The effect of refractive error on perimetric thresholds using the Humphrey Field Analyser

Abstract

Five normal young (20 ± 5 years) subjects had the central and peripheral fields of their right eyes measured using the Humphrey Field Analyser under emmetropic conditions and fitted with 38 per cent water content Hema spherical contact lenses to simulate distance refractive errors of 4 D, 6 D, 8 D, and 10 D of both myopia and hyperopia. The results for each induced refractive state were merged and averaged so that comparisons could be made with the averaged normal results. There was a mean decrease in sensitivity of 0.89 decibels (dB) per dioptre of uncorrected distance myopic refractive error or an estimated 1.27 dB per dioptre of myopic defocus (induced refractive error less 3 D due to the testing distance) for each of the 144 points for which thresholds were measured. For induced hyperopia, the mean decrease in sensitivity was 0.63 dB per dioptre of uncorrected distance refractive error or 1.01 dB per dioptre of estimated defocus (induced refractive error plus 3 D for the testing distance, less two-thirds of the accommodation). These reductions in sensitivity were significant centrally for 6 D or more of induced myopia (3 D or more of defocus) or 4 D or more of induced hyperopia (0.2 D or more of estimated defocus). Peripherally, the losses were significant in the temporal (and particularly inferior temporal) field for 6 D or more of induced myopia (3 D of defocus) and 4 D or more of induced hyperopia (0.2 D of estimated defocus). These results give ophthalmic practitioners a reference for use when assessing the peripheral fields of patients with high refractive errors.