title: Biologic and environmental risk factors for regression after photorefractive keratectomy.
abstract: OBJECTIVE
  After photorefractive keratectomy (PRK), the final refraction in the majority of patients is near the intended refraction. However, a significant proportion of patients show regression, which is commonly associated with corneal haze. This study aims to determine whether biologic and environmental factors influence the outcome of PRK.
  
  
  METHODS
  One hundred patients prospectively underwent -3.00- or -6.00-diopter corrections. Three months after surgery, 100% of patients answered a questionnaire that recorded their biologic characteristics, medical and ocular history, and postoperative exposure to physical and chemical insults. Multivariable analysis identified those factors associated with regression.
  
  
  RESULTS
  Multivariable analysis showed that the risk of regression was increased significantly in patients who underwent higher dioptric or smaller diameter treatments (P = 0.045) and in those who had had regression after treatment of the first eye (P = 0.019). There was no difference between the sexes, but regression was 13.5 times more likely in females who were taking oral contraceptives. Regression was increased in those exposed to solar radiation (odds ratio, 7.6; 95% confidence interval, 1.82-32.22) and sun beds (odds ratio, 2.4; 95% confidence interval, 0.64-9.39), and was significantly greater in patients with ocular-surface disorders (on univariable analysis only; P = 0.034). Regression was not associated with previous contact lens wear, swimming, cigarette smoking, or minor ocular trauma.
  
  
  CONCLUSIONS
  The questionnaire identified biologic and environmental risk factors for regression. The biologic risk factors may be used preoperatively to counsel patients and, where necessary, advise them against surgery. The environmental risk factors are largely avoidable by modification of patient behavior.
authors.affiliation: Department of Ophthalmology, St. Thomas' Hospital, London, England, UK.
authors.forename: M C
authors.initials: MC
authors.lastname: Corbett
authors.forename: D P
authors.initials: DP
authors.lastname: O'Brart
authors.forename: F G
authors.initials: FG
authors.lastname: Warburton
authors.forename: J
authors.initials: J
authors.lastname: Marshall
mesh_terms: D000328:Adult; D003315:Cornea / Q000503:physiopathology* / Q000601:surgery; D004777:Environment; D005260:Female; D006801:Humans; D054018:Lasers, Excimer; D008297:Male; D015999:Multivariate Analysis; D018903:Photorefractive Keratectomy; D011183:Postoperative Complications / Q000503:physiopathology* / Q000517:prevention & control; D011446:Prospective Studies; D012030:Refractive Errors / Q000503:physiopathology* / Q000517:prevention & control; D054140:Refractive Surgical Procedures; D012307:Risk Factors; D011795:Surveys and Questionnaires; D016896:Treatment Outcome