Strabismus associated with decreased binocular summation

This prospective study found that strabismic patients demonstrate subnormal binocular summation and even binocular inhibition for low contrast acuity, suggesting that strabismus impairs visual function more than previously appreciated.

This may explain why strabismic patients who are not diplopic close one eye in visually demanding situations. This finding clarifies the visual deficits impacting quality of life in strabismic patients and may represent a novel measure by which to evaluate and monitor function in strabismus.

The study’s authors used various psychophysical and electrophysiological tests to evaluate the effect of strabismus on binocular summation in 60 strabismic patients and 80 controls.

Regression analysis revealed a significant worsening of binocular summation with strabismus for 2.5 percent (P  =  0.009) and 1.25 percent (P  = 0 .002) low contrast acuity after accounting for age. For 1.25 percent low contrast acuity, strabismic patients had a mean binocular summation score of less than 1, indicating binocular inhibition (i.e., the binocular score was less than that of the better eye’s monocular score).

There was no significant difference in binocular summation for contrast thresholds on Early Treatment Diabetic Retinopathy Study visual acuity, Pelli-Robson contrast sensitivity, or sweep visual evoked potential contrast sensitivity.