Natural History of Monofixation and Amblyopia in Infantile Esotropia during the First 18 Months of Life

Abstract

Abstract: : Purpose: It is difficult to examine the relationship between monofixation (absence of foveal fusion) and amblyopia in older children with infantile esotropia because almost all exhibit monofixation and have a history of amblyopia. The present study examines the relationship between monofixation and amblyopia during the first 18 months of life. Methods: Thirty-four infants aged 2-18 months with infantile esotropia diagnosed before 6 months of age participated. Monofixation was evaluated by means of the nasal-temporal asymmetry in the motion visual evoked potential to quadrature motion. Patients with significant F1 responses and 180 deg interocular phase difference were considered to have monofixation. Amblyopia was assessed by fixation preference on the cover-uncover test. Results: About half of the infants under the age of 6 months (56%) were amblyopic. At this early stage of the disease, monofixation was prevalent among amblyopes (50%) but few (13%) nonamblyopic infants had monofixation. The prevalence of monofixation in amblyopic infant remained fairly constant with increasing age (62% at 6-12 months) and following surgical alignment (57% at 6-12 months and 59% at 12-18 months). By comparison, dramatic changes in the prevalence of monfixation were observed for nonamblyopic infants as a function of age (4-fold increase to 50% at 6-12 months; p=0.11) and surgical alignment (5-fold increase to 70% at 6-12 months and 78% at 12-18 months; p=0.03). Conclusion: Amblyopia may be more prevalent in early infantile esotropia than is commonly believed and infantile amblyopia is associated with a much higher prevalence of monofixation. The finding that few nonamblyopic infants exhibit monofixation early in the course of infantile esotropia suggests they may initially have the capacity for foveal fusion. Thus, monofixation does not appear to represent the persistence of immaturity but rather a pathologic disruption of binocularity. The large increases in prevalence of monofixation in non-amblyopic infants with age and surgery suggests that duration of esotropia and surgical alignment may contribute to the development of foveal suppression in infantile esotropia.

Keywords: 313 amblyopia • 400 esotropia and exotropia • 622 visual development