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Archana Singh, Pesala Veerendranath, Prashant Garg, Shrikant Bharadwaj; The Impact Of Astigmatism On The Distance And Near Visual Acuity In Pseudophakic Eyes. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1386.
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Determining the visual impact of residual astigmatism in pseudophakic eyes is critical for the management of post-operative refractive error after cataract surgery. This study determined the impact of induced and habitual astigmatism on monocular distance and near acuity of pseudophakes with monofocal IOL implants.
Expt I: +2.5D myopic to -2.0D hyperopic astigmatism in 0.5D steps was induced along one of four axes (0º, 45º, 90º and 135º) by placing a trial lens over one eye (fellow eye was occluded) of 15 emmetropic pseudophakes (Mean+1SD: 57.9+9.0yrs), after five weeks or more of uncomplicated cataract surgery. High contrast distance (4m) and near (40cm) logMAR acuity was recorded for each combination of lens power and axis. Expt II: Monocular distance and near acuity and pupil size was recorded in 41 pseudophakes (60.9+9.8yrs) with varying magnitudes of habitual residual astigmatism after uncomplicated cataract surgery.
Mean (+1SD) uncorrected distance and near acuity was -0.06+0.08 and +0.6+0.15, respectively in Expt I and +0.21+0.19 and +0.55+0.20, respectively, in Expt II. Distance acuity reduced monotonically with increasing astigmatism (p<0.001) for all axes tested (p=0.52), more so in induced myopic than in induced hyperopic condition (p<0.05 for all). Near acuity did not change with induced hyperopic astigmatism (p>0.1) while it improved significantly with up to +1D of induced myopic astigmatism (p<0.001), before saturation for all axes tested (p=0.66). The loss in distance acuity with 1D and 2D of induced myopic astigmatism was poorly correlated with the corresponding gain in near acuity for all axes tested (r<0.15, p>0.05 for both). The overall trend in distance and near acuity with habitual astigmatism in Expt II was similar to that of Expt I. The near acuity for a given magnitude of astigmatism, however, varied with pupil size, with smaller pupils showing better near acuity than larger pupils.
Near acuity of pseudophakic eyes changes with both the magnitude of astigmatism and pupil size. Improved near acuity with myopic astigmatism is associated with a proportional loss in distance acuity for all axes tested. The monotonic loss in distance acuity and the saturation of near acuity suggests that visual experience of pseudophakes with myopic astigmatism >1D may be sub-optimal with a large loss of distance acuity and no additional benefit to near vision.
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