Hallmark social activities of humans, such as cooperation and cultural learning, involve eye-gaze signaling through joint attentional interaction and ostensive communication. The gaze-signaling and related cooperative-eye hypotheses posit that humans evolved unique external eye morphologies, including uniformly white sclera (the whites of the eye), to enhance the visibility of eye-gaze for conspecifics. However, experimental evidence is still lacking. This study tested the ability of human and chimpanzee participants to discriminate the eye-gaze directions of human and chimpanzee images in computerized tasks. We varied the level of brightness and size in the stimulus images to examine the robustness of the eye-gaze directional signal against simulated shading and distancing. We found that both humans and chimpanzees discriminated eye-gaze directions of humans better than those of chimpanzees, particularly in visually challenging conditions. Also, participants of both species discriminated the eye-gaze directions of chimpanzees better when the contrast polarity of the chimpanzee eye was reversed compared to when it was normal; namely, when the chimpanzee eye has human-like white sclera and a darker iris. Uniform whiteness in the sclera thus facilitates the visibility of eye-gaze direction even across species. Our findings thus support but also critically update the central premises of the gaze-signaling hypothesis. From an early age, we are able to detect the direction others are looking in (known as eye-gaze) and make eye contact with each other to communicate. The front of the human eye has a large white area known as the sclera that surrounds the darker colored iris and pupil in the center.Compared to us, chimpanzees and other nonhuman great apes have sclerae that are much darker in color or at least not as uniformly white as human eyes. Some researchers believe that the white sclera of the human eye may have evolved to make it easier for other individuals to detect the direction of our gaze. However, there is a lack of experimental evidence as to whether white sclerae actually helps humans to distinguish the direction of eye-gaze.Here, Kano, Kawaguchi and Yeow presented human and chimpanzee participants with images of other humans and chimpanzees on a computer screen and asked them to indicate the direction of eye-gaze in each image. The experiments found that both humans and chimpanzees were better able to discriminate the directions of eye-gaze from the images of humans than those of chimpanzees, particularly when the images were smaller or more shaded. Moreover, artificially altering the eyes in the chimpanzee images so that they were more human-like – that is, had a light-colored sclera and a darker iris – enabled both humans and chimpanzees to better discriminate the eye-gaze directions of the chimpanzees.Kano, Kawaguchi and Yeow’s findings indicate that white sclerae do indeed help both humans and chimpanzees to discriminate the direction of eye-gaze, even though only humans have white sclerae. This is likely because humans use eye-gaze in key social activities , indicating that white sclerae may have evolved to enhance human-specific communication. To learn more about this type of communication, future research could focus on finding out when white sclerae first evolved. In humans, eye-gaze is employed in critical ways for conspecific communication during social activities such as cooperation, teaching, and language learning . Humans Relatedly, one influential hypothesis, the gaze-signaling hypothesis , proposeuniform whiteness in humans’ exposed sclera; i.e., depigmentation all the way from the iris edge to the eye corners  was reversed by inverting the lightness  values of the eyeball images in the faces . This maWe developed five sets of hypotheses and predictions . H1 is o2 = 37.08, df = 1, p<10–8). We also found that their performance was worse in trials presenting smaller and more shaded stimuli  in two experiments. Experiment 1 presented participants with the stimuli of both humans and chimpanzees with normal contrast polarity at four stimulus levels (L1–4) varying in size and brightness. We tested the effect of stimulus level and species on participants’ correct responses  in a binomial generalized linear mixed model . Each chimpanzee completed a minimum of 20 test sessions. To avoid the ceiling effect, we incremented the stimulus level also during the test phase when chimpanzees showed high performance in target trials based on the same criteria. We tested the effect of stimulus species in binomial GLMM on each chimpanzee’s correct responses  during the test phase and found that all three chimpanzees performed significantly better for the human stimuli than the chimpanzee stimuli  passed all the required training and subsequently participated in test phases (see α = 0.05/2). We compared each chimpanzee’s correct responses in target trials across Test A1 and Test B in GLMM and found a significant interaction effect between stimulus species and phase in both chimpanzees . To examine these observed interaction effects further, we performed simple effects tests (Experiment 2 tested two (Natsuki and Hatsuka) out of the three chimpanzees. Pendesa was dropped from this experiment because she took about twice as many training sessions as the other two chimpanzees . Experimts tests . CriticaOverall, these results revealed a striking advantage of eyes having positive contrast polarity, namely, the eyes of both species with the uniformly white sclera and a darker iris, in the gaze-discrimination performance of both human and chimpanzee participants. Our results thus supported H1 . We also found that, although both human and chimpanzee eye-gaze directions are reliably discernible when those eyes were presented sufficiently large and bright , the human eye-gaze directions were more discernible than the chimpanzee eye-gaze particularly when those eyes were presented smaller and more shaded .Our alternative hypotheses (H2–5) cannot explain the overall patterns of our results. H2  cannot explain our results likely because it supposes clear visibility of only iris but not that of eye-outline edges, another critical feature that contributes to the visibility of eye-gaze  also se. H3 per, and sucOur results thus suggest that the visibility of human eye-gaze is primarily supported by basic color properties of the eyes, and thus by a basic perceptual mechanism shared among human and chimpanzee participants. Relatedly, there are a number of previous studies documenting the similarities in visual perception, including spectrum sensitivity, visual acuity, and contrast sensitivity, between humans and nonhuman apes  though sOne clear limitation of this study is that only a small number of chimpanzees could participate in our test conditions, which hampers the generalization of our results. Nonetheless, if the performance of the current task is supported by simple color properties of eyes and basic visual perception of great apes as argued above, our results should be replicated in other (trained) individuals and likely also in other great ape species. However, further tests are necessary to confirm this prediction. Finally, it remains unanswered whether our results are generalizable to other stimuli with some variations in sclera color, specifically given that some chimpanzee individuals have partly unpigmented (white) sclera . HoweverIn conclusion, we demonstrated that uniform whiteness in the exposed sclera enhances eye-gaze signaling. We thus provided experimental support for the gaze-signaling hypothesis despite recent criticisms on this hypothesis . HoweverStudy 1 tested 25 human adults  who had moderate to extensive experience in caretaking or studying chimpanzees . Although our human participants were mostly from similar cultural backgrounds, two related experimental studies tested participants from other cultural backgrounds , and thuStudy 2 trained 10 chimpanzees . Among them, three chimpanzees  passed all the training stages and participated in Experiment 1. Two of these three chimpanzees  participated in Experiment 2. Daily veterinary checks indicated no specific visual problems (including color blindness) that may have interfered with the execution of current experiments in our chimpanzee participants , we confirmed that including or not including them in our analysis yielded the same results. Participants sat in front of a 23-inch monitor . They placed their second- to fourth-digit fingers on the left, down, and right keys of a standard keyboard connected to the computer. With this setup, the viewing distance was about 60–70 cm. Participants were told to sit in front of the monitor as they normally would and not to move their original head position throughout the experiments.Study 2 tested chimpanzee participants in a testing room equipped with touch panels  installed with their centers 45 cm from the floor. With this position, the eye level of the chimpanzees was roughly at the center of the monitor when they sat on the floor. The monitor was installed 15 cm behind transparent polycarbonate panels, and there was a rectangle hole sized 40 × 15 cm on the panel so that chimpanzees could view the stimuli through the panel while making a touch response by inserting their arm through the hole . With thWe prepared chimpanzee and human facial images with different levels of sizes and brightness. Eyeball regions of these facial images were manipulated to have either normal or reversed contrast polarity . To creahttps://osf.io/2xny3/). The selected chimpanzee individuals included juveniles and adults of both sexes, and their sclera colors were uniformly dark (from the iris edge to the eye corner). Although some chimpanzee individuals have unpigmented spots in their sclera (The selection criteria of stimulus photographs were as follows: (1) the photographed individual oriented