title: Anterior corneal optical aberrations induced by photorefractive keratectomy for hyperopia.
abstract: OBJECTIVE
  Photorefractive keratectomy (PRK) for hyperopia requires both a steepening of the central cornea and a flattening of the mid-periphery to achieve its effect and is likely to affect the optical aberrations of the eye.
  
  
  METHODS
  Nine patients underwent PRK to correct between +2.00 and +4.00 D of hyperopia (first eye treated for each patient) using the Summit Technology Apex Plus excimer laser. Anterior corneal aberrations for pupil diameters of 3, 5.5 and 7 mm were estimated from corneal topography data (TMS-1), assuming a uni-index, single surface cornea. Refractive error was assessed using retinoscopy and standard subjective tests.
  
  
  RESULTS
  Apart from the intended change in refraction (mean spherical equivalent manifest refraction, +4.60 +/- 1.60 D before surgery and +0.70 +/- 1.60 D at 1 year after surgery), the most significant change was in spherical aberration. Anterior corneal spherical aberration was positive (+1.60 +/- 0.60 D for a 5.5-mm pupil) before surgery and became negative after surgery (-1.80 +/- 1.20 D at 1 year). The change in spherical aberration was related to the achieved change in refractive error.
  
  
  CONCLUSIONS
  The large change (approximately 3.00 D) in spherical aberration (from positive to negative aberration) has implications for the optical performance of the whole eye, where the effects of lenticular aberration must also be considered.
authors.affiliation: Department of Vision Sciences, Glasgow Caledonian University, UK. K.Oliver@gcal.ac.uk
authors.forename: K M
authors.initials: KM
authors.lastname: Oliver
authors.forename: D P
authors.initials: DP
authors.lastname: O'Brart
authors.forename: C G
authors.initials: CG
authors.lastname: Stephenson
authors.forename: R P
authors.initials: RP
authors.lastname: Hemenger
authors.forename: R A
authors.initials: RA
authors.lastname: Applegate
authors.forename: A
authors.initials: A
authors.lastname: Tomlinson
authors.forename: J
authors.initials: J
authors.lastname: Marshall
mesh_terms: D003315:Cornea / Q000473:pathology* / Q000601:surgery; D019781:Corneal Topography; D006801:Humans; D006956:Hyperopia / Q000601:surgery*; D054018:Lasers, Excimer; D009216:Myopia / Q000175:diagnosis / Q000209:etiology*; D018903:Photorefractive Keratectomy / Q000009:adverse effects*; D012029:Refraction, Ocular; D014792:Visual Acuity