Greater eye movement disconjugacy with near fixation in amblyopia during binocular viewing is associated with increased microsaccade rate

Abstract

Purpose : To determine whether increased eye movement disconjugacy with near fixation in amblyopic subjects during binocular viewing is associated with changes in microsaccade parameters.

Methods : Binocular eye movements were recorded at 500 Hz using the EyeLink 1000 eye tracker (SR Research Ltd., Ontario, Canada). Eleven amblyopic subjects, age 8-45 years, were asked to fixate on a blue cross subtending 0.5° at a near distance of 57 cm or at a far distance of 4 m for 20-second epochs of binocular or monocular viewing. Microsaccade number, duration, peak velocity, direction, binocularity, and reversals of direction (square-wave jerk configuration) were recorded. Means and standard deviations were calculated, and significance testing was performed with the Student’s t-test.

Results : Amblyopic subjects during binocular viewing showed more microsaccades with near fixation (1.4±0.1 microsaccades/s) than with far fixation and (1.9±0.2 microsaccades/s; P=0.02) and fewer reversals in direction with near fixation than with far fixation (49±22 % near vs. 58±16 % far; P=0.01). Both viewing conditions showed similar microsaccade duration (95±200 ms vs. 66±83 ms) and peak velocity (42±28 deg/s vs. 37±18.5 deg/s).

Conclusions : Increased disconjugacy with near fixational eye movements for amblyopic subjects during binocular viewing is associated with an increase in the number of microsaccades in the same direction. This increase in microsaccade rate with near fixation may indicate subclinical manifest latent nystagmus possibly from increased suppression of the amblyopic eye during accommodation to the near target.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.