both head and eyes directly to the camera, (2) all eye features of the individual were clearly visible, (3) no strong shade was visible on the face, and (4) no expression was shown in the face. See the author’s online repository for the full set of chimpanzee stimuli . The cropped images were then pasted into a uniform 50% gray background sized 400 × 400 pixels. The size of each cropped facial image (for both chimpanzee and human image) was adjusted based on its iris diameter, which was set at 16 pixels (4.2–4.4 mm on the monitors used in both studies 1 and 2). This size adjustment was performed to test the effect of eye shape  independently from its absolute size and also to test the effect of white sclera independently from its exposed area size (see below for the quantification of these parameters). It should be noted that, due to these controls, our chimpanzee stimuli were presented as slightly larger than the size proportional to human stimuli because the eyeball size of humans is generally slightly larger (about 5–10%) in that of chimpanzees . To creaWe then evaluated the shape and color of the eyes in our images following a previous method . We firsFinally, we converted the facial images to various levels of sizes and brightness. Study 1 used four stimulus levels (L1–4). L1 stimuli measured 400 pixels in width  and 100% brightness , L2 stimuli measured 200 pixels in width (1/2) and 50% brightness (1/2), L3 stimuli measured 100 pixels in width (1/4) and 33% brightness (1/3), and L4 stimuli measured 50 pixels in width (1/8) and 25% brightness (1/4). These size and brightness levels were determined based on pilot experiments with two human participants (who did not participate in Study 1) so that the gaze direction of L4 stimuli was recognizable to both participants at least in one of the stimulus species with either positive or negative eyes. In Study 2, we prepared three additional stimulus levels, L1.5, L2.5, and L3.5, which were the intermediate between L1 and 2, L2 and 3, and L3 and 4, respectively, in terms of size and brightness  so that chimpanzees could move to the next stimulus level without showing substantial drops in their performances (see details about the test procedures below). Studies 1 and 2 used identical stimuli except that Study 1 presented the whole face in a 1:1 square image , while Study 2 presented only the eye region in a 4:1 rectangle image  to reduce attentional demands on chimpanzees.We made the task procedures of studies 1 and 2 as similar as possible, although several unavoidable differences existed because chimpanzees required extensive training to master the gaze-detection task. In Study 1, the task for the human participants was to indicate the direction of gaze (left/front/right) in the stimulus face presented at the center of the screen by keypress in each trial. They were instructed to answer as accurately and quickly as possible.Study 1 consisted of two experiments. All participants completed experiments 1 and 2 in this order. Experiment 1 presented stimuli with normal eye contrast polarity at L1–4 levels. Experiment 2 presented stimuli with eyes having both normal and reversed contrast polarities at L3–4 levels. Before each experiment, they completed 20 practice trials presenting L1 stimuli . Each experiment consisted of a total of 96 trials with eight blocks . In both experiments, each block presented the stimuli of the same species, and the eight blocks alternately presented chimpanzee and human stimuli. In Experiment 1, each block started with three consecutive trials presenting L1 stimuli of either species  and then increased the stimulus level every three trials; namely, 1st–3rd trials, 4th–6th trials, 7th–9th trials, and 10th–12th trials respectively presented L1, L2, L3, and L4 stimuli of either species. Thus, in Experiment 1, 12 trials presented stimuli of either species  at each stimulus level (L1–4). In Experiment 2, each block  started with six consecutive trials presenting L3 stimuli of either species and then six consecutive trials presenting L4 stimuli of the same species. The first two blocks (first and second blocks) presented stimuli of the two species with normal eye contrast polarity (each block presented one species), and then the next two blocks (third and fourth blocks) presented stimuli of the two species with reversed eye contrast polarity. The fifth and sixth blocks and the seventh and eighth blocks again presented stimuli of the two species with normal eye contrast polarity and then those with reversed eye contrast polarity. Thus, in Experiment 2, 12 trials presented stimuli of either species  at each stimulus level  in either eye contrast polarity . Each participant completed all experiments in 25–30 min. All experiments were conducted in November 2020.The number of times in which each gaze direction (left/front/right) was presented was balanced in each participant , and the number of times in which each stimulus individual was presented was also balanced both within each participant and across participants . The order of presenting the chimpanzee or human stimuli in the first block was counterbalanced across participants. The orders of gaze directions (left/front/right) and stimulus individuals were pseudorandomized so that the same gaze direction was not presented in more than two successive trials, and the same stimulus individual was not presented in any successive trials.In Study 2, the task for the chimpanzee participants was to indicate the image with averted gaze  among two other images with direct gaze  by a touch response in each trial , each session consisted of 48 trials and four blocks. Each block  presented stimuli of the same species, and the four blocks alternately presented the chimpanzee and human stimuli. Each chimpanzee performed 1–8 sessions per day depending on their motivation. Each session lasted about 10 min. Study 2 took about 8 months from August 2020 to March 2021 including both training and test periods.Training performed before these two experiments in Study 2 consisted of six training stages, and chimpanzees were trained for the task in a step-by-step manner through these stages. Training stage 1 presented the target image with no iris with the distractor images with irises . To test chimpanzees at stimulus levels higher than L1, we incremented the stimulus level by 0.5 when the chimpanzee scored above 85% in two successive sessions . The pre-test phase started from stimulus level L1 and the test phase started from stimulus level L2.5. We used stimulus levels higher than  L2.5 for the test phase because the results from Study 1 (human participants) indicated that clear performance differences between the stimulus species  emerged at stimulus levels higher than L2. To examine individuals’ performance across sessions, each individual completed a minimum of 20 test sessions. To avoid the ceiling effect, we incremented the stimulus level by 0.5 when the individual scored above 85% in two successive sessions in test trials during the test phase. Two chimpanzees (Natsuki and Hatsuka) participated in Experiment 2. The other chimpanzee (Pendesa) took more than twice as many sessions as the other two chimpanzees for training and thus was dropped from Experiment 2 . ExperimIn both experiments 1 and 2, (pre-)test sessions presenting stimulus levels higher than or equal to L1.5 consisted of 24 baseline and 24 test trials. The baseline trials presented L1 stimuli, and the test trials presented the stimuli at higher levels. Each block  presented six baseline trials consecutively and then six test trials. Thus, in each test session, 12 trials presented stimuli of either species  at the L1  or higher levels . Chimpanzees maintained high performances in baseline trials across sessions for both human and chimpanzee stimuli in the Test A1 phase , Test B phase , and Test A2 phase .As in Study 1, the number of times in which the target image (with averted gaze) was presented on each location (left/center/right) was balanced in each session , and the number of times in which each stimulus individual was presented was balanced in each session . The order of presenting chimpanzee or human images in the first block was counterbalanced across sessions. The locations of the target images and the order of presenting the stimulus individuals were pseudorandomized so that the target image did not appear on the same location in more than two successive trials, and the same stimulus individual was not presented in any successive trials. See α level adjusted for the number of individuals in the Bonferroni correction; namely, 0.05/3 in Experiment 1 and 0.05/2 in Experiment 2. For all models in studies 1 and 2, we included all possible random slope components, although we removed the correlations between random slopes and intercepts to ease the nonconvergence issues (https://osf.io/2xny3/).To test the participants’ performance differences between conditions, we ran a binomial GLMM in R (version 4.0.5). In Experiment 1 of Study 1, the model included participants’ correct response  as the response variable, stimulus species , and stimulus level (L1–4) as test fixed factors, the interaction between those test factors, block and (within-block) trial, which was nested in each block, as control fixed factors, and participant and stimulus individual as random factors see . In Stude issues . Overdis The study by Kano et al. is notable for being the first to adopt a comparative experimental approach, testing both humans and chimpanzees in a cross- and within-species design, demonstrating that uniformly white sclera enhances eye-gaze discrimination in both species. Crucially, their results support the gaze-signaling hypotheses for the evolution of particular features of the human eye but further suggest that uniformly white sclera are critical for eye-gaze discrimination when visibility conditions are poor. public