Purpose: To measure binocular interaction in amblyopes using a rapid and patient-friendly computer-based method, and to estimate the clinical value of this additional information for detecting and monitoring changes in amblyopic vision.
Methods: Binocular interaction was assessed in subjects with strabismic amblyopia (n=7), anisometropic amblyopia (n=6), strabismus without amblyopia (n=15) and normal vision (n=40). Binocular interaction was measured with a dichoptic task in which subjects matched the position of a binocular probe to the cyclopean perceived phase of a dichoptic pair of gratings whose contrast ratios were systematically varied. Testing was performed in an ophthalmology clinic in under 8 mins. We assessed the relationship between binocular interaction, interocular acuity difference and stereoacuity, which are standard clinical measures of binocular visual function. Logistic regression and principal components analyses were used to determine the contribution of binocular interaction in identifying amblyopia.
Results: Compared to normally-sighted controls, amblyopes exhibited significantly reduced effective contrast (~20%) of the weak eye suggesting a higher contrast requirement for the amblyopic compared to the strong eye. The effective contrast ratio of binocular vision was closely related to standard clincal measures of binocular vision. Furthermore, knowing the effective contrast of the weak eye contributed significantly to classifying patients as amblyopic vs. non-amblyopic.
Conclusions: Our findings demonstrate that abnormal binocular interaction can be reliably captured by measuring the effective contrast of the weak eye and quantitative assessment of binocular interaction is a quick and simple test that can be performed in the clinic. This suggests that reliable and timely assessment of deficits in a binocular interaction measure may improve detection of amblyopia and allow clinicians to more accurately assess individual patients’ outcomes and prognosis in addition to standard visual acuity.