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EJ Casson, T Wong, E Swanson; A Comparison of Visual Performance Tests in Normals and Refractive Surgery Patients . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3839.
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Purpose: A number of different assessment techniques have been used to investigate losses in low contrast vision associated with refractive surgery. These include grating tests, letter based tests and low contrast acuity tests. Yet little is known about how the results of these tests compare in this patient population. Methods: We investigated this by assessing a group of normals (20 eyes) and patients who had PRK surgery for myopia at least 4 years previous (50 eyes) with the Regan Low Contrast Acuity charts(96, 25 and 11%), the Pelli Robson Contrast Sensitivity chart and the Vistech grating chart. All subjects were assessed under bright viewing conditions with natural and dilated pupils. Testing was carried out in the same order in both groups. Results:The average age and refractive error of the two groups was similar (NL= 52.0 yrs, -0.38D; PRK=49.5 yrs, -1.10D). The overall results demonstrated that there are significant differences (p<.001) between the NL group and the PRK group under dilated conditions on all assessment procedures. PRK eyes have poorer results than normals on the Regan 11% chart, the Pelli Robson and the Vistech D Grating series. To compare results across tests, we normalized the PRK scores on the three test types. The greatest average normalized reduction in visual performance was found for the Vistech D grating (-4.38), followed by the Regan 11% chart (-3.18) and the Pelli Robson (-0.88). The highest inter-test correlations in visual performance score were found between the 11% Regan Charts and the Vistech D grating (NL, r2=0.32, PRK r2=0.44). Conclusion: The Regan 11% contrast acuity chart and the Vistech D gratings demonstrate more sensitivity for assessing PRK patients than the Pelli Robson. This may be due to the nature of vision changes with refractive surgery.
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