Relationship between anisometropia, amblyopia, and binocularity.

PURPOSE: To determine if higher degrees of anisometropia cause deeper amblyopia and poorer binocularity than lower degrees of anisometropia in children and adults.
METHODS: The clinical records for 60 patients with untreated anisometropic amblyopia without strabismus, ranging in age from 3 to 39 years, were reviewed. The refractive error, the initial best corrected visual acuities in the amblyopic and nonamblyopic eyes, and the level of binocularity were recorded from each chart. The degree of anisometropia was determined by: (1) calculating the difference between spherical equivalents for each eye; (2) calculating the difference in the vertical meridians for each eye; (3) calculating the difference in the horizontal meridians for each eye; and (4) calculating the root mean square difference which also takes into account differences in astigmatic axis. The depth of amblyopia was determined by converting the visual acuity score to its logarithmic value, logarithm of the minimum angle of resolution (logMAR), and calculating the difference between the amblyopic and nonamblyopic eye. The level of binocularity was determined from stereopsis testing.
RESULTS: For all patients, there was a significant relationship between the four measures of anisometropia, the depth of amblyopia, and the level of binocularity (median correlations 0.61 and 0.61, respectively). For the myopes (N = 10), there was no significant relationship between the 4 measures of anisometropia, the depth of amblyopia, and the level of binocularity (median correlations 0.34 and 0.61, respectively). For the hyperopes (N = 50), the relationship was significant for all 4 measures of anisometropia (median correlations 0.72 and 0.62, respectively).
CONCLUSION: As the degree of anisometropia increases, the depth of amblyopia becomes greater and the level of binocularity becomes poorer, at least for hyperopic patients.