thereby comprehensiveness of the game, we will introduce scoring at the end of each session (so that users can track their improvement); and, if provided formally as part of a caregiver training course, a certificate of completion with user name will be awarded in PDF form at the end of the game. In terms of evaluation, similar usability testing followed by a focus group session would be conducted after each substantial iteration of the app. As a first step in scalability, we will approach Dr. Regina Jokel to discuss offering SafeHome game to participants in the upcoming Beyond Words workshops and using her network to reach out to healthcare providers with access to a similar demographic of caregivers.The SafeHome game demonstrated that it is feasible to convert content from an in-person caregiver education workshop to a digital format. It also illustrated that gamification along with visuals can provide a richer learning environment. The majority of our participants were able to navigate the application with minimal instruction and frustration and found SafeHome to be entertaining and helpful. As expected, participants provided a multitude of suggestions to improve the ease-of-use and functionality of the game. They also provided ideas about expanding the content of the app. By detailing the design elements and process, this paper adds to the important, although underrepresented, body of literature on virtual game design for caregivers of PLWD.


Clinical observation and inspection are fundamental to the practice of medicine. They are central aspects of the physical examination as they lead to accurate diagnoses and treatment. The terms observation and inspection are often used interchangeably, although inspection refers specifically to what we can observe visually on the surface of the body, while observation is a broader term that refers to the careful use of our senses to gain physical as well as behavioral information. Something that is immediately visible when evaluating a patient is the color of the skin. This can provide important clues to the underlying medical problem and guide the clinician towards a diagnosis. Suffice to mention the skin pallor in anemia, the yellowing of the skin in jaundice, the bluish hue seen in cyanosis, the cherry red skin color of carbon monoxide poisoning, the patchy loss of skin color in vitiligo, the mottled, marbled appearance of the skin in livido reticularis, the orange skin pigmentation of carotenemia, among many others.While working at one of our walk-in clinics, I saw a patient who presented with complaints of fatigue, weight loss and abdominal pain. The man, whom I will name Juan, was very concerned because his symptoms were impairing his ability to work and earn a living. He had previous history of histoplasmosis and was unclear if he had received proper treatment for it or not. I continued interviewing the patient while perusing his electronic medical record (EMR), my eyes darting back and forth from him to the computer screen and vice versa.   I saw multiple visits in several outpatient primary clinics, walk-in clinics,  and emergency departments, all with similar complaints. A number of tests and imaging studies were done, but the various clues to his disease didn't appear to have been tied together at any point in time. It occurred to me that his skin had an unusual tan.   I started looking at him more intently,   my eyes shifting up and down from his face to his hands.   The knuckles were very dark compared to the surrounding skin. I approached him, and on further physical examination, I noticed hyper-pigmented gingival patches, black longitudinal nail bands and darkened palmar creases.   The patient's wife became aware of my intense scrutiny of Juan's hands and face, and rightfully guessed that I must have been puzzled by the color of his skin."Doctor, my husband's skin was much lighter, just like mine," she said in Spanish, her native language, while pointing at her own face. She added that his color had changed during the past several months, becoming progressively darker.That was the clue, purely based on clinical observation, which allowed the diagnosis to be made even prior to further workup.In Juan's case, the hyperpigmentation of the skin unmistakably pointed towards the diagnosis of adrenal insufficiency,  especially once considered in association with the other less specific symptoms of fatigue,  weight loss and abdominal pain.  In addition to that,  several tests found in the  EMR showed electrolytes abnormalities and   MRI  findings of bilateral enlargement of the adrenal glands, which are seen in disseminated TB, fungal infections, lymphoma and other conditions, all resulting, if untreated,  in adrenal insufficiency.  The MRI was one of the many imaging studies requested for further workup of the abdominal pain, but nobody seemed to have paid attention to the enlarged adrenals at any of the various office visits performed by different health care professionals.I referred Juan to my endocrinology colleagues for an expedited evaluation.  Further tests were performed and he was officially diagnosed with primary adrenal insufficiency due to disseminated histoplasmosis.  Juan was treated accordingly and he's now thriving again.