title: Treatment of halos after photorefractive keratectomy.
abstract: BACKGROUND
  Some patients, despite a good visual outcome after photorefractive keratectomy (PRK), have severe problems with halos.
  
  
  METHODS
  Ten eyes with a near-plano refraction after PRK were treated again with PRK to reduce halos. The goal of the second surgery was to enlarge the diameter of the treatment zones without changing the refraction obtained by the first surgery. The treatment zone was enlarged from 5 or 6 mm to 7 mm. In eyes in which a multizone technique was used in the first PRK, the amount of correction was increased in the transition zone. However, the refractive power in the central 4 or 5-mm zone was not altered. This result was obtained by calculating the amount of desired increased correction on a large zone (6 or 7 mm) and then for the same amount on a smaller zone (4 or 5 mm). The latter, which would produce changes of curvature in the central zone, is subtracted from the overall treatment. Only the part of the treatment where the laser beam increased from 4 or 5 mm to 6 or 7 mm was delivered to the eye. In this process, only the peripheral zones were modified. The central 4 or 5 mm zone was deepened but its curvature and the refraction remained the same.
  
  
  RESULTS
  A decrease of symptoms was noticed by seven of the ten patients. In all eyes, the refraction obtained by the initial surgery was not significantly changed by the second surgery. The best results were obtained in milder myopic patients who had their first surgery with a small diameter ablation zone.
  
  
  CONCLUSIONS
  Halos can be reduced by repeating the PRK and by increasing the treatment zone without changing the refraction obtained by the first PRK.
authors.affiliation: Department of Ophthalmology, Centre de Hospitalier l'Université Laval, Québec, Canada.
authors.forename: G
authors.initials: G
authors.lastname: Lafond
mesh_terms: D003315:Cornea / Q000601:surgery; D006801:Humans; D007091:Image Processing, Computer-Assisted; D054018:Lasers, Excimer; D008027:Light; D009216:Myopia / Q000601:surgery; D009887:Ophthalmoscopy; D018903:Photorefractive Keratectomy / Q000009:adverse effects / Q000379:methods*; D011183:Postoperative Complications / Q000209:etiology / Q000628:therapy*; D012086:Reoperation; D016896:Treatment Outcome; D014786:Vision Disorders / Q000209:etiology / Q000628:therapy*; D014792:Visual Acuity