The effects of unilateral deprivation amblyopia on fixation stability

Deprivation amblyopia is a neurodevelopmental disorder caused by obstruction of the visual pathway due to congenital cataracts, ptosis or corneal opacities that occur during early visual development. Visual deficits persist into adulthood even though the obstruction (e.g. cataracts) have been removed early in life. The effects of deprivation amblyopia on oculomotor control have not been studied. The present study evaluates the effects of unilateral deprivation amblyopia resulting from congenital cataracts on fixation stability.

Seven adults with unilateral deprivation amblyopia and 18 adults with normal vision were tested during binocular and monocular viewing. A video-based eye tracker was used to record eye position of the viewing eye(s) (closed-loop condition with visual feedback) and the covered eye (open-loop condition with no visual feedback).

Findings for the control group were consistent with previous studies. Fixation stability (eye position stability), evaluated using bivariate contour ellipse area (BCEA), microsaccade rate, amplitude and slow drift velocity, was best during binocular viewing, and significantly worse during open-loop monocular viewing. In comparison to the control group, patients had similar fellow eye fixation stability under binocular viewing, but fixation (eye position stability) was poorer under monocular closed-loop and open-loop viewing. Fixation stability was worst in the amblyopic eye in all viewing conditions.

Our findings demonstrate fixation stability deficits in adults with unilateral deprivation amblyopia, underscoring the lasting impact of early visual deprivation on oculomotor function.