reviews designed to be posted alongside the preprint for the benefit of readers; ii) feedback on the manuscript for the authors, including requests for revisions, shown below. We also include an acceptance summary that explains what the editors found interesting or important about the work.Our editorial process produces two outputs: i) Decision letter after peer review:eLife. Your article has been reviewed by 2 peer reviewers, including Ammie K Kalan as the Reviewing Editor and Reviewer #1, and the evaluation has been overseen by Detlef Weigel as the Senior Editor. The following individual involved in review of your submission has agreed to reveal their identity: Kai R Caspar (Reviewer #2).Thank you for submitting your article "Experimental evidence for the gaze-signaling hypothesis: White sclera enhances the visibility of eye- gaze direction in humans and chimpanzees" for consideration by The reviewers have discussed their reviews with one another, and the Reviewing Editor has drafted this to help you prepare a revised submission.Essential revisions:Both reviewers found this study well executed with carefully designed experiments and transparent reporting of procedures. However a number of key issues require some attention during revisions:1) Can you clarify and spend more time in the introduction explaining the general aim of your study followed by the justification and rationale for your experimental design given each one of your hypotheses. At the moment the hypotheses are encountered without a clear, overarching picture of the study's aims. Some hypotheses/tests are also not clearly explained. Why for example was inverted eye colour tested? .2) Contextualize your results and findings better given that other nonhuman primates also have depigmented sclera and the fact that chimpanzees' dark sclera may not have been the ancestral condition (see Reviewer 2's detailed concerns). Can the authors spend more time to discuss potential alternative explanations given the variation observed in sclera colouration in other great apes?3) Regarding your stimuli of inverting colours, the design procedure does not match the stimuli shown in Figure 1. If there was an inversion of iris and sclera color (including contrast and hue), then the inverted chimpanzee would need to have an amber-colored sclera and a blackish iris. Yet, the inverted chimp model apparently has a human-like white sclera and retains the amber-colored iris. Additionally, the pupil colors were also inverted for both species. Can you please explain this discrepancy and provide a clear explanation as to why these stimuli were edited in this manner, which hypotheses specifically they relate to, and whether you controlled for contrast and hue in this inverted/edited stimuli for the chimps given that the contrast values for the humans were equal in the two conditions. Please also provide additional examples of stimuli in the methods to aid clarification.4) Clarify the GLMM code by adding the R script to aid transparency. It was not clear for example what the exact response variable was in your models.5) Expand upon your limitations of the study section by explicitly stating the inability to generalize for chimpanzees given the low sample size and specific experience with touchscreens these chimps have, and the need for a cross cultural sample of human participants as well.6) Clarify the differences between eye gaze and glancing/head direction with respect to communication and cooperation , and the potential implications/limitations of this for your experimental design and its interpretations.Reviewer #1 (Recommendations for the authors):Overall I find the study by Kano and colleagues will be a solid contribution to the literature on this important topic.Reviewer #2 (Recommendations for the authors):IntroductionThere is some confusion in the primate cognition literature when it comes to the differentiation between glancing/eye gaze and gazing/head direction. From my impression, the authors are perfectly aware of this distinction and refer to it in several sections of the manuscript. Still, they do not adequately differentiate it in the text. For instance, in the first section of the introduction, they refer to "eye gaze" in humans, then switch to "gaze" in great apes without indicating that two fundamentally different signals are described. Later on, the authors equate "eye gaze" with "gaze" (l. 65) which should not be done to avoid further confusion. The clarity of the text would be significantly improved by briefly stating the differences between the two phenomena and how they are referred to throughout the text.l. 52: Please note that the conjunctiva, which contribute to the dark-eyed phenotypes of many primate eyes, is also depigmented in humans.l. 56: "eye shape" is an ambiguous expression. What exactly is meant here?l. 64: perhaps replace "our" with "a".l. 83: Please be precise when referring to "color". The studies you cite here did, for instance, not study hue, but exclusively relied on differences in gray values. In the supplements, you refer to the lab color space that I am unfamiliar with (and probably many readers as well). Does it allow a differentiation between  contrast and hue? Furthermore, chimpanzee eyes and human eyes indeed significantly deviate from each other in absolute irido-scleral contrast. They do not differ in relative iris luminance, which is way of iridoscleral contrast quantification that should not be applied for interspecific comparisons .Figure 1: I'm not exactly sure if I understood what you mean by inverting eye color "without affecting the iris-sclera color contrast". The inverted chimpanzee figure does not look color inverted to me (shouldn't it have an amber-colored sclera and a black iris?).Please also note that you inverted pupil color and explain why you did it. This decision leads to visibility of the pupil in the inverted chimp picture but not in the one of the inverted human. This might have implications for the experimental results. I suggest to at least briefly mention this issue.Just out of curiosity: Is there a specific rationale behind the order in which you present the hypotheses? Why is the core hypothesis not #1?ResultsThe study impressively demonstrates that chimpanzees have enormous difficulties to differentiate between glancing conditions, as shown by the extensive training needed to reliably accomplish this task and the high percentage of drop-outs. It has been prominently argued recently, that chimpanzee eyes are optimized to convey eye-gaze cues and that the role of glancing in chimpanzee social behavior has been underestimated . I believe it is important to point out how the new results challenge these proposals, which – if true – would bear important ramifications for chimpanzee communication.You report only minor effects of eye shape – wouldn't this be expected, given the comparatively modest displacement of the iris relative to a direct glance condition is in your test stimuli?Discussionl. 237: Please note that critics of the gaze-signaling hypothesis do not deny that the human eye is more conspicuous than that of chimpanzees . The key problem of this hypothesis is that it assumes a functional link between eye pigmentation and socio-cognition although there is no evidence for this. Humans are the only species in which this connection has been shown and it is not clear, whether this is a coincidental correlation. For instance, the hypothesis cannot explain extensive scleral depigmentation in non-human primates such as orangutans and howler monkeys. I would suggest to be more transparent when it comes to discussing recent criticisms of said hypothesis and how the results from this paper can add to the debate.Methodsl. 430: "Training 431 stage 1 presented the target image with no iris with the distractor images with irises (in direct gaze)." Was pupil color affected as well? Perhaps an example of these test stimuli would be a good addition to the supplements, to give readers a better impression. Essential revisions:Both reviewers found this study well executed with carefully designed experiments and transparent reporting of procedures. However a number of key issues require some attention during revisions:1) Can you clarify and spend more time in the introduction explaining the general aim of your study followed by the justification and rationale for your experimental design given each one of your hypotheses. At the moment the hypotheses are encountered without a clear, overarching picture of the study's aims. Some hypotheses/tests are also not clearly explained. Why for example was inverted eye colour tested? .Accordingly, we substantially expanded our introduction section to better frame our hypotheses and experimental rationales. Please see our new introduction section (page 2-9).Regarding the “inversion of eye color”, we actually should have said the “reversal of contrast polarity of eyes”, an experimental manipulation adopted in a related experimental study . See below for the details about this point.2) Contextualize your results and findings better given that other nonhuman primates also have depigmented sclera and the fact that chimpanzees' dark sclera may not have been the ancestral condition (see Reviewer 2's detailed concerns). Can the authors spend more time to discuss potential alternative explanations given the variation observed in sclera colouration in other great apes?Accordingly, we also substantially expanded our Discussion section to better relate our results to those recent morphological studies on great ape eye color. Please see our new Discussion section (pages 15-18).Also, in this revision, we can better clarify our hypotheses, rationales, and interpretations by referring to one most recent morphological study on great ape eye color . Although our experimental study was independently performed from this related study, we have built some of