Abstract
Purpose: :
Our previous study has shown that second order Zernike astigmatism in myopic eyes was reduced when rigid-gas-permeable contact lens (RGP-CL) was worn (Lu et al. OVS 2003). The purpose of this study was to test its visual effect of the astigmatism correction during RGP-CL wearing.
Methods: :
Wavefront aberrations of twenty one myopic eyes with astigmatism greater than -0.5D (mean=-0.93±0.38D) were measured using a wavefront sensor (WASCA, Carl Zeiss Meditec) under four conditions: corrected for spherical equivalent with (1) spectacle lens (SL), (2) soft-contact lens (Soft-CL, Surevue, J&J) and (3) rigid-gas-permeable contact lens (RGP-CL, XO, Boston) and fully corrected for both spherical error and astigmatism with (4) spectacle lens (fSL). Both contrast visual acuity (VA) at 100%, 25%, 10% and 5% contrast levels (MFVA-100, Shenzhen BriteEye) and contrast sensitivity function (CSF) at 3, 6, 12 and 18 cpd (CSV-1000E, Vectorvision) were also assessed for the subjects under the same correction conditions as in the wavefront measurement. Difference in contrast VA and CSF under the RGP-CL wear condition from the other three correction conditions was statistically tested.
Results: :
Mean root-mean-square of total wavefront aberrations from 2nd order up to 7th order at a 6.0mm pupil size for the 21 eyes were 1.09±0.36, 0.88±0.35, 0.63±0.20 and 0.47±0.17µm under the SL, Soft-CL, fSL and RGP-CL conditions respectively. Contrast VA under the RGP-CL condition was significantly improved by a mean of 0.11 and 0.09 logMAR across the 4 contrast levels from those under SL and Soft-CL conditions respectively. The difference in mean contrast VA between the RGP-CL and fSL was only 0.01 logMAR. RGP-CL wear gained mean contrast sensitivity across the four spatial frequencies by 0.14, 0.08 and 0.04 log units against the SL, Soft-CL and fSL wearing conditions. The difference in mean contrast VA between the RGP-CL and the Soft-CL conditions was close to that between fSL and SL conditions (0.09 vs. 0.10 logMAR).
Conclusions: :
RGP-CL wear corrects astigmatism in myopic eyes and also improves visual performance with the effect compatible with that from astigmatism correction provided by spectacle lens.
Keywords: contact lens • visual acuity • contrast sensitivity