Myopia Research Today is a free monthly online journal that collates and summarizes the latest research about Myopia, including details on treatment, prevention, causes, correction. | ||||||||
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Effects of ablation diameter on long-term refractive stability and corneal transparency after photorefractive keratectomy.Rajan MS, O'Brart D, Jaycock P, Marshall J Department of Academic Ophthalmology, St. Thomas' Hospital, London, United Kingdom. msrajan@tiscali.co.uk OBJECTIVE: To evaluate the effects of ablation diameter on long-term refractive stability and corneal transparency after photorefractive keratectomy (PRK). DESIGN: Long-term, prospective, follow-up study. PARTICIPANTS: One hundred twenty-three eyes treated between 1990 and 1993 at one institution as part of a number of ethical committee-approved clinical studies underwent long-term follow-up at 10 to 12 years after PRK. INTERVENTION: Photorefractive keratectomy was performed using the Summit Technology UV 200 and OmniMed Excimer lasers with either 4.0-mm (n = 36), 5.0-mm (n = 47), or 6.0-mm (n = 40) optical zones and either -3.0-diopters (D) or -6.0-D myopic spherical corrections, based on the original Munnerlyn algorithms. MAIN OUTCOME MEASURES: Refractive stability, refractive predictability, best spectacle-corrected visual acuity, and corneal haze. RESULTS: Refractive outcome at 1 and 10 to 12 years of follow-up was better with 6.0-mm treatments, especially for -6.0-D corrections (P>0.001). The early hyperopic shift was significantly reduced with 6.0-mm zones, with less regression between 1 and 6 months, compared with 5.0- and 4.00-mm PRK, especially for -6.0-D corrections (P<0.001). The postoperative refraction remained stable between 1 and 10 to 12 years in all groups. Objective measurements of haze were less with 6.0-mm compared with 4.0- and 5.0-mm treatments (P<0.001). Night vision problems were significantly less with 6.0-mm PRK (P<0.01). There was no evidence of progressive hyperopic shift, corneal ectasia, or late onset of corneal haze in any of the eyes during the follow-up period. CONCLUSIONS: Refractive stability was maintained between 1 year and 10 to 12 years after PRK with 4.0-, 5.0-, and 6.0-mm optical zones. A significant linear trend was observed in terms of refractive predictability, early hyperopic shift, regression, corneal transparency, and night haloes with better outcomes in PRK with a larger ablation zone. None of the eyes had sight-threatening complications such as ectasia or late-onset corneal haze during the follow-up. Published 2 October 2006 in Ophthalmology, 113(10): 1798-806.
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