our experimental designs based on the results from this related study. Yet, we could not refer to it extensively in our previous manuscript because this related study has not been out for a while (we apologize for any unclarity of our previous manuscript arising from this publication timing issue). The results from this related morphological study are complementary to those from this experimental study. We summarized the results from this related study in the introduction section, lines 91-104.3) Regarding your stimuli of inverting colours, the design procedure does not match the stimuli shown in Figure 1. If there was an inversion of iris and sclera color (including contrast and hue), then the inverted chimpanzee would need to have an amber-colored sclera and a blackish iris. Yet, the inverted chimp model apparently has a human-like white sclera and retains the amber-colored iris. Additionally, the pupil colors were also inverted for both species. Can you please explain this discrepancy and provide a clear explanation as to why these stimuli were edited in this manner, which hypotheses specifically they relate to, and whether you controlled for contrast and hue in this inverted/edited stimuli for the chimps given that the contrast values for the humans were equal in the two conditions. Please also provide additional examples of stimuli in the methods to aid clarification.per se). Please also note that the visibility of eye-gaze directions depends on the visibility of both iris and eye-outline edges, not that of only iris or pupil. To clarify this aspect, we added Figure S1.We apologize for this confusion and our insufficient explanation for the rationales. Please note that we did not swap the color of the iris and sclera in the eye image but reversed the contrast polarity of the eye image  following Ricciardelli et al., (2000). One advantage of our method is that we could change only contrast polarity but not any color differences within the eye image, namely the iris-sclera and pupil-iris color differences . Please understand that we cannot do this for our human stimuli due to the difficulty in obtaining permission to publish human faces online, but the original images can be seen in the published dataset .4) Clarify the GLMM code by adding the R script to aid transparency. It was not clear for example what the exact response variable was in your models.Accordingly, we added Table S1 detailing R formulas.5) Expand upon your limitations of the study section by explicitly stating the inability to generalize for chimpanzees given the low sample size and specific experience with touchscreens these chimps have, and the need for a cross cultural sample of human participants as well.Accordingly, we added a paragraph stating the limitation of our study. Please see lines 323-337.We clarified in our method section that the results from two related experimental studies  are complementary to our results because these studies primarily tested human participants from other cultures (lines 105-120).6) Clarify the differences between eye gaze and glancing/head direction with respect to communication and cooperation , and the potential implications/limitations of this for your experimental design and its interpretations.We added this explanation in the first paragraph of our introduction section (lines 56-60).Thank you very much for this helpful summary.Reviewer #2 (Recommendations for the authors):IntroductionThere is some confusion in the primate cognition literature when it comes to the differentiation between glancing/eye gaze and gazing/head direction. From my impression, the authors are perfectly aware of this distinction and refer to it in several sections of the manuscript. Still, they do not adequately differentiate it in the text. For instance, in the first section of the introduction, they refer to "eye gaze" in humans, then switch to "gaze" in great apes without indicating that two fundamentally different signals are described. Later on, the authors equate "eye gaze" with "gaze" (l. 65) which should not be done to avoid further confusion. The clarity of the text would be significantly improved by briefly stating the differences between the two phenomena and how they are referred to throughout the text.Accordingly, in the first paragraph of our introduction, we clarified this point (lines 56-58).l. 52: Please note that the conjunctiva, which contribute to the dark-eyed phenotypes of many primate eyes, is also depigmented in humans.Noted, although we do not have this part anymore in our revision.l. 56: "eye shape" is an ambiguous expression. What exactly is meant here?Accordingly, we detailed this in our expanded introduction section (lines 83-104).l. 64: perhaps replace "our" with "a".Addressed.l. 83: Please be precise when referring to "color". The studies you cite here did, for instance, not study hue, but exclusively relied on differences in gray values. In the supplements, you refer to the lab color space that I am unfamiliar with (and probably many readers as well). Does it allow a differentiation between  contrast and hue? Furthermore, chimpanzee eyes and human eyes indeed significantly deviate from each other in absolute irido-scleral contrast. They do not differ in relative iris luminance, which is way of iridoscleral contrast quantification that should not be applied for interspecific comparisons .We detailed CIELAB color space in lines 464-467. Kano et al., (in press) used this color space to code both lightness  and chromaticity components of great ape eye colors. This current study employed the same method to code the eye colors of stimuli. CIELAB color space is designed as a perceptual uniform color space for humans and is considered applicable to nonhuman primates with human-like trichromatic vision.Figure 1: I'm not exactly sure if I understood what you mean by inverting eye color "without affecting the iris-sclera color contrast". The inverted chimpanzee figure does not look color inverted to me (shouldn't it have an amber-colored sclera and a black iris?).Please also note that you inverted pupil color and explain why you did it. This decision leads to visibility of the pupil in the inverted chimp picture but not in the one of the inverted human. This might have implications for the experimental results. I suggest to at least briefly mention this issue.per se.As noted earlier, in our stimulus manipulation, we reversed the contrast polarity of the eye images but did not just swap the iris and sclera colors. Please note that the reversal of the contrast polarity of the eye image does not change the iris-sclera and iris-pupil color differences (lines 144-146) and thus the conspicuousness of iris or pupil We added Figure S4 to clarify our stimulus-making procedures.Just out of curiosity: Is there a specific rationale behind the order in which you present the hypotheses? Why is the core hypothesis not #1?True. It should be easier to understand in that way. Addressed.ResultsThe study impressively demonstrates that chimpanzees have enormous difficulties to differentiate between glancing conditions, as shown by the extensive training needed to reliably accomplish this task and the high percentage of drop-outs. It has been prominently argued recently, that chimpanzee eyes are optimized to convey eye-gaze cues and that the role of glancing in chimpanzee social behavior has been underestimated . I believe it is important to point out how the new results challenge these proposals, which – if true – would bear important ramifications for chimpanzee communication.within the face (mainly due to the iris-sclera color difference). However, due to the lack of clarity of eye-outline edges in the nonhuman eye (mainly due to dark or graded/patchy sclera colors), their eye-gaze directional cues are less clearly visible compared to those of humans. We summarized these findings in our introduction section (lines 91-103).Kano et al., (in press) commented on Perea-Garcia (2019). Briefly, this morphological study found that the eye regions of nonhuman great apes are as salient as those of humans You report only minor effects of eye shape – wouldn't this be expected, given the comparatively modest displacement of the iris relative to a direct glance condition is in your test stimuli?This is a good point. However, previous eye-tracking studies measuring both species’ eye movements under naturalistic conditions reported that the majority of eye positions fall within 20 degrees in both species . We mentioned this in lines 289-295.Discussionl. 237: Please note that critics of the gaze-signaling hypothesis do not deny that the human eye is more conspicuous than that of chimpanzees . The key problem of this hypothesis is that it assumes a functional link between eye pigmentation and socio-cognition although there is no evidence for this. Humans are the only species in which this connection has been shown and it is not clear, whether this is a coincidental correlation. For instance, the hypothesis cannot explain extensive scleral depigmentation in non-human primates such as orangutans and howler monkeys. I would suggest to be more transparent when it comes to discussing recent criticisms of said hypothesis and how the results from this paper can add to the debate.This is also a very good point. As noted earlier, we clarified this in the limitation section of our discussion (line 323-337).Methodsl. 430: "Training 431 stage 1 presented the target image with no iris with the distractor images with irises (in direct gaze)." Was pupil color affected as well? Perhaps an example of these test stimuli would be a good addition to the supplements, to give readers a better impression.Accordingly, we added the complete set of our chimpanzee stimuli in our online repository (https://osf.io/2xny3/?view_only=b03f2ee4adf549aea09d8df5ab88f126), and moreover also the examples of our training stimuli in Figure S5.


