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ED Weichel, KS Bower, E Morgan, J Rabin; Visual Performance in Photorefractive Keratectomy: One Year and Beyond . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4149.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The efficacy of refractive surgery typically is based on the level of high contrast visual acuity (VA) achieved and the degree of post-operative, residual refractive error. While decrements in contrast sensitivity (CS) and other measures of visual performance have been demonstrated, these effects are often transient, and not consistently related to visual symptoms. Moreover, information about long-term effects on visual function is lacking. We describe comprehensive measures of visual performance in photorefractive keratectomy (PRK) one year or more after surgery. Methods: Subjects were active duty Army soldiers treated for myopia (-1 to -5D) with a VISX Star excimer laser (6 mm ablation zone) at least one year ago. VA versus contrast (1.25% to 100%) and small letter CS were measured at photopic and mesopic light levels. Glare disability was assessed for mesopic VA (2.5 and 5% contrast) and mesopic small letter CS. Complete spatial and temporal sine-wave CS functions were obtained at photopic and mesopic levels, using a computer-controlled, 2-alternative forced choice system. Results: At 12-18 months after PRK, uncorrected VA for a range of contrasts (2.5%, 10% and 100%) was not significantly different from pre-operative VA with best correction (p≷0.1), despite correction for post-operative magnification effects. Whereas small target CS, and spatial and temporal CS were largely within normal limits, there was considerable inter-subject variability (≷0.2 log units), with some subjects falling below normal levels. In some cases performance decrements were related to higher order aberrations. Conclusion: Comprehensive visual assessment, including target detection and recognition with static and dynamic displays, at normal and reduced luminance, is necessary to fully characterize visual performance in refractive surgery. Further testing is underway to determine how higher order aberrations, pupil size and other factors account for decrements in visual performance detected with this methodology.
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