[Binocularity after treatment for constant exotropia]

We studied the binocularity of cured chronic exotropic patients and discussed the critical period of gross stereopsis and its vulnerability. An infant, developing chronic exotropia associated with myasthenia gravis at the age of 17 months, returned to exophoria 10 months later and showed a stereo-acuity of 800 sec. This clinical finding suggests that the critical period for gross stereopsis is before the age of 18 months and the function is recoverable even when it is suppressed for several months after that period. Of the 18 patients with chronic exotropia who had undergone surgery after school age. 16 patients (83.3%) recovered stereoacuity of 3,000 sec or better, which suggests that gross stereopsis once established will never vanish. Patients with chronic exotropia with poor central vision also recovered gross stereopsis and stable eye position after strabismus surgery, indicating that gross stereopsis with peripheral fusion is significant for the stabilization of the eye position.