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Purpose: This study presents test-retest reliability of optotype visual acuity (OVA) across 60° of horizontal gaze position in patients with infantile nystagmus syndrome (INS). Also, the validity of the metric gaze-dependent functional vision space (GDFVS) is shown in patients with INS., Methods: In experiment 1, OVA was measured twice in seven horizontal gaze positions from 30° left to right in 10° steps in 20 subjects with INS and 14 without INS. Test-retest reliability was assessed using intraclass correlation coefficient (ICC) in each gaze. OVA area under the curve (AUC) was calculated with horizontal eye position on the x-axis, and logMAR visual acuity on the y-axis and then converted to GDFVS. In experiment 2, validity of GDFVS was determined over 40° horizontal gaze by applying the 95% limits of agreement from experiment 1 to pre- and post-treatment GDFVS values from 85 patients with INS., Results: In experiment 1, test-retest reliability for OVA was high (ICC ≥ 0.88) as the difference in test-retest was on average less than 0.1 logMAR in each gaze position. In experiment 2, as a group, INS subjects had a significant increase (P < 0.001) in the size of their GDFVS that exceeded the 95% limits of agreement found during test-retest., Conclusions: OVA is a reliable measure in INS patients across 60° of horizontal gaze position. GDFVS is a valid clinical method to be used to quantify OVA as a function of eye position in INS patients. This method captures the dynamic nature of OVA in INS patients and may be a valuable measure to quantify visual function patients with INS, particularly in quantifying change as part of clinical studies.

Purpose: Nystagmus eye movement data from infants and young children are often not suitable for advanced quantitative analysis. A method was developed to capture useful information from noisy data and validate the technique by showing meaningful relationships with visual functioning., Methods: Horizontal eye movements from patients (age 5 months-8 years) with idiopathic infantile nystagmus syndrome (INS) were used to develop a quantitative outcome measure that allowed for head and body movement during the recording. The validity of this outcome was assessed by evaluating its relation to visual acuity deficit in 130 subjects, its relation to actual fixation as assessed under simultaneous fundus imaging, its correlation with the established expanded nystagmus acuity function (NAFX), and its test-retest variability., Results: The nystagmus optimal fixation function (NOFF) was defined as the logit transform of the fraction of data points meeting position and velocity criteria within a moving window. A decreasing exponential relationship was found between visual acuity deficit and the NOFF, yielding a 0.75 logMAR deficit for the poorest NOFF and diminishing deficits with improving foveation. As much as 96% of the points identified as foveation events fell within 0.25° of the actual target. Good correlation (r = 0.96) was found between NOFF and NAFX. Test-retest variability was 0.49 logit units., Conclusions: The NOFF is a feasible method to quantify noisy nystagmus eye movement data. Its validation makes it a promising outcome measure for the progression and treatment of nystagmus during early childhood.

Purpose: Infantile nystagmus syndrome (INS) can be idiopathic or associated with ocular or systemic disease. The ocular oscillation of INS directly contributes to loss of visual acuity. In this study, visual acuity development in patients with INS was examined., Methods: Children with INS were classified as having idiopathic INS (n = 84) or INS with an associated sensory deficit: INS and albinism (n = 71), bilateral optic nerve hypoplasia (ONH; n = 23), or congenital retinal disorder (n = 36). Visual acuity was assessed with Teller cards and/or optotypes, and the data were analyzed for three age groups (<24 months, 24-48 months, and >48 months)., Results: Patients with idiopathic INS showed mildly reduced visual acuity early in life and gradual maturation with age that paralleled a normative curve. Patients with albinism also showed a mild visual deficit early in life but failed to keep pace with the normative curve, showing a gradual increase in visual acuity deficit. Patients with ONH and congenital retinal disorders exhibited more severe visual acuity deficits during infancy. The ONH group displayed slow improvement of visual acuity with a plateau at 24 months through >48 months, with a small increase in visual acuity deficit. The congenital retinal disorder group had no significant change in visual acuity across age and had a rapid increase in visual acuity deficit., Conclusions: The pattern of visual acuity development differs among children with INS, depending on the presence or absence of associated sensory system deficits. Careful characterization of visual system differences in patients with INS is important if visual acuity is an outcome in clinical trials.

Purpose: To perform ocular motility recordings of infantile nystagmus (IN) in RPE65-deficient canines and determine whether they can be used as a motor indicator of restored retinal function to investigate the effects of gene therapy., Methods: Treated and untreated canines were comfortably suspended in a custom-built sling and encouraged to fixate on distant targets at gaze angles varying between +/-15 degrees horizontally and +/-10 degrees vertically. Ocular motility recordings were made, using two distinct methods-infrared reflection and high-speed video. The resultant recordings from three untreated, four treated, and three pre- and post-treatment dogs were analyzed for using the eXpanded Nystagmus Acuity Function (NAFX), which yields an objective assessment of best potential visual acuity, based on the duration and repeatable accuracy of foveation and centralisation., Results: During fixation, the untreated dogs exhibited large-amplitude, classic IN waveforms, including pendular and jerk in both the horizontal and vertical planes, which prevented them from keeping the targets within the area centralis (the region of highest receptor density, spanning +/-3 degrees horizontally by +/-1.5 degrees vertically, analogous to the fovea). Some untreated dogs also had small-amplitude (0.5-1 degrees), high-frequency (6-9 Hz) oscillations. Under the same conditions, successfully treated canines no longer exhibited clinically detectable IN. Their IN was converted to waveforms with very low amplitudes that yielded higher NAFX values and allowed target images to remain well within the area centralis. Of note, uniocular treatment appeared to damp the IN in both eyes. Behaviorally, the treated dogs were able to successfully navigate through obstacles more easily without inadvertent contact, a task beyond the untreated dogs' ability., Conclusions: Gene therapy that successfully restored retinal function also reduced the accompanying IN to such a great extent that it was not clinically detectable approximately 90% of the time in many of the dogs. IN improvement, as quantified by the NAFX, is an objective motor indicator of visual improvement due to gene therapy.