title: Corneal topography of excimer laser photorefractive keratectomy using a 6-mm beam diameter. Summit PRK Topography Study Group.
abstract: 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.
  
  
  METHODS
  Multicenter, prospective cohort study.
  
  
  METHODS
  Ninety-eight eyes of 90 patients with myopia who had undergone PRK using the Summit Technology, Inc., excimer laser with a 6-mm beam diameter.
  
  
  METHODS
  Computer-assisted videokeratography data were analyzed for eyes having undergone PRK. Topography patterns at 3, 6, and 12 months after surgery were classified and associations with clinical outcomes assessed.
  
  
  METHODS
  Topography patterns after PRK were determined at 3, 6, and 12 months after surgery. Associations with preoperative characteristics of age and attempted correction, and postoperative outcomes of uncorrected and spectacle-corrected visual acuity, predictability, astigmatism, corneal haze, glare, halo, and patient satisfaction were analyzed.
  
  
  RESULTS
  At 1 year, 21.4% of corneas showed a homogeneous topography, 27.6% showed a toric-with-axis configuration, 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 months, 40.1% of maps changed; from 6 to 12 months, 53.1% of maps changed, generally to optically smoother, regular patterns. Older age and higher attempted correction were associated with the development of more irregular patterns. The irregular groups showed worse predictability than did the regular groups and a tendency for slight overcorrection. The average reported glare/halo of 1.33 (scale = 0 to 5) in this study was less than in a previous study of the 4.5- to 5-mm treatment zone. However, of six patients expressing dissatisfaction with the results of surgery, three ranked their glare or halo at the maximum level.
  
  
  CONCLUSIONS
  Topography patterns using a 6-mm beam diameter are identifiable, improve with time, and may affect clinical outcomes after photorefractive keratectomy (PRK). The keyhole/semicircular pattern is more prevalent with a 6 mm treatment zone than with smaller treatment zones. Although optical side effects of glare and halo appear to be reduced with the 6-mm treatment, a small number of patients still report substantial glare or halo after the procedure.
authors.affiliation: Department of Ophthalmology, UMDNJ-New Jersey Medical School, Newark 07103, USA.
authors.forename: P S
authors.initials: PS
authors.lastname: Hersh
authors.forename: S I
authors.initials: SI
authors.lastname: Shah
mesh_terms: D001251:Astigmatism / Q000503:physiopathology; D015331:Cohort Studies; D003315:Cornea / Q000473:pathology* / Q000601:surgery*; D005500:Follow-Up Studies; D005544:Forecasting; D019466:Glare; D006801:Humans; D053685:Laser Therapy; D054018:Lasers, Excimer; D017060:Patient Satisfaction; D018903:Photorefractive Keratectomy; D011184:Postoperative Period; D011446:Prospective Studies; D012029:Refraction, Ocular; D013997:Time Factors; D014792:Visual Acuity