Assessment of High and Low Contrast Visual Acuity after Photorefractive Keratectomy for Myopia

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Abstract
Our aim was to assess visual acuity using standardized charts and illumination conditions after photorefractive keratectomy. High and low contrast visual acuity were measured on Bailey-Lovie logarithm of the minimum angle of resolution (LogMAR) charts under high and low illumination conditions on 105 photorefractive keratectomy patients who had been treated with the Summit (N = 60) or the VISX (N = 45) excimer laser. Best corrected visual acuity was reduced in the treated eye compared with the untreated control eye under all test conditions, with the greatest differences under conditions of low contrast and low illumination. Reduction of acuity under low contrast and low illumination was related to small optic zone sizes and steep ablation edge profiles found in Summit-treated eyes. In the VISX-treated eyes, high contrast acuity was reduced in the presence of central topographical irregularities, subepithelial haze, and higher myopic corrections. Testing conditions such as those described here may be useful in quantifying vision degradation in suboptimal viewing conditions and among patients with vague complaints.

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