Preferential-looking acuity and stereopsis in infantile esotropia.

One hundred esotropic infants were assessed by preferential-looking (PL) for monocular acuity and stereopsis before the initiation of treatment. PL acuity of infantile esotropes who freely alternated fixation and of preferred eyes of unilateral esotropes was not significantly different from monocular acuity of age-matched normal infants. PL acuity of non-preferred eyes was normal during months three to five, but frequently below normal during months six to 14. Approximately the same percentage of normal and esotropic infants aged three to four months demonstrated stereopsis, but fewer esotropes than normals demonstrated stereopsis, during months five to 14. Ninety-five percent of infants judged non-amblyopic by the cover-uncover test also showed no evidence of amblyopia in the PL test. Overall, 42% of esotropic infants judged amblyopic by the cover-uncover test were found amblyopic by PL. Most discrepancies between PL and fixation preference (73%) occurred when clinically amblyopic infants under eight months of age were found non-amblyopic by PL. These findings suggest that fixation preference develops prior to the onset of amblyopia detectable by PL. The results of PL stereopsis testing suggest that stereoscopic pathways are present and potentially functional in at least some esotropic infants.