Effect of Difference of Binocular Retinal Illuminance on Stereopsis

PURPOSE: We examined the effect of induced interocular difference of retinal illuminanace on stereopsis. METHODS: Fifty adults who have normal binocularity were examined with neutral density filters. The mean age was 29.1 years. While the monocular retinal illuminance was gradually reduced by increasing the value of neutral density filters, we measured the best corrected visual acuity and stereoacuity with Titmus test and Lang test. We used neutral density filter from 1.0 neutral density (ND, 10% transmit) to 3.0ND (0.1% transmit) with intervals of 0.2ND. RESULTS: The best corrected visual acuity began to decrease significantly when the value of neutral density filter reached 2.0ND (1% transmit). Stereoacuity also began to decline when the value was 1.4ND(4% transmit) with Titmus test and 1.6ND (2.5% transmit) with Lang test. CONCLUSIONS: Change of retinal illuminance effects more on stereoacuity than visual acuity as stereoacuity decreased earlier by increasing the value of density filters. These results imply that the stereopsis test could be more useful than visual acuity test for detecting ocular abnormalities influencing the retinal illuminance.

Effects of Retinal Illuminance on Visual Acuity and Fusion

PURPOSE: We examined the effects of induced retinal illuminance on visual acuity and fusion. METHODS: Fifty adults with best corrected visual acuity of 20/20 or better and normal binocularity and fusion were examined. To examine the effect of retinal illuminance on visual acuity and the effect of binocular difference of retinal illuminance on fusion, we used neutral density filter from 0.1 ND to 4.0 ND. While neutral density filter values were increased, we measured the least size fusion slide by major amblyoscope as well as the best corrected visual acuity. RESULTS: The best corrected visual acuity and the level of fusion were decreased significantly when monocular retinal illuminance was reduced to 2.0 ND (P<0.01, P<0.01, respectively). Although the visual acuity and fusion were equally influenced by retinal illuminance, the effect on fusion was more prominent when retinal illuminance decreased greatly. CONCLUSIONS: These results will be of help for the prevention and early detection of amblyopia, although further study will be needed in order to fully evaluate the influences of other factors on binocular fusion.