Kurt Simons

Laterality of Amblyopia

PURPOSE To determine the frequency of unilateral amblyopia in right versus left eyes among children younger than 18 years. DESIGN Analysis of data collected in randomized clinical trials conducted by the Pediatric Eye Disease Investigator Group. METHODS The laterality of the amblyopic eye was analyzed in 2635 subjects younger than 18 years who participated in 9 multicenter prospective, randomized treatment trials. Eligibility criteria for these clinical trials included unilateral amblyopia associated with strabismus, anisometropia, or both, with visual acuity between 20/40 and 20/400. Logistic regression was used to assess the association of baseline and demographic factors with the laterality of amblyopia. RESULTS Among subjects with anisometropic amblyopia (with or without strabismus), amblyopia was present more often in left than right eyes, with a relative prevalence of 59% in left eyes (95% confidence interval, 57% to 62%; P < .001 from a test of proportion, 50%). However, among subjects with strabismic-only amblyopia, there was no laterality predilection (relative prevalence of 50% in left eyes; 95% confidence interval, 47% to 54%; P = .94). CONCLUSIONS Anisometropic amblyopia, with or without strabismus, occurs more often in left eyes than right eyes. This finding of amblyopia laterality may be related to microtropia, sighting dominance, or other forms of ocular dominance; developmental or neurological factors; laterality in the development of refractive error; or a combination thereof.

Old age and the functional consequences of amblyopia.

Despite the substantial research literature on amblyopia that has accumulated during the last several decades—more than 6,000 publications, according to a PubMed (http://www.ncbi.nlm.nih.gov/sites/ entrez) search—until recently there has been almost no study regarding the central clinical question, how does amblyopia affect function? This gap has begun to be filled. Of particular note is a recent large cohort study (n 8,432 normal and 429 amblyopic subjects) of the effect of amblyopia on an array of functions of everyday life, ranging from education and coordination to injury and occupation. Both questionnaire and performance-based measures were used. The unexpected finding was that unilateral amblyopia had virtually no effect on any of the functions tested. Another large cohort study (n 6,858) with similar tests came to the same conclusion for amblyopia, although it did find significantly poorer motor skill performance in children with manifest strabismus. Other findings conflict with these reports. For instance, amblyopia has been found to significantly reduce speed and dexterity of prehension (particularly in children with a history of strabismus), without diminishing accuracy and control. Evidence also has come to light that amblyopic subjects’ binocular reading speed is significantly slower than that of normal subjects, despite the amblyopic subjects having the same levels of binocular visual acuity and reading acuity as the normal subjects, and also that amblyopic individuals have poorer depth discrimination from motion parallax than normal subjects. However, it seems useful to consider possible reasons for the 2 cohort study findings. Of particular note is the age at which visual function was surveyed. The oldest members of the first cohort study were 49 years of age when the measurements were taken; the oldest members were 7.5 years of age in the second cohort study. There is evidence of an age-related cumulative lifetime risk of binocular visual impairment in at least 1.2% to 3.3% of amblyopic patients. Supporting this age effect is a large study (n 3,654) in which the youngest subjects at pre-