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Abstract
The purpose of the work was to assess the contrast sensitivity function of individuals wearing gas permeable (GP) multifocal contact lenses, soft bifocal contact lenses, and GP monovision lenses. Twenty-six females and six males between the ages of 42 and 65 participated in this study. The study included subjects wearing monovision (N = 8), the Acuvue Bifocal (Johnson & Johnson) (N = 8), Essential GP Multifocal (Blanchard) lenses (N = 8) and progressive addition spectacle lenses (PAL) (N = 8), with PAL wearers forming the control group. Measurements of binocular contrast sensitivity were obtained using the VISTECH 6500 system. Thresholds for each spatial frequency were fit to the equation CS(k) = ak exp(−bk) [1 + c exp(bk)]−1/2, to describe the human contrast sensitivity function. The area under the contrast sensitivity function (CSF) curve was calculated for all four groups and compared. An index of performance was obtained, which was defined as the ratio of CSF with the contact lens correction to the CSF with spectacles. Of the contact lens wearing groups, GP multifocal contact lens wearers had the highest contrast sensitivity at all the spatial frequencies. Soft bifocal contact lens wearers exhibited higher contrast sensitivity than monovision wearers at all spatial frequencies. Subjects wearing GP multifocals had the largest area under the CSF; followed by those wearing soft bifocals, with monovision wearers having the smallest area. GP multifocals have the best visual function at 0.98, soft bifocals have an index of 0.65 and monovision has an index of 0.59. This study quantifies the visual performance of the three lens systems by measuring the area under the CSF curve. In addition, it provides indices of visual function with the contact lenses that will be helpful for analyses and comparisons in future studies.
Acknowledgements
The authors would like to thank all the subjects who participated in this study. Presented in part at the Annual Meeting of the American Academy of Optometry, Dallas, Texas, December 2003 [Optom. Vis. Sci. 80 (12s) 194 (2003)].