Are Covert Saccade Functionally Relevant in Vestibular Hypofunction?
The vestibulo-ocular reflex maintains gaze stabilization during angular or linear head accelerations, allowing adequate dynamic visual acuity. In case of bilateral vestibular hypofunction, patients use saccades to compensate for the reduced vestibulo-ocular reflex function, with covert saccades occurring even during the head displacement. In this study, we questioned whether covert saccades help maintain dynamic visual acuity, and evaluated which characteristic of these saccades are the most relevant to improve visual function. We prospectively included 18 patients with chronic bilateral vestibular hypofunction. Subjects underwent evaluation of dynamic visual acuity in the horizontal plane as well as video recording of their head and eye positions during horizontal head impulse tests in both directions (36 ears tested). Frequency, latency, consistency of covert saccade initiation, and gain of covert saccades as well as residual vestibulo-ocular reflex gain were calculated. We found no correlation between residual vestibulo-ocular reflex gain and dynamic visual acuity. Dynamic visual acuity performance was however positively correlated with the frequency and gain of covert saccades and negatively correlated with covert saccade latency. There was no correlation between consistency of covert saccade initiation and dynamic visual acuity. Even though gaze stabilization in space during covert saccades might be of very short duration, these refixation saccades seem to improve vision in patients with bilateral vestibular hypofunction during angular head impulses. These findings emphasize the need for specific rehabilitation technics that favor the triggering of covert saccades. The physiological origin of covert saccades is discussed.
['Hermann|R|R|', 'Pelisson|D|D|', 'Dumas|O|O|', 'Urquizar|Ch|C|', 'Truy|E|E|', 'Tilikete|C|C|http://orcid.org/0000-0002-1452-1398']
D000328:Adult D000368:Aged D000369:Aged, 80 and over D053483:Eye Movement Measurements D005260:Female D064087:Head Impulse Test D006801:Humans D008297:Male D008875:Middle Aged D011446:Prospective Studies D012027:Reflex, Vestibulo-Ocular D012438:Saccades D015837:Vestibular Diseases D014792:Visual Acuity D055815:Young Adult
Dynamic visual acuity Head impulse test Bilateral vestibulopathy Eye movement record Oscillopsia Vestibular areflexia