Effect of Rapid Alternating and in phase flicker occlusion on Stereopsis

Abstract

Purpose : Rapid alternating occlusion of the eyes is a relatively new treatment for amblyopia that has shown promise for improving both stereoacuity and visual acuity in some amblyopic subjects. Previously we looked at the effect of alternate and in-phase occlusion on vergence eye movements and found that vergence responses were disrupted by out-of-phase flicker more than in-phase flicker, particularly at lower frequencies. In this current study compared the effect of alternate vs. in phase occlusion of different frequency on stereopsis for normal subjects, to dissociate the effect of flicker per se from the effect of alternate occlusion.

Methods : Disparity thresholds were measured using a 30 trial, 1 up 2 down staircase beginning at 10 arc minutes disparity. Five staircases were obtained from five healthy adult subjects for all combinations of contrast (100%, 50%, 25%) and flicker (2, 4, 8, 16 and 32 Hz, In-phase and out of phase binocular flicker, and no flicker). The stimulus was a filtered noise pattern (1 cpd, 1 octave bandwidth), presented for one second. Horizontal disparity was added to one half of the image, and subjects indicated which half appeared closer. Left and right eye images were displayed side by side on a gamma corrected monitor and viewed through a mirror haploscope while wearing Eyetronix shutter glasses. With shutter glasses open the luminance was 71cd/m^{2 ,} closed it was 0.53cd/m². Testing distance was 97cm.

Results : Flicker elevated stereoscopic thresholds in most subjects. The flicker did not abolish stereopsis, however: subjects were able to detect a few arc minutes of disparity at all but the lowest frequencies of out-of-phase flicker. Two subjects showed almost no effect of flicker on stereo thresholds except at the lowest frequencies of out-of-phase flicker.

Conclusions : The results of this study show that stereopsis thresholds are elevated by both alternate and in phase flicker but are severely impacted only at the lowest temporal frequencies of 2 and 4 Hz. Flicker overall had an impact on three of five subjects. Taken together with our findings on vergence, it appears that the alternating occlusion provides some of the effects of patching, while still allowing binocular function during treatment, but the dramatic flickering may be disruptive for many subjects.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.