Abstract
Purpose :
Psychophysical experiments in adult amblyopes indicate that amblyopia affects ON more than OFF visual pathways making it more difficult to see white stimuli on black background. However, conventional measurements of visual acuity (VA) in children use black letters on white background that cannot reveal these ON-pathway deficits. This study tests the hypothesis that measurements of visual acuity with white optotypes on black background are more sensitive in detecting amblyopia than black optotypes on white background.
Methods :
Two groups of children (ages 8-12) were enrolled. The amblyopic group (N=15 with strabismus and/or anisometropia) had a best-corrected VA of 20/40 or worse in the amblyopic eye with an interocular difference of ≥ 0.2 logMAR, and an acuity range of 20/40 - 20/400. The control group (N=8) had an interocular difference of < 0.2 logMAR and stereoacuity better than 100 arcsec. An electronic surrounded ETDRS VA program (M&S) with Amblyopia Treatment Study (ATS) protocol including white and black optotypes was calibrated to a screen luminance of 90-110 lux. Participants were tested monocularly at 3 meters viewing distance and their VA was reported as a letter score. The order of optotype polarity was randomized and the measurements were repeated at the time interval of half hour. A paired t-test was used to evaluate differences between visual acuity Scores of amblyopic eyes, fellow eyes, and control eyes, measured with white and black optotypes.
Results :
For amblyopic eyes, the mean Score was significantly different between optotypes of different polarity (61.57±11.55 for white optotypes vs 64.47±11.25 for black optotypes, t = 4.4, p < 0.001), indicating that the amblyopic eye had more difficulty seeing white than black optotypes. In comparison, no significant differences were found in control eyes (87.22±4.93 for white optotypes vs 86.60±4.06 for black optotypes, t = 0.73, p = 0.62), and the differences were marginally significant in fellow eyes (82.53±5.79 for white optotypes vs 84.07±6.97 for black optotypes, t = 2.2, p = 0.04).
Conclusions :
According to our pilot data, VA in amblyopic eyes is 3 letters (~0.06 logMAR) lower when measured with white optotypes than black optotypes, supporting our hypothesis that VA measurements with white optotypes are better at detecting amblyopia deficits in children with strabismic, anisometropic, or combined amblyopia.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.