Hemiretinal differences in speed of light detection in esotropic amblyopes.

Nine esotropic amblyopes were tested monocularly in a simple reaction time (RT) paradigm with brief suprathreshold flashes of light presented at various eccentricities along the horizontal meridian of the nasal or temporal hemiretinae. All were clinically amblyopic in one eye only. RT was significantly longer in the amblyopic than in the other eye at 1, 5 and 10 deg but not at 25 and 35 deg from the fovea. Another clearcut finding concerned hemiretinal differences: in the non-amblyopic eye, as in control subjects, RT was faster in the nasal than in the temporal hemiretina and such a difference increased with the eccentricity of stimulus presentation. In the amblyopic eye, however, the only significant hemiretinal effect was at 10 deg with a temporal retina advantage and at 35 deg with a nasal retinal advantage. Furthermore, unlike in normal control subjects and the non-amblyopic eye of our esotropes, in the amblyopic eye there was no increase in RT with the eccentricity of stimulus presentation, except for the most peripheral visual field positions. It can be concluded that esotropic amblyopia affects the speed of suprathreshold light detection in the most central 10 deg of visual field and that the nasal hemiretina is clearly more impaired than the temporal hemiretina.