-Yet, how could Juan's diagnosis be missed for so long? Granted that the onset of adrenal insufficiency is often insidious and nonspecific, how is it possible that nobody paid attention to the striking skin discoloration and the mounting constellation of signs and symptoms? Also, despite the availability of various abnormal tests and lab reports in the EMR pointing towards the possibility of adrenal insufficiency, there was still a significant delay in diagnosis.  This delay in diagnosis can be explained by several factors which are the results of fundamental changes in the practice of medicine and medical education during the past decades:  lack of continuity of care, poor communication among health care providers compounded by the use of different EMR systems,  and a general decline in clinical skills.  The continuity of clinical information is in large part dependent on the continuity of the physician-patient relationship,Primary care physicians are also more and more pressed for time, with increasing patient panels and shorter office visits, making it more challenging for them to attentively listen to their patients, to carefully review the record, to gather all pertinent information, and share that information with other colleagues involved in the care of those patients.--There is a consensus that clinical skills have been greatly deteriorating during the past twenty years, with some reports dating back to the 1970s and 1980s.Juan's case also reveals how the decline in clinical skills and the progressive fragmentation of care can lead to a loss of the immense value associated with knowing, talking,  and listening to the patient, getting a good history, and performing an accurate physical exam. This close and considerate attention is how the physician and the patient establish a rapport of trust and respect, which transcends any other considerations. Such trust and mutual respect should be at the heart of the practice of medicine.The authors declare that they have no conflict of interest.


The North Atlantic warming hole (NAWH) is referred to as a reduced warming, or even cooling, of the North Atlantic during an anthropogenic‐driven global warming. A NAWH is predicted by climate models during the 21st century, and its pattern is already emerging in observations. Despite the known key role of the North Atlantic surface temperatures in setting the Northern Hemisphere climate, the mechanisms behind the NAWH are still not fully understood. Using state‐of‐the‐art climate models, we show that anthropogenic aerosol forcing opposes the formation of the NAWH  and delays its emergence by about 30 years. In agreement with previous studies, we also demonstrate that the relative warming of the North Atlantic under aerosol forcing is due to changes in ocean heat fluxes, rather than air‐sea fluxes. These results suggest that the predicted reduction in aerosol forcing during the 21st century may accelerate the formation of the NAWH. Using CMIP6 and CESM‐LE simulations, we show that aerosol forcing generates a global cooling trend with a warming in the North AtlanticThis trend opposes the North Atlantic warming hole trend due to greenhouse gasesAerosol forcing delays the formation of the North Atlantic warming hole by about 30 years The main aerosol effect is to reduce FSWSFC by direct interaction (scattering and absorbing) with the shortwave radiation in the atmosphere . The decrease in QSH and QLH over the North Atlantic (stronger surface cooling) due to aerosol forcing is caused by the local increase in surface temperatures.A temperature increase in the North Atlantic due to aerosol forcing Figures  and 2 coFigure The CMIP6 hist‐aer data are based on only eight different models (that were available as of June 2020). Using model ensembles partially removes the spread due to the different model formulations Figure ; howeverExamining the surface temperature difference between the full historical forcing and the fixAER . This might be a result of the way these ensembles were constructed, running a single simulation between 1850 and 1920 and initiating the large ensemble based on the conditions in this specific simulation at 1920 . Hence, it is to be expected that this single simulation does not have the same temperature fields as the preindustrial control run, with which the temperature anomalies are compared. In addition, we note that in the Full‐forcing case the ensemble mean temperature difference demonstrates a reduction between 1920 and 1960, followed by a recovery up to 1990. This trend is consistent with the strongest aerosol effect on the AMOC during the latter period  predicted under global warming (Chemke et al., We quantify the effect of aerosol on the NAWH compared to other anthropogenic forcing agents, in both CMIP6 models and the CESM‐LE by examining the local temperature contrast and show that it delays the formation of it by about 30 years. It should be noted that a recent study demonstrated that in CMIP6 models AMOC is more sensitive to aerosol forcing than in CMIP5 and in observations (Menary et al., In future decades the aerosol forcing is expected to decline. Our results suggest that the predicted reduction in aerosol forcing will accelerate the formation of the NAWH, which could have important implications for the climate in the Northern Hemisphere (O'Reilly et al., Supporting Information S1Click here for additional data file.