Preservation of position and motion stereopsis in strabismic subjects.

Preservation of position (PS) and motion stereopsis (MS) of strabismic subjects in central and peripheral visual fields (N = 51) was studied in relationship with various strabismic parameters and aspects: present and past squint angles, age at the time of strabismic appearance and the first treatment, present visual acuities, and present and past strabismic polarity (convergent or divergent). The present squint angle was the only major parameter relevant for the preservation of PS and MS. The critical squint angle for the preservation was virtually null for central MS (it was present in 12 of the 16 subjects with squint angles smaller than the critical value), 2 degrees for central PS (17/18), 5 degrees for peripheral PS (23/28), and 10 degrees for peripheral MS (37/42). These findings indicate the importance of correction of visual axes in the preservation of stereopsis. The finding that the central and peripheral types of PS and MS could occur independently in strabismic subjects also suggests that they are based on different neural mechanisms.