Gap effect and express saccades generation in amblyopia

Amblyopia is a neurodevelopmental vision disorder that is associated with abnormal visual stimulation during early childhood. Although our knowledge regarding spatial vision deficits in amblyopic subjects is well established, the neural control of eye movements in amblyopia is yet to be explored. In the present study we have evaluated the gap effect, and for the first time (to our best knowledge), express saccades generation in amblyopic (strabismic as well as anisometropic) and age-matched control subjects. We have compared the saccadic latency under different gap conditions ("no gap," 50 ms gap, and 200 ms gap), between the amblyopic and control groups. Our results have shown that saccadic latency was reduced during the gap paradigms both for amblyopic and control groups for all viewing conditions. Furthermore, the size of the gap effect was comparable for all groups and viewing conditions (both for short and long gap durations). In addition, consistent with previous results, the amblyopic eye has manifested an increased saccadic latency as compared to the nondominant eye in the control group. Regarding the occurrence of express saccades, the 200 ms gap condition was associated with an increased number of express saccades as compared to 50 ms gap and "no gap" conditions, both for amblyopic and control subjects. We did not observe any significant difference in terms of express saccades production between the control and amblyopic subjects. Our findings may suggest that amblyopia does not alter physiological mechanisms related to the efficiency of visual attention/fixation disengagement as supported by the observation that the gap effect and express saccades production was comparable between the normal and amblyopic subjects.