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The original online version of this article was revised. The following funding note was added: This work was supported by the New York State Empire Innovator Program, by the National Science Foundation (Award 1734887 to SM-C and SLM; Award 1523614 to SLM), and by the National Institute of Health (Award R01EY031971 to SM-C and SLM; Award R01CA258021 to SM-C and SLM). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Science Foundation nor the National Institutes of Health.

Numerous research studies have demonstrated the scope and value of eye movement recording (EMR). There is now potential for EMR to be helpful in a range of clinical contexts and it could be developed as a routine part of the repertoire of clinical investigations offered by the NHS, at least in tertiary centres. We highlight potential uses and challenges below, as a prelude to further development and debate., Peer Reviewed, Postprint (author's final draft)

Purpose : Infantile nystagmus (IN) is characterised by a continuous, primarily horizontal, involuntary oscillation of the eyes and is often associated with visual impairment. Interventions that reduce the intensity of these oscillations can result in subjective improvements in vision that are not reflected in the conventional clinical measure of visual acuity. A more comprehensive overview of visual function may be provided by the spatiotemporal contrast sensitivity function (stCSF). This study aimed to provide proof of concept for a novel method to measure contrast sensitivity functions (CSFs) at different velocities using the optokinetic response (OKR). Methods : The stCSF was measured in six participants with IN (ages 22-66 years) and six controls (ages 20-30 years). Contrast sensitivity (CS) was estimated by measuring the gain of voluntary OKR to vertically drifting sinusoidal gratings of varying contrast (0.5-100%), velocity (0.5-32°/s), and spatial frequency (0.5-10 cycles/°). The peak CS and its corresponding peak spatial frequency (SF) were found for the CSF at each velocity, and the area under each CSF curve (AUCSF) was calculated. For each metric, a repeated measures analysis of variance (rmANOVA) was performed using velocity as the within-subjects factor and participant group as the between-subject factor. Results : This analysis focused on the CSFs at 4°/s and 8°/s since these velocities obtained the most robust OKR. Peak SF and AUCSF were found to be significantly lower at 8°/s than 4°/s (peak SF: F=6.07, p<0.05; AUCSF: F=30.0, p<0.001), although no significant change was found for peak CS. The CSFs also differed between the two groups, with the IN group showing significantly lower peak CS (F=9.22, p<0.05), peak SF (F=6.07, p<0.05), and AUCSF (F=10.4, p<0.01) than the control group. Conclusions : As velocity increases, CS was found to be progressively reduced and shifted toward lower SFs. These preliminary results also indicate an impairment of CS (i.e.

The onset of a spontaneous oscillation of the eyes can occur at any time in life but is most commonly encountered during childhood. In the UK, nystagmus in the general population has been reported to have a prevalence of 2.4 in 1000. It can occur as an isolated disorder, in association with a number of different eye conditions, or as a result of a range of neurological disorders. The onset of nystagmus in childhood is not rare and can be the cause of significant clinical and parental concern, and sometimes requires urgent investigation. There is currently no standard clinical approach to investigating nystagmus in childhood. This Clinical Practice Point provides a single point of reference for busy clinicians when managing these complex patients from differential diagnosis, through long-term management, to discharge. It also covers provision of support for patients and carers throughout and beyond clinical care pathways. This document is specific to nystagmus in children.

Purpose : Small eye movements (drifts, microsaccades and tremors) keep the eye in continuous motion, even as observers attempt to fixate a target. In this study we examine eye velocity distributions from typical observers as they fixate targets presented at different gaze angle. We hypothesise that the mechanics of the oculomotor plant will bias eye velocity towards primary position. Methods : Twelve typical observers with normal vision were asked to fixate a target (0.4° green dot) presented for 12s at either 0° (primary position) or at eccentricity of ±16° horizontal or ±16° vertical. The targets were presented in a random order against a black background in an otherwise dark room. Observers viewed the targets binocularly and eye movements were recorded at 1000Hz from the eye with better visual acuity. Saccades and blinks were excluded from eye movement data and a bivariate probability density function of target-relative eye velocity was calculated after filtering eye position data. The centroid of the isocontour that encompassed the highest 68% of data was examined to determine any directional bias. Results : Preliminary results show the mean x coordinate of the centroid has a leftward bias (-0.030 ± 0.092°/s) during right-gaze (+16°), and a rightward bias (+0.039 ± 0.120°/s) during left-gaze (-16°). This difference (0.072°/s) was statistically significant [t(11) = 2.697, p = 0.010, d = 0.779]. In contrast, the mean y coordinate of the centroid had a downward bias during up-gaze (-0.217 ± 0.310°/s) and down-gaze (-0.230 ± 0.281°/s). This difference (0.012°/s) was not statistically significant [t(11) = 0.101, p = 0.461, d = 0.029]. There were no significant differences between any of the eccentric gaze positions and primary position (i.e. 0°). Conclusions : We have demonstrated that eye velocity during foveal fixation is dependent on gaze angle. Eye velocity is biased towards primary position during horizontal gaze, and downward during vertical gaze. These finding

