Correction of Radial Astigmatism Improves Peripheral Contrast Sensitivity

Abstract

Abstract: : Purpose: The peripheral retina is the most sensitive retinal area under dim illumination, but the optical quality of the eye is reduced for off-axis viewing. Radial astigmatism in the periphery is uncorrected by the refraction for central vision. Peripheral contrast sensitivity has been shown to be affected by optical defocus at photopic light levels. The purpose of this study was to determine whether correction of peripheral astigmatism would enhance the visibility of spatial patterns at low luminance. Methods:Optical quality was measured on three adult subjects with the double-pass method, using 543 nm laser light and a 3mm artificial pupil. Retinal images were captured with a cooled CCD camera and a separate infrared viewing system was used to ensure that the laser beam entered the center of the subject’s pupil. Images were captured at the fovea in order to determine the optimum correction for central vision. Peripheral retinal images at 40° eccentricity were then captured, first at the dioptric focus for foveal vision, and then at the dioptric positions of the tangential and saggital line foci. Retinal images were then captured with a spectacle lens combination that corrected the peripheral radial astigmatism. Peripheral grating contrast sensitivity was measured with the natural pupil at two light levels (58 and 0.058 cd/m2), for each of the two refraction conditions: the conventional foveal correction and the correction for peripheral astigmatism. Results:Our subjects exhibited an average of about 4.00 Diopters of radial astigmatism in the periphery. When peripheral astigmatism was corrected, subjects gained an average of about 1 log unit in contrast sensitivity at 2 cyc/deg at the higher light level, and about 0.56 log unit at 2 cyc/deg at the lower light level. The improvement in contrast sensitivity was larger than the improvement in the modulation transfer function (MTF), because additional aberrations would have been present with the natural pupil. Conclusion:Correction of peripheral astigmatism provides considerable improvement in contrast sensitivity under natural viewing conditions. Hence, peripheral night vision could be enhanced by improving peripheral optical quality.

Keywords: 325 astigmatism • 519 physiological optics • 368 contrast sensitivity