Topographical analysis of ablation centration after excimer laser photorefractive keratectomy and laser in situ keratomileusis for high myopia

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Abstract
Purpose: To evaluate the ablation centration after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) for high myopia and to assess the association between decentration and best corrected visual acuity (BCVA), glare, monocular diplopia, and halo phenomenon. Setting: Mater Private Hospital, Dublin, Ireland. Methods: Corneal topography was used to analyze centration in two groups of patients with myopia of more than 6.0 diopters: 18 had PRK and 18, LASIK. A standardized questionnaire assessed the preoperative and postoperative prevalence of glare, monocular diplopia, and halo phenomenon. Results: “Significant” ablation decentration (0.5 mm) in the LASIK group (1.33 mm) was almost twice that in the PRK group (0.75 mm). Glare increased from 27% preoperatively to 42% in the PRK group; monocular diplopia increased in the LASIK group. Halo phenomenon decreased after both procedures. Conclusion: Laser in situ keratomileusis represents a step forward in the surgical correction of high myopia, but the accuracy of the corneal ablation location must be improved. Suction ring fixation of the globe or real time tracking systems may help improve centration.