Abstract
Purpose :
Alternate occlusion therapy has been reported to improve stereoacuity and visual acuity in some amblyopic subjects. We wondered how alternate occlusion flicker affects binocular function during the therapy. Here we tested the effects of alternate occlusion flicker on symmetrical vergence responses to disparity steps.
Methods :
Vergence eye movements were measured using a dual Purkinje image eye tracker. The stimulus used for the testing was a filtered noise pattern of spatial frequency 0.25 or 2 c/deg with a bandwith of 1 octave and variable contrast. Trials were 2 seconds long, with a near or far disparity step at either 250 or 350 msec into the trial. Data were collected in blocks of 120 trials (6 contrast x 5 flickers x 2 directions x 2 onset times) in shuffled order. Ten blocks were collected at 2 c/deg and 4 at .25 c/deg.
Results :
Vergence latency was measured as the time taken by the subject to reach half of the total vergence demand (1 deg). At the lowest flicker rates tested, 2 and 4 Hz, vergence responses were absent or very slow. At 8 hertz flicker, vergence was present but delayed for all contrast levels. At the highest flicker rates, 16 and 32 Hz, responses were robust and rapid for all but the lowest contrasts.
Conclusions :
Alternate occlusion flicker at 2 and 4 Hz abolished responses to disparity steps in our stimuli. Flicker at 8 Hz, similar to that used previously for therapy, delayed and disrupted vergence in our normal subjects but did not abolish it.
This is a 2020 ARVO Annual Meeting abstract.