Abstract
Purpose: :
The extent to which individuals with amblyopia are visually disadvantaged has generated renewed research interest. Here we investigate (i) whether amblyopes with both eyes open perform differently to visual normals in a simple detection task, and (ii) the contribution of the amblyopic eye under habitual viewing conditions.
Methods: :
For 10 visual normals and 15 amblyopes, blue-on-yellow sensitivity was determined along the horizontal meridian to an eccentricity of 25 degrees either side of a fixation mark. Three viewing conditions were used: 1) both eyes open ie habitual viewing, 2) yellow filter before the amblyopic eye and 3) yellow filter before the fellow eye. The blue stimulus was invisible through the yellow filter and this enabled the sensitivity of each eye to be determined when the eyes are minimally dissociated and in their habitual motor position. Data were analysed using a simple linear regression model repeated for each individual to characterise the contributions of each eye to habitual sensitivity (STATA 9.2)
Results: :
(i) There was no significant difference in sensitivity in habitual viewing between amblyopes and visual normals (p=0.98). (ii) The extent to which the amblyopic eye contributed to habitual viewing peformance varied considerably between amblyopes. Only 20% of amblyopes showed habitual performance that was principally governed by the sensitivity of the fellow eye. In 47% of the sample the amblyopic eye contributed via summation to (n=5), or governed (n=2), habitual performance across a substantial region of the horizontal meridian. For the remaining 33% monocular sensitivities matched habitual sensitivity over many tested locations.
Conclusions: :
Relative to visual normals, amblyopes are not disadvantaged on this task. Our results suggest that the amblyopic eye may make a useful contribution to habitual visual performance in the binocular field in up to eighty percent of amblyopes.