Introduction of new technologies into cervical screening programmes has allowed more efficient programmes with less resources. We present an overview of screening technologies introduced into the Cervical Screening Wales programme and their evolution over time.Data from the programme’s statistical report were used to evaluate its performance over a 17-year period between 2001/02 and 2017/18.The introduction of liquid-based cytology has had a substantial impact on reducing inadequate sample rates and on increasing the positive predictive value of cytology. Inadequate rates have increased following the implementation of human papilloma virus testing as a triage test for cytology. Further knock-on effects on standard reporting ranges are expected following the introduction of human papilloma virus testing as the primary screening test. New performance standards have been introduced to better reflect the performance of the programme at a time when disease prevalence is expected to fall as women vaccinated against human papilloma virus reach screening age.Improvements to this cervical cancer screening programme as illustrated through performance indicator ranges suggest a major role played by technology. By 1967, cervical screening had been introduced across the whole UK National Health Service (NHS). It took two more decades before evidence that screening reduced the incidence of and mortality from cervical cancer became irrefutable.24 In 1988, the UK introduced a computerised call/recall system and recommended that women aged 20 to 64 be screened every three to five years.6The Pap test  was developed by George Papanicolaou in the early 1940s.7 CSW would be responsible for the cervical screening programme, including management and co-ordination, call and recall arrangements, cytology sample taking, cytology services, histology services and colposcopy services.810Although call/recall was introduced in Wales from 1988, a unified screening programme did not come into force until 1999 when Cervical Screening Wales (CSW) was launched by Welsh Health Minister, Jon Owen Jones.12 These are called performance standards. Given that cervical cytology was introduced into routine practice without evidence from randomized controlled trials, there is no ‘gold standard’ against which performance can be compared. This makes setting performance standard indicators for cervical screening particularly difficult.All organised screening programmes have quality measures to assess and maintain high standards.Since 1998 there have been several technological advances introduced by CSW. This review uses data from the Welsh cervical screening programme to evaluate its performance over a 17-year period between 2000 and 2017. The focus is on four performance indicators: inadequate sample rates, proportion of adequate tests reported as high-grade dyskaryosis, sensitivity to high-grade disease, and the positive predictive value (PPV) of high-grade dyskaryosis for histologically confirmed CIN grade 2 or worse disease. The aim is to present a qualitative description of the evolving programme and a quantitative audit of trends in standard reporting ranges over a 17-year period between 2001/02 and 2017/18.Achievable standards, Benchmarks for reporting and Criteria for evaluating cervical cytopathology”  by the English NHS Cervical Screening Programme13 that standard ranges for cervical cytology were established. In fact, before 1995, there were few explicit performance standards for cytology sample takers and no coordinated system for monitoring performance.Although the launch of the organised screening programme in 1988 drew attention to quality issues, training requirements and the importance of early and effective treatment, it was not until the publication in 1995 of the document “Defining the optimal range for cervical screening performance standards is challenging as it depends on the relative value given to a high specificity or a high sensitivity. Performance ranges in the first ABC Report were derived from a survey of two consecutive years’ results from 12 selected laboratories in England. In the second ABC Report, the standards were reviewed as more years of data become available, but performance ranges were still based on reference ranges from laboratories in England. Hence, performance indicators concentrate on identifying outliers in the data and subjecting them to scrutiny, ensuring a more even service across the country and identifying those laboratories where further investigation may be required. These indicators were adopted by CSW from 1999 onwards.14 document to reflect changes to the national programme, including the use of liquid-based cytology and the implementation of human papilloma virus (HPV) triage. The new standards were designed to produce a more uniform national programme, enabling it to operate at an optimal ratio of maximum benefit to minimum harm.15 The Welsh programme began reporting these new values from 2014/15 onwards.Performance indicators were updated in the latest version of the ABC (3rd version)A summary of performance indicators and how these have changed over time can be found in proportion of adequate tests reported as inadequate,proportion of adequate tests reported as moderate or worse dyskaryosis,positive predictive value (PPV) – proportion of women referred with moderately/severe dyskaryosis whose biopsy is reported as CIN2+, andsensitivity of primary screening – proportion of women with a CIN2+ who had a cytology result of moderate/severe dyskaryosis.Referral value (RV) – number of women referred to colposcopy to detect one CIN2+.Mean cervical intraepithelial neoplasia score (MCS) – a method to summarise the distribution of detected CIN cases as a single figure.Abnormal predictive value (APV) – calculates the percentage of samples reported as borderline or low grade that led to referral and subsequent diagnosis of CIN2 or worse.High-risk (HR) HPV-positive rate for borderline/low-grade samples.The four new performance standard measures introduced in ABC3 are:16 It was therefore recommended that all slides considered negative or inadequate be subject to a rapid (60 s) re-screen.16“Rapid re-screening” was first proposed as a method for routine quality control of primary screening (using cytology) in 1995. Rapid re-screening of all tests was recommended over selective double screening of 10% of negative samples at normal speed because it was shown to be as sensitive in preventing false negatives.8 CSW standardised rapid review across laboratories and embedded it into good practice.At the time of the introduction of the Welsh screening programme (in 1999), all laboratories in Wales operated a system of rapid review of all slides declared normal or inadequate at initial screen (in England 96% of laboratories used the technique at the time). However, the time spent reviewing each slide varied between laboratories, and at least two laboratories seeded known positive slides into those to be rapid reviewed as a test of the effectiveness of the process.17 Additionally, evidence suggests that rapid pre-screening is more sensitive in LBC than in conventional cytology.18 To date, there are two major liquid-based cytology platforms: ThinPrep® (Hologic) and SurePath™ (Becton Dickinson). Both technologies have the necessary regulatory approvals to be used within UK screening programmes but they use different preservative fluids and employ different methodologies in sample preparation, so laboratories must choose one.Liquid-based cytology  has been favoured over conventional cytology because it leads to lower rates of inadequate samples.19 and a full roll-out of the technology was authorised in February 2004 with a concomitant training programme for laboratory staff and cytology sample takers which was completed in June 2005. However, CSW decided that, for the full conversion, SurePath™ technology would be adopted nationally. The last laboratory to convert to LBC did so by January 2006. Since then all cervical smears taken in Wales have been processed using LBC technology.10In Wales, a pilot across four laboratories was set up in 2001 using ThinPrep® to assess whether LBC should be implemented fully across Wales. The pilot was successful20 The system analyses images to detect squamous carcinoma and adenocarcinoma, and their precursor lesions, in cervical cytology preparations.21 The main benefit is