Strabismus affects 2% to 4% of the infant population, with infantile esotropia being the most common form in Western populations.1, 2 Investigations of strabismus found in the literature are primarily oriented toward describing different forms of strabismus and evaluating outcomes of surgical intervention. However, there are a small number of research groups that have tried to improve our basic understanding of strabismus mechanisms by performing studies in nonhuman primates. In this issue of the Journal, one of the leading groups, led by Dr. Larry Tychsen of Washington University in St. Louis, describes their studies examining properties of naturally occurring esotropia in macaque monkeys.3 They have used a comprehensive approach in their investigation by examining eye alignment and eye movement behavior in the strabismic monkeys followed by the use of anatomical methods to analyze binocularity in primary visual cortex (area V1) and the use of anatomical and magnetic resonance imaging methods to analyze extraocular muscles. They make several important points
