Visual processing in infantile nystagmus is not slow

Purpose: Treatments for infantile nystagmus (IN) sometimes elicit subjective reports of improved visual function, yet quantifiable improvements in visual acuity, if any, are often negligible. One possibility is that these subjective “improvements” may relate to temporal, rather than spatial, visual function. This study aimed to ascertain the extent to which “time to see” might be increased in nystagmats, as compared to normally sighted controls. By assessing both eye movement and response time data, it was possible to determine whether delays in “time to see” were due solely to the eye movements, or to an underlying deficit in visual processing. Methods: The time taken to respond to the orientation of centrally and peripherally presented gratings was measured in subjects with IN and normally sighted controls (both groups: n = 11). For each vertically displaced grating, the time until the target-acquiring saccade was determined, as was the time from the saccade until the subject's response. Results: Nystagmats took approximately 60 ms longer than controls to execute target-acquiring saccades to vertically displaced targets (P = 0.010). However, the time from the end of the saccade until subjects responded was not significantly different between groups (P = 0.37). Despite this, nystagmats took longer to respond to gratings presented at fixation. Conclusions: Individuals with IN took longer to direct their gaze toward objects of interest. However, once a target was foveated, the time taken to process visual information and respond did not appear to differ from that of control subjects. Therefore, conscious visual processing in IN is not slow