Peripheral Aberrations and Image Quality for Contact Lens Correction

Abstract

Purpose Contact lenses reduced the degree of hyperopic field curvature present in myopic eyes and rigid contact lenses reduced sphero-cylindrical image blur on the peripheral retina, but their effect on higher order aberrations and overall optical quality of the eye in the peripheral visual field is still unknown. The purpose of our study was to evaluate peripheral wavefront aberrations and image quality across the visual field before and after contact lens correction. Methods A commercial Hartmann-Shack aberrometer was used to measure ocular wavefront errors in 5° steps out to 30° of eccentricity along the horizontal meridian in uncorrected eyes and when the same eyes are corrected with soft or rigid contact lenses. Wavefront aberrations and image quality were determined for the full elliptical pupil encountered in off-axis measurements. Results Ocular higher-order aberrations increase away from fovea in the uncorrected eye. Third-order aberrations are larger and increase faster with eccentricity compared to the other higher-order aberrations. Contact lenses increase all higher-order aberrations except 3rd-order Zernike terms. Nevertheless, a net increase in image quality across the horizontal visual field for objects located at the foveal far point is achieved with rigid lenses, whereas soft contact lenses reduce image quality. Conclusions Second order aberrations limit image quality more than higher-order aberrations in the periphery. Although second-order aberrations are reduced by contact lenses, the resulting gain in image quality is partially offset by increased amounts of higher-order aberrations. To fully realize the benefits of correcting higher-order aberrations in the peripheral field requires improved correction of second-order aberrations as well.

Spherical Aberration and the Sign of Defocus

“…Levels of coma (C 3 1 = 0.5 Km) and astigmatism (1 D) were selected to be representative of the human eye at 30 degrees in the periphery. 40,41 The main effect of adding astigmatism is to reduce the peak contrast and flatten the curve's profile within the interval of Sturm. However, the essential asymmetry about the y-axis is little affected by astigmatism or coma or both.…”

“…42 This task would be simplified in wide-field applications by the fact that eyes with a positive SA in the fovea also have a positive SA in the periphery, which also changes in the negative direction with accommodation. 41,43,44 Therefore, although the defocus sign cue generated by SA changes with accommodation, it will have the same sign across the retina. These contrast cues in the peripheral visual field cannot be dismissed on the grounds that visual acuity declines rapidly with retinal eccentricity because contrast sensitivity for pattern detection remains greater than unity for spatial frequencies well beyond the resolution limit.…”

Central and Peripheral Autorefraction Repeatability in Normal Eyes

“…17 This might be due to increased higher-order aberrations at more eccentric locations of the visual field when light travels through the peripheral cornea and crystalline lens. 28 Despite taking great care to ensure that the Grand Seiko measurement beam was centered in the pupil before taking measurements, subtle misalignment errors not detected by the examiner may have contributed to the increased variability observed in the far periphery.…”

Sign-Dependent Sensitivity to Peripheral Defocus for Myopes due to Aberrations

“…The WASCA is based on the Hartmann-Shack technique, which has been used extensively for peripheral aberration measurements, for example by Lundström et al, Mathur et al, and Shen and Thibos. 10,11,39 These wavefront measurements took place 6 months after the psychophysical measurements. We contacted only subjects whose psychophysical measurements had been classified as reliable.…”