workload reduction. A manual quality assurance check prior to a negative report being issued is only required for about 20% of cervical cytology samples identified as negative by the technology.Computer-assisted technology  became operational in Wales in October 2012.Once HPV primary testing is fully rolled out and the cytology workload is substantially reduced, rapid review and no further review technology may become obsolete.22 At least 13 HPV sub-types have been identified as high risk for causing cancer. Around 70% of cervical cancers are caused by just two types, HPV 16 and 18.23High-risk HPV, a common sexually transmitted infection, is the underlying cause of cervical cancer.25 The European Union as of 2015 recommended that HPV-based screening should be the preferred primary screening method for women aged over 30 years.26There is strong evidence that testing for the presence of HR-HPV virus is more effective at protecting against invasive cervical cancer than cervical cytology.27 and a pilot study involving 20% of the population in Wales, as of September 2018, HPV primary testing was introduced into the Welsh screening programme for women aged 25–64 years.HR-HPV testing was introduced in September 2014 to Wales as triage for borderline and mild cytology. However, full implementation did not occur until May 2016. Following a full economic evaluation28 In September 2015, the first vaccinated catch-up cohorts reached the age of 25 and became eligible for screening. The first cohort of women vaccinated at ages 12–13 will enter screening in 2020. Since September 2011, the quadrivalent vaccine (Gardasil) has been used.Vaccination against HPV types 16 and 18, with the bivalent (Cervarix) vaccine, was rolled out nationally in 2008 to girls aged 12–13 with a catch-up programme for those aged 15 to 18.29 This means that a woman screened at age 60 years will now be exited, whereas previously she would have been invited again at age 63. As of April 2019, there were no plans to extend the screening intervals in women receiving HPV primary testing in Wales.30From 1999 (until September 2013), screening was offered to women aged 20–64 at a three-yearly recall interval. In 2013, the Welsh Government announced that, in line with recommendations made by the UK National Screening Committee, the age range covered by Cervical Screening Wales and the frequency of invitation would change in response to evidence that screening women under the age of 25 is not effective at preventing cervical cancer, and the lack of evidence to suggest that women over the age of 50 need to be screened more frequently than once every five years. From the 1st of September 2013, women born after 1 September 1993 have been invited for cytology tests at age 25 and any woman aged between 50 and 64 who attends screening is re-invited every five years rather than every three years.In 1999, there was considerable variation in both organisation and performance of the screening programme among cytology and histology laboratories. At the time, cervical cytology from Wales was processed and read at 13 laboratories in Wales and 3 in England. Only 8 out of the 13 in Wales had full and unconditional accreditation by the Clinical Pathology Accreditation (CPA) body.8 These standards mandated that all laboratories be fully CPA accredited, all terminology for reporting should be British Society for Clinical Cytology (BSCC) terminology,31 and that laboratories be monitored against standard reporting ranges. To ensure standards were maintained, the minimum number of hours staff could work without a break and number of slides that staff needed to review per year were also specified.Following the launch of CSW, standards were set out to which all cytology and histology laboratories should aim to be performing.32 Given that reporting of HPV results can be automated and will lead to a significant fall in cytology workload, the four remaining laboratories in Wales were consolidated into one (at Magden Park) in September 2018.33Standardisation of laboratory practices, including standardisation of rapid re-screening, allowed for the 13 original laboratories in Wales when CSW was formed to be consolidated into 11 laboratories by 2001. A further reorganisation of pathology services resulted in the 11 laboratories being consolidated into seven in 2011/12. A year later, the services consolidated further into four laboratories.15 These data are summarised yearly in statistical reports publicly available for the 2001/02 financial year onwards. To illustrate the effect of quality assurance and new technologies on performance standards, data from the CSW statistical reports are summarised graphically for a 17-year period between the financial years 2001/02 and 2017/18 in 34 The data for 2018/19 include results separately for four laboratories . However, given that this was a key transition year for the programme, the results are mentioned in the text although not displayed in the figures.Data from the annual statistical returns (known as KC61 returns) are used to evaluate performance standards for the CSW programme.The impact of implementing liquid-based cytology is best observed in the proportion of inadequate tests reported over time in Wales. The overall inadequate rate in Wales in 2001/02 was 8.6%. From 2004/05, when the roll-out of LBC was initiated, the inadequate rate fell to 2.6% and by 2006/07 when the roll-out was completed, the rate dropped to under 2%  was 1.0–4.3% at a time when only 5% of the population were being tested with HPV as a primary test.36Since the roll-out of HPV triage, cytology inadequate rates in Wales have slowly been increasing to an average of 3.6% in 2017/18 (36 (76.7–92.3%) and in a recent systematic review of 27 studies where the PPV  was on average 77.5%.37A similar situation to that observed with the proportion of inadequate slides can be observed with the PPV of moderate or worse cytology for a diagnosis of CIN2 or worse  and the referral value (RV) (It has been well documented that some areas of the UK have a higher incidence of pre-cancerous disease than others.lue (RV) . To undelue (RV) . Similarlue (RV) . For con34 A peak is observed in 2008/09 and 2009/10 most likely related to the Jade Goody effect,41 which resulted in more women with a previous abnormality or who were lapsed attending screening. From 2014/15, when HPV triage was introduced, there has been a slight increase in the proportion of tests reported as moderate or severe dyskaryosis; however, this did not exceed 1.5% by 2017/18. The 2018/19 figures show that 2.6% of tests were reported as high-grade. This huge increase is expected when one considers that most of the cytology samples taken are triggered by a positive HPV test result. The proportion of tests reported as high-grade is likely to be further affected by the decreasing prevalence of vaccine-associated HPV types leaving less carcinogenic HPV types to be detected. There is also concern that the cytology workforce may become deskilled in an era when high-grade cytology becomes rare.In Wales, from 2001/02 to 2017/18, on average 1.3% of adequate tests were reported as moderate or severe dyskaryosis  do not allow for stratification of performance standards by age or screening interval, both of which could account for the changes observed.Continuous changes to the screening programme have made quality assurance difficult. In the coming years, performance indicators will be the first available statistics on which to evaluate the response of organised programmes to the rapidly changing times. Although the data presented here are specific to the Welsh screening programme, the impact of liquid-based cytology, HPV testing and vaccination on performance indicators is generalisable to other settings where organised screening is offered.As has been illustrated here, cervical screening performance measures are susceptible to changes in technology, laboratory capacity and disease prevalence. Given that most screening programmes are now using HPV as the primary screening test and that vaccinated women are reaching screening age, over the coming years, careful monitoring of programme standards will be more important than ever. In addition, screening programmes should prepare mitigation strategies such as extending screening intervals, introducing new triage tests, and improving training and resilience of the workforce.


