Static accommodation in congenital nystagmus.

PURPOSE To conduct a comparative study of static accommodative function between individuals with normal vision (n = 10) and patients with congenital nystagmus (n = 12). METHODS The component contribution to monocular steady-state accommodation (slope of the accommodative stimulus/response function, accommodative controller gain, tonic accommodation, and depth-of-focus) was assessed subjectively using a Hartinger coincidence-optometer, except for depth-of-focus, which was determined psychophysically. RESULTS The group mean slope for the patients with nystagmus was not significantly different from that found in the normal subjects. However, their variability was markedly increased. Therefore, the patients with nystagmus were divided into three subgroups with regard to the normal accommodative stimulus/response function slope criterion. The majority of patients with nystagmus (n = 10) exhibited slopes that were outside of normal limits, being greater than (n = 4) or less than (n = 6) the normal range. Depth-of-focus was the only parameter found to be significantly different between the normal and the nystagmus groups. When the nystagmus group was divided with respect to etiology--ie, albinotic (n = 4) versus idiopathic (n = 8)--there were no significant differences found for the various accommodative parameters. CONCLUSIONS We speculate that the primary component contributing to the anomalous accommodative behavior was the increased depth-of-focus, with this perhaps being related to abnormal fixational eye movements and eccentric fixation, and more generally related to overall reduced sensitivity resulting from the early abnormal visual experience.