title: Recovery of corneal subbasal nerve density after PRK and LASIK.
abstract: OBJECTIVE
  To measure and compare the return of corneal innervation up to 5 years after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK).
  
  
  METHODS
  Prospective, nonrandomized clinical trial.
  
  
  METHODS
  Eighteen eyes of 12 patients received PRK to correct a mean refractive error of -3.73 +/- 1.30 diopters, and 16 eyes of 11 patients received LASIK to correct a mean refractive error of -6.56 +/- 2.44 diopters. Corneas were examined by confocal microscopy before and at 1, 2, 3, and 5 years after the procedures. Subbasal nerve fiber bundles were measured to determine density (visible length of nerve/frame area) and expressed as micrometers per square millimeters. Differences were compared by Friedman's test and adjusted for multiple comparisons by the Student-Newman-Keuls procedure.
  
  
  RESULTS
  After PRK, mean subbasal nerve density was reduