Abstract
Abstract: :
Purpose: To evaluate the utility of low– to medium– spatial frequency letter contrast sensitivity (CS) as a measure of visual function during amblyopia therapy. Methods: Statistical analysis of a dataset of log letter CS (Pelli–Robson) and logMAR visual acuity (VA) obtained from the Monitored Occlusion Treatment of Amblyopia Study, MOTAS (Br. J. Ophthalmol. 2002;86:915–9). Results: Data were analysed for 46 children with amblyopia with a total of 370 paired measurements of logMAR VA and letter CS. A weak relationship between log letter CS and logMAR VA was observed for all acuities better than 0.90 logMAR. For acuities of 0.90 logMAR or poorer, log letter CS appeared to decrease monotonically with declining VA. Bootstrap resampling of the dataset confirmed these observations: log letter CS was weakly, but significantly correlated with logMAR VA (r=–0.247, 95% CI: –0.350 to –0.139) for all VAs better than 0.90 whereas for VAs of 0.90 logMAR or poorer, log letter CS was markedly and significantly correlated with VA (r=–0.740, 95% CI: –0.819 to –0.520). During the course of amblyopia therapy (non–overlapping phases of refractive adaptation and occlusion therapy) mean (SD) log letter CS improved by 0.09 (0.24) and 0.07 (0.11) log units in the respective treatment phases. In contrast, mean (SD) logMAR VA improved by 0.19 (0.14) and 0.24 (0.15) log units. Conclusions: Low– to medium– spatial frequency letter CS appears, relative to logMAR VA, to be insensitive in detecting change in mild to moderate amblyopic deficits and therefore its inclusion within a test battery monitoring the effects of treatment is questionable. Only where the deficit in resolution is marked is this reflected in a clinically significant reduction in letter CS. This observation suggests that CS at low– to medium– spatial frequencies is independent of any defict in resolution at higher spatial frequencies. Only where resolution is impaired within the low– to medium range of spatial frequencies is a concomitant reduction in CS likely to be present.
Keywords: amblyopia • visual acuity • contrast sensitivity