CORNEAL TOPOGRAPHY OF EXCIMER-LASER PHOTOREFRACTIVE KERATECTOMY USINGA 6-MM BEAM DIAMETER

Objective: The purpose of the study is to define qualitative patterns of corneal topography after excimer laser photorefractive keratectomy (PRK) using a 6-mm beam diameter, investigate changes in patterns over time, and identify associations of topography patterns with clinical outcomes. Design: Multicenter, prospective cohort study. Participants: Ninety-eight eyes of 90 patients with myopia who had undergone PRK us ing the Summit Technology, Inc., excimer laser with a 6-mm beam diamet er.Intervention: Computer-assisted videokeratography data were analyze d for eyes having undergone PRK. Topography patterns at 3, 6, and 12 m onths after surgery were classified and associations with clinical out comes assessed. Main Outcomes Measured: Topography patterns after PRK were determined at 3, 6, and 12 months after surgery. Associations wit h preoperative characteristics of age and attempted correction, and po stoperative outcomes of uncorrected and spectacle-corrected visual acu ity, predictability, astigmatism, corneal haze, glare, halo, and patie nt satisfaction were analyzed. Results: At 1 year, 21.4% of corneas sh owed a homogeneous topography, 27.6% showed a toric-with-axis configur ation, 10.2% showed a toric-against-axis configuration, 7.1% showed an irregularly irregular topography, 24.5% showed a keyhole/semicircular pattern, and 9.2% showed focal topographic variants. From 3 to 6 mont hs, 40.1% of maps changed; from 6 to 12 months, 53.1% of maps changed, generally to optically smoother, regular patterns. Older age and high er attempted correction were associated with the development of more i rregular patterns. The irregular groups showed worse predictability th an did the regular groups and a tendency for slight overcorrection. Th e average reported glare/halo of 1.33 (scale = 0 to 5) in this study w as less than in a previous study of the 4.5- to 5-mm treatment zone. H owever, of six patients expressing dissatisfaction with the results of surgery, three ranked their glare or halo at the maximum level. Concl usions: Topography patterns using a 6-mm beam diameter are identifiabl e, improve with time, and may affect clinical outcomes after photorefr active keratectomy (PRK). The keyhole/semicircular pattern is more pre valent with a 6 mm treatment zone than with smaller treatment zones. A lthough optical side effects of glare and halo appear to be reduced wi th the 6-mm treatment, a small number of patients still report substan tial glare or halo after the procedure.