Tumor-induced osteomalacia (TIO) is a rare, acquired condition of phosphate wasting due to phosphaturic mesenchymal tumors. Because the incidence and prevalence of TIO is unknown, we conducted an observational cohort study using national Danish health registers for the period 2008 to 2018 to obtain such information. The study also aimed to describe the demographics of the TIO population and the prognosis. The operational definition was based on hypophosphatemia or adult osteomalacia diagnoses, combined with prescriptions used in the initial management and procedures consistent with advanced imaging used for locating tumors. The incidence of TIO in Denmark was found to be below 0.13 per 100,000 person years for the total population of the country and 0.10 per 100,000 in adult-onset disease. The prevalence of TIO was estimated to be no more than 0.70 per 100,000 persons for the total population and 0.43 per 100,000 in adults. In 2018, there were a maximum of nine new cases of TIO in Danish adults. Mortality was low but few patients fulfilled the protocol cure criterion during the observation period. TIO has no ICD-10 code and limitations to the study include lack of information on serum biochemistry and on the use of phosphate supplements. Strengths include the use of long-term longitudinal, national hospital and prescription data from a country with universal healthcare. Given the very small patient population with TIO and the known delay to diagnosis and cure, management of patients with suspected TIO should be centralized.The online version contains supplementary material available at 10.1007/s00223-021-00843-2. Tumor-induced osteomalacia (TIO) is a rare, acquired condition of phosphate wasting due to FGF23 secreting tumors . Excess Biochemically, patients with TIO typically present with an unusual combination of low serum phosphate, normal serum calcium levels, raised alkaline phosphatase and normal or elevated PTH. Measuring 1,25(OH)2D and finding it low further strengthens the suspicion of TIO but the essential step in the diagnosis is demonstrating inappropriately high renal excretion of phosphate, evident as a low TmP/GFR measured in a two hour urine collection in a fasting subject. Alternatively, %TRP can be measured. In a normal subject, TmP/GFR will be high in the presence of a low serum phosphate level whereas it is low in FGF23 driven hypophosphatemia including TIO [Surgical removal of the tumor is the definitive treatment for TIO. Medical treatment to manage the chronic hypophosphatemia is required in the short-term management of patients up to the point of successful surgery and in the long term in patients where tumors cannot be identified and excised or eradicated by other means.Despite the rise in the volume of publications on the pathophysiology and management of patients with TIO over recent years, there is a fundamental lack of knowledge about the true prevalence and incidence of TIO . The chaGiven the non-specific clinical presentation of the patients it must be expected that coding in routine data can change during the assessment of the patient. Hence, some patients who are initially coded with a broader ICD-10 code that is at first compatible with TIO will later be assigned a more specific code once they have completed their diagnostic workup. For example when the inherited phosphate wasting disorder XLH , 9 has bIn order to address these gaps in knowledge, we conducted a register-based study on Danish national data to determine the incidence and prevalence of TIO in Denmark over a ten-year period and describe the demographics of TIO patients. The Danish health databases provide a unique opportunity to provide reliable estimates of TIO incidence, prevalence and prognosis.Describe the epidemiology of TIO in Denmark in terms of incidence, prevalence, demographics and prognosis using national registers.The study was designed and reported in accordance with the STROBE guidelines for observational studies . Based oObservational, open cohort study using national data from a country with universal healthcare.Danish residents in the period 2007–2018, both genders, any age, with a sub-analysis done for adult-onset disease (age 18 or over). Only eligible for inclusion in incidence rate and prevalence calculations for calendar years that were preceded by a full calendar year of residence in the country. Observations were truncated when the subject was no longer resident in Denmark, at death or on the 31st of December 2018, whichever occurred first.The National Hospital Discharge Register (Landspatientregistret) contains all diagnostic codes and treatments for inpatients  and outpatients  . It contHypophosphatemia (ICD-10 E833A) or Vitamin D resistant rickets (E833B) or Other adult osteomalacia (M838), after exclusion of XLH / Familial Hypophosphatemia (E833A1). This is abbreviated group A in the results.All persons with an ICD-10 encounter for also had advanced imaging suggestive of TIO but had not filled prescriptions for one-alpha-hydroxylated vitamin D that would have placed them in the Definitive TIO category (see below). This addressed the possibility that patients could have received one-alpha-hydroxylated vitamin D by hand in outpatient clinics without requiring a prescription. We therefore created the additional operational definition “Possible TIO with advanced imaging”, abbreviated group B in the results). Following reviewer concerns we also investigated the presence of multiple myeloma—with the potential of hypophosphatemic osteomalacia—or drug induced adult-onset Fanconi syndromes.In addition, in a post hoc analysis we identified persons meeting this criterion who also filled prescriptions for one-alpha-hydroxylated vitamin D , after exclusion of other indications. The case definition requires patients not to have consulted with CKD or hypoparathyroidism (± 1 year of the index date) or been treated with iron infusions. Abbreviated group C in the results.Cases meeting the Possible TIO definition (see above) who Cases meeting the Possible TIO definition and the advanced imaging criterion and who have filled prescriptions for one-alpha-hydroxylated vitamin D.Incidence rates were calculated as the number of new cases with contact episodes within a calendar year meeting each of the operational definitions for TIO (see above), who did not have a contact episode for TIO in the preceding calendar year. We used 2007 as a run-in year to allow incidence rate calculations from 2008 and on. The denominator is the number of person years at risk  in the calendar year. Rates were expressed as new cases per 100,000 person years.period contact prevalence with the numerator calculated as follows: The number of persons with at least one contact episode for TIO  in the calendar year. Denominator: Number of persons at risk . Prevalence was expressed as cases per 100,000 population.Disease prevalence was calculated as the Not applicable.N = 5, Fig. Patients lacking a Danish ID number were not included in the analysis  met the protocol case definition of definitive TIO, i.e. the required combination of diagnosis code, advanced imaging and prescriptions filled for one-alpha-hydroxylated vitamin D. Statistics Denmark rules for data privacy do not permit analysis of groups with fewer than five members so additional details cannot be presented for this subcategory. The study identified 15 cases of possible TIO who also underwent advanced imaging, corresponding to 0.024 per 100,000 patient years. The imaging used was F-18-FDG in 14 cases and Ga-68-DOTATOC in one case. A further 67 cases met the definition of probable TIO after exclusion of CKD and iron infusion as competing causes  varied over the duration of the study with 2015 having the highest contact prevalence for probable TIO  and 2018 the highest contact prevalence for possible TIO with advanced imaging (data not shown). For the most recent year, 2018, there were 27 patients—17 women and 10 men—still consulting after either possible TIO with advanced imaging (N = 7) or the case definition of probable TIO (N = 22 as categories overlap), corresponding to a combined contact prevalence of 0.47 per 100,000 persons.The N = 6) or a probable TIO after excluding competing causes (N = 10), for a combined contact prevalence of 0.325 per 100,000 persons.In the sub analysis restricted to subjects aged 18 or over, there were 15 cases consulting in 2018 after either a possible TIO with advanced imaging  was under five cases—the lowest number for which we are permitted to present data under Statistics Denmark regulations—corresponding to a prevalence below 0.008 per 100,000. A more detailed analysis including upper boundary estimates—advanced imaging and/or one-alpha-hydroxylated vitamin D without a competing indication—found an incidence rate of 0.17 per 100,000 for 2018 and 0.13 for the full study period, with a 2018 upper boundary prevalence of 1.25 per 100,000 and a contact prevalence of 0.47 per 100,000. The incidence rates found increased relatively little over time with 2018—about 25% from 2008 to 2019—but prevalence increased due to low mortality and few recorded instances of tumor surgery or radiotherapy in Denmark for this population.This study confirms that the incidence and prevalence of TIO in Denmark is very low, even if applying upper boundary estimates that include patients who may have TIO but do not meet the operational case definition in full. In brief, the prevalence of The low number of cured cases in the present report may seem at first surprising given the theoretically reversible nature of this condition. However, findings should be viewed in the context that cohort inclusion over a 10-year period means that half the cases have less than 5 years of follow-up after diagnosis. The reported US experience –16 is thWe noted that an unexpectedly high proportion of potential cases were under the age of 18 at the time of meeting the operational diagnosis definition. Though TIO has been reported in children as young as 3 years of age , 18, thiThe adult onset upper boundary estimator found an incidence rate of 0.10 per 100,000 person years for the full study period, a population prevalence of 0.43 per 100,000 persons and a contact prevalence of 0.25 per 100,000 persons Below is the link to the electronic supplementary material.


