Saccadic and Manual Reaction Times in Amblyopia

Abstract:

It has been known for over half a century that both saccadic and manual reaction times are longer for stimuli presented to the amblyopic eye than to the fellow eye, or to normal eyes.   From the extensive literature on this topic, there are two consistent findings.  First, the worse the acuity in the amblyopic eye the longer the manual and saccadic reaction times.  Second, strabismic amblyopes are generally slower to respond to stimuli presented to their amblyopic eyes than are anisometropic amblyopes.  Christina Gambacorta’s research, performed here at Smith-Kettlewell, showed: 1) when the contrast was equated in the two eyes of her anisometropic amblyopic subjects, there were no differences in their reaction times;  2) the long reaction times in the amblyopic eyes of some of her strabismic subjects were not due to reduced contrast sensitivity; 3) saccadic and manual reaction times to identical targets are highly correlated in amblyopic eyes, but the interocular difference in manual reaction time is about half the difference in saccadic reaction time.  Gambacorta, Ding, McKee, and Levi (2018) speculated that these findings can be explained by the many microsaccades made while some strabismic observers attempt to stabilize their amblyopic eyes against drift.  I will present our results and the reasoning supporting this speculation.