Effect of Occlusion Therapy on Visual Acuity, Contrast Sensitivity and Stereopsis in Amblyopia

To determine the effect of occluding a normal eye on visual acuity, contrast sensitivity and stereopsis in amblyopic school children. Amblyopic children from primary schools of region 2 in Mashhad were identified and referred to Optometry Clinics of Mashhad Medical University through a screening program. Informed consent was obtained from the parents. All subjects underwent an ophthalmologic examination including visual acuity, subjective refractive error, biomicroscopy and funduscopy. Best-corrected visual acuity (BCVA), contrast sensitivity and stereopsis were measured by Snellen E chart, Cambridge low contrast chart and Titmus stereotest, respectively. All tests were repeated 2 weeks, 1 month and 3 months after initial examination. Of 1,947 children, 289 (14.8%) were amblyopic of whom 62 subjects were eventually enrolled for the study. BCVA in the amblyopic eye was less than 3/10 in 25.8% of subjects before treatment however all children had BCVA of 3/10 or better afterwards. Mean BCVA in amblyopic eyes significantly increased from 0.53±0.26 logMAR to 0.24±0.23 logMAR after 2 months of treatment (P<0.001). Mean contrast sensitivity in amblyopic eyes was 68.3 before treatment which improved to 152.5, 138.2 and 198 after 2 weeks, 1 month and 2 months of treatment, respectively (P<0.001). Contrast sensitivity may provide better assessment of visual function as compared to visual acuity. Changes in contrast sensitivity are more sensitive to occlusion therapy as compared to visual acuity. Therefore, contrast sensitivity may yield better evaluation of subclinical changes not detectable by testing visual acuity.