Why does early surgical alignment improve stereoacuity outcomes in infantile esotropia?

Purpose: Recent studies of infantile esotropia suggest that early surgical alignment may enhance stereopsis and that alignment during the first 6 mont hs of life may be optimal. Early surgery both establishes alignment during an early critical period for the development of stereopsis and minimizes th e duration of misalignment. Here we examine the role of these 2 factors in promoting improved stereopsis outcomes. Methods: Participants were 129 cons ecutive patients enrolled in a prospective study of infantile esotropia who were followed up for a minimum of 5 years. At ages 5 to 9 years, Randot st ereopsis was evaluated. Results: Multiple linear regression indicated that duration of misalignment, but not age at alignment or age at onset, was a s ignificant factor in determining random dot stereopsis outcomes. Moreover, patients with stereopsis were less likely to have a loss of horizontal eye alignment requiring surgery than patients without stereopsis (14% versus 32 %; z = 1.96, P = .05). Patients with stereopsis were also less likely to ha ve dissociated vertical deviation than patients without stereopsis (25% ver sus 63%; z = 3.36, P < .001). Conclusions: The results suggest that early s urgical alignment is associated with better stereopsis in those patients wi th infantile esotropia who were treated during the first 24 months of life, because early surgery minimizes the duration of misalignment, not because alignment is achieved during an early critical period of visual maturation. Random dot stereopsis can also be achieved in patients with alignment prov ided that the duration of misalignment is not prolonged. Improved outcomes of random dot stereopsis are associated with more stable longterm alignment outcomes.