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A. Nieto-Bona, C. Palomo-Álvarez, J. Carballo-Álvarez, M. C. Puell Marín; Visual Performance of LASIK Patient. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1990.
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To evaluate the effects of corneal asphericity, ablation depth and spherical equivalent previous surgery on the high contrast visual acuity (HCAV), on the low contrast visual acuity (LCVA) and the accommodation amplitude.
A multicentric and retrospective study was performed on patients who underwent surgery at four refractive surgery clinics. All LASIK procedures were conducted by an experienced surgeon using standard laser ablation nomograms (Visx Star S2, LADARVision 4000, Technolas 270 and Visx Star S4). The surgical procedure was a superior-hinge created using a Hansatome microkeratome on 26 eyes and a nasal-hinge using a Moria microkeratome on 10 eyes. Patients were evaluated at the Optometry Clinic of the Complutense University (Madrid, Spain). Inclusion criteria were: a presurgery spherical equivalent of less than -8.00 D (myopia ≤ 6D., cylinder < 2.00), age 25-45 years, normal ocular health and refractive surgery 6 to 36 months previously. Visual acuity was measured using high contrast (96%) and low contrast (5%) logMAR charts under photopic conditions. Accommodation amplitude was measured monocularly using 2 subjective approaches - the push up test and minus lenses to blur-using their best correction at distance. Corneal asphericity was evaluated using the Zeiss Humprey System Atlas. Pre- and post surgery corneal thickness and depth of ablation data were obtained from a clinical database.
High and low contrast visual acuity were lower than in the general population with the same ages. There were correlations between corneal asphericity post LASIK and HCVA (p= 0,02) and LCVA (p = 0,03), respectivaly. So, LCVA presented significant correlations with depth of ablation, with their previous spheric equivalent and also according to the time since the surgery. Accomodation amplitude was different with each method used (p =0.0000) and both values was lower than normal values. This decrease was not linked in any way with the variables analyzed in the study.
The increase in corneal asphericity produces more deterioration on low contrast visual acuity, which is greater with a higher degree of myopia. Time since surgery also decreased low contrast visual acuity.
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