Accommodation is vital to produce a clear, focussed image for close work. In nystagmus, a continuous conjugate oscillation of the eyes, studies on accommodation are lacking. Ong et al. (1993) demonstrated normal static accommodation, apart from increased depth of focus, in nystagmats. However, in determining the dynamics of accommodation in people with nystagmus, it is unknown how accurate refractive findings will be off-axis. We therefore sought to discover the effect of off-axis positions on measured refractive error during convergence. In six presbyopes without nystagmus (age: 43–70), we used the PowerRef 3 (PlusoptiX R09), which provides continual recording of refractive error, to quantify the effect of imposing different values of defocus (+4, +3, +2, +1, −2 and −4 D) off-axis and centrally. At 1 m, measurements were obtained when participants fixated the PowerRef 3 and at four gaze positions spaced c.2° apart, on either side of the instrument. For positions to the left, readings were obtained for the right eye and vice versa. The lens-induced refractive changes did not differ from the expected change both at the centre and off-gaze positions (except for a −2 D lens at 4°; p = .037). However, these values were all significantly correlated. For gaze position up to 8°, refraction measured was not significantly different from that at the central position (F value range: 0.048–0.778; p value range: 0.624–1.000). Therefore, off- axis refraction measured using the PowerRef 3 remains reliable up to 8°, implying that we will be able to record the stability of refraction during nystagmus eye movement.

Infantile nystagmus (IN) is a pathological condition of continuous, horizontal eye oscillations. Despite ongoing eye movements, those with IN do not experience oscillopsia, i.e. the illusory perception that the environment is moving to-and fro. The correct use of neural compensation for their eye movements, just as in typical individuals, is hypothesised to account for this lack of oscillopsia. This neural mechanism requires that an estimate of eye velocity (‘extra-retinal signal’) be compared to an estimate of the motion of the retinal image (‘retinal signal’), and any difference due to object motion. Despite this hypothesis, there have been no previous investigations on how accurately those with IN can estimate object motion. Even in typical adults, eye movement compensation is not perfect, which underlies a number of pursuit-based illusions. One such illusion, the Filehne illusion can be used to investigate the relative mismatch between the extra-retinal and retinal signals as individuals judge their perception of stationarity while attempting to follow a moving target. This illusion was used to investigate, through comparison with typical individuals, whether those with IN correctly recover object motion. Experiments were conducted to characterise the ability of those with IN to fixate as well as follow targets, using a novel two-dimensional eye movement measure. Under repeated testing, the fixation gaze angle at which the IN oscillation is minimum (a null zone) was not consistent. Moreover, those with IN were unable to accurately or precisely follow targets using their slow phase. Results from a comparison of fixation and pursuit performance in those with IN suggested no difference in either the accuracy or precision. Importantly, the psychophysical judgements of those with IN pursuit eye movements are prone to similar compensation errors as typical controls. However, the mechanisms by which this is achieved will require further exploration.

Infantile nystagmus (IN) is a pathological condition of continuous, horizontal eye oscillations. Despite ongoing eye movements, those with IN do not experience oscillopsia, i.e. the illusory perception that the environment is moving to-and fro. The correct use of neural compensation for their eye movements, just as in typical individuals, is hypothesised to account for this lack of oscillopsia. This neural mechanism requires that an estimate of eye velocity (‘extra-retinal signal’) be compared to an estimate of the motion of the retinal image (‘retinal signal’), and any difference due to object motion. Despite this hypothesis, there have been no previous investigations on how accurately those with IN can estimate object motion. Even in typical adults, eye movement compensation is not perfect, which underlies a number of pursuit-based illusions. One such illusion, the Filehne illusion can be used to investigate the relative mismatch between the extra-retinal and retinal signals as individuals judge their perception of stationarity while attempting to follow a moving target. This illusion was used to investigate, through comparison with typical individuals, whether those with IN correctly recover object motion. Experiments were conducted to characterise the ability of those with IN to fixate as well as follow targets, using a novel two-dimensional eye movement measure. Under repeated testing, the fixation gaze angle at which the IN oscillation is minimum (a null zone) was not consistent. Moreover, those with IN were unable to accurately or precisely follow targets using their slow phase. Results from a comparison of fixation and pursuit performance in those with IN suggested no difference in either the accuracy or precision. Importantly, the psychophysical judgements of those with IN pursuit eye movements are prone to similar compensation errors as typical controls. However, the mechanisms by which this is achieved will require further exploration.