Potential vision testing--the relationship between visual acuity and Vernier acuity in the presence of simulated...

To evaluate the utility of a computer controlled two-bar Vernier acuity measurement as a predictor of visual function in the presence of cataract we measured logMAR visual acuity and Vernier acuity in a group of 40 young normal observers under various levels of dioptric blur (0-3 D in dioptre steps). The Vernier thresholds were resistant to dioptric blur up to 2 D, but performance degraded with blur of 3 D for non-optimised Vernier stimulus parameters. The stimulus parameters, bar length and bar separation, were further investigated in two subjects under conditions of blur. By extending the Vernier bar length and increasing the bar separation the effect of blur could be further reduced even under the most blurred condition. The relationship between visual acuity and Vernier acuity was determined. Vernier acuity was measured in the presence of Vistech cataract simulating lenses and a prediction of visual acuity was made for three observers, two with no ocular abnormality and one with age-related maculopathy. The cataract simulating lenses affected the measured visual acuity in all three subjects, but had less effect on Vernier acuity. Predicted visual acuities were all within six letters (0.12 log units) of the visual acuity without the simulated cataract. As expected, the subject sufferng from age-related maculopathy, whilst showing similar levels of Vernier acuity to the two ocularly healthy subjects at 1.5 degrees of retinal eccentricity, showed much poorer Vernier acuity for stimuli presented at fixation.