Abstract
PurposeTo measure binocular interaction in amblyopes using a rapid and patient-friendly computer-based method, and to test the feasibility of the assessment in the clinic.MethodsBinocular 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 phase matching 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. The resulting effective contrast ratio of the weak eye was taken as an indicator of interocular imbalance. Testing was performed in an ophthalmology clinic under 8 mins. We examined the relationships between our binocular interaction measure and standard clinical measures indicating abnormal binocularity such as interocular acuity difference and stereoacuity. The test-retest reliability of the testing method was also evaluated.ResultsCompared to normally-sighted controls, amblyopes exhibited significantly reduced effective contrast (∼20%) of the weak eye, suggesting a higher contrast requirement for the amblyopic eye compared to the fellow eye. We found that the effective contrast ratio of the weak eye covaried with standard clincal measures of binocular vision. Our results showed that there was a high correlation between the 1st and 2nd measurements (r = 0.94, p<0.001) but without any significant bias between the two.ConclusionsOur findings demonstrate that abnormal binocular interaction can be reliably captured by measuring the effective contrast ratio of the weak eye and quantitative assessment of binocular interaction is a quick and simple test that can be performed in the clinic. We believe that reliable and timely assessment of deficits in a binocular interaction may improve detection and treatment of amblyopia.
Highlights
Amblyopia is an optically uncorrectable loss of vision, usually in one eye, without any known pathology [1]
The effective contrast ratio (ECR) of the weak eye was estimated by fitting the data with the attenuation model (Eq 4)
The model fits were satisfactory with the mean r2 values of 0.83 for strabismic amblyopia, 0.69 for anisometropic amblyopia, 0.84 for strabismus and 0.88 for normal (Table 2), indicating that about 69 to 88% of variance is accounted for by the model fit
Summary
Amblyopia is an optically uncorrectable loss of vision, usually in one eye, without any known pathology [1]. While it has been long believed that amblyopic vision lacks excitatory binocular connections such as binocular summation [28,29,30] and the existence of remaining binocular interactions mostly involve inhibitory mechanisms [31], the recent findings imply that it is possible to restore normal binocularity by addressing the imbalance in monocular signals These findings, support a beneficial role of assessing interocular imbalance in detecting and treating amblyopia as well as estimating a patient’s prognosis. By addressing inefficiency of psychophysical assessments, such as long testing times and the employment of cumbersome apparatus [19], they improved the clinical utility of such assessment These foregoing studies have successfully demonstrated the efficacy of the rapid and convenient test instrument in assessing binocular interaction in amblyopic individuals and its potential use in the clinic. Whether such assessment can be carried out as a part of routine clinical assessments still remains to be answered
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