Background and purpose — Surgical treatment is still the mainstay of care even in very frail elderly hip fracture patients. However, one may argue whether surgery is in the best interest of all patients. We elucidated mortality rates of nonoperative management (NOM) of a hip fracture after shared decision-making in a cohort of very frail elderly patients.Patients and methods — Orthogeriatric patients (age > 70 years) admitted with a hip fracture between 2011 and 2019 were included. In the presence of fragility features the motivation for surgery or NOM was supported by advance care planning (ACP) and shared decision-making through geriatric assessment. Mortality rates after NOM were assessed and also presented for the remaining surgical group for reference.Results — In 1,279 out of 3,467 patients, geriatric assessment was indicated and subsequently 1,188 (93%) had surgery versus 91 (7%) NOM. The motivation for NOM was based on patient and family preferences in only 20% of patients, medical grounds in 54%, and a combination of both in 26%. The 30-day and 1-year mortality in the frail NOM group was 87% and 99% respectively, whereas this was 7% and 28% in the surgery group. No statistical comparison between groups was performed due to profound bias by indication.Interpretation — This study provides further insight into the predictable and high short-term mortality after NOM in carefully selected very frail elderly hip fracture patients. This information may help to consider NOM as an alternative treatment option to surgery when no significant gain from surgery is anticipated. The incidence of hip fractures in frail patients is rising due to an increase in life expectancy and cumulative comorbidities Kanis . In partFrailty is negatively associated with quality of life after a hip fracture and may require tailored treatment, especially in patients with a short life expectancy and anticipated postoperative functional decline  is limited. For example, 30-day and 1-year mortality rates after NOM ranging from 5–65% and 30–95% have been reported , mobility, living situation, cognitive status (dementia), type of fracture, and type of surgery.Reports from the shared-decision consultation resulting in a choice for NOM were reviewed. The reason for NOM was scored independently by 2 authors (HW and DT) as (1) based on patient and family preferences, (2) obvious medical grounds with unacceptable high perioperative risk, or (3) a combination of both. In the case of disagreement consensus was subsequently achieved by discussion between both authors.If applicable, date of death was obtained from the medical records or from the Dutch Personal Records Database, which contains personal data of people who live in the Netherlands. Subsequently 30-day mortality and 1-year mortality rates were determined.From a profound bias by indication together with a relatively small group on NOM no statistical analysis on differences between groups was performed.Ethical approval for the study was granted by the Institutional Review Board (decision 2016-938). No funding was obtained and the authors have no conflicts of interest to declare. Between 2011 and 2019, 3,467 hip fracture patients were admitted to our hospital of which 1,279 frail elderly hip fracture patients (37%) were admitted to the orthogeriatric ward. From this study group 1,188 patients received surgical treatment whereas for 91 NOM was chosen. As such NOM was offered to 7.1%  of patients admitted to the orthogeriatric ward and to 2.6%  of all patients . As antiIn 18 of 91 patients the decision for NOM was clearly based on patient and family preference whereas medical grounds were not evident. In 49 patients NOM was almost completely dictated on medical grounds (comorbidity and high perioperative risk) and in 24 patients this was a combination of both.The 30-day and 1-year mortality rates in the frail NOM group were 87% and 99%, respectively . Of the The 30-day and 1-year mortality rates in the surgery group were 7% and 28%, respectively . Mean suThis study was primarily conducted to provide more insight into the course of NOM in a selected group of very frail elderly hip fracture patients in whom ACP with patients and relatives had resulted in a shared decision not to operate to prolong life. The 30-day and 1-year mortality rates in this group were 87% and 99%, respectively. In contrast the reference 30-day and 1-year mortality rates in the surgery group were 7% and 28%, respectively. The choice for NOM was at least partly based on patient or family preference in almost half of these patients (46%), whereas the other half was treated nonoperatively mainly based on medical grounds (54%).We found a very high 30-day mortality of 87% in nonoperatively managed hip fracture patients. These findings differ from other previously published studies with a 30-day mortality ranging from 5% to 65%  decision-making. Perhaps more importantly, from the mortality observed in the NOM group it appears that a rapid decline can be expected. Second, the inclusion of patients was limited to those patients admitted to the orthogeriatric ward, also indicating selection bias. However, these frail elderly patients in particular, selected by a comprehensive geriatric assessment, reflect the population of concern in the clinical dilemma of NOM of hip fractures. We feel that this clear selection bias may also reflect the high 30-day and 1-year mortality rates encountered in this study as compared with the available literature.Besides limitations, important strengths also apply. In this study a rather homogeneous group of 91 very frail hip fracture patients were treated nonoperatively. This provided important information on the course of treatment and mortality, which is lacking in the available literature with a smaller number of patients and more importantly inhomogeneous fragility features (van de Ree et al. In conclusion, this study revealed a predictable short survival after NOM of hip fractures in a group of very frail elderly patients where prolonged survival was not considered to be the primary goal of treatment. These results may reassure clinicians, patients, and their relatives that NOM can be regarded as a relevant treatment option with a predictable outcome in very frail hip fracture patients. In the case of limited life expectancy, information regarding nonoperative supportive management and well-managed pain in a palliative setting might help patients and their families to come to a well-founded decision in line with their wishes, goals, and end-of-life expectations. Therefore, in our opinion, NOM should gain more attention and ACP should be part of standardized preoperative hip fracture care in the frailest patients.