Abstract
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., CSF depressed and shifted leftward) in IN compared to controls that may be a consequence of their eye movements. Our method, relying on the reflexive OKR, could be used to measure the stCSF in babies as well as adults with IN to better assess the efficacy of therapeutic interventions for IN. Ongoing work includes data collection from larger, age-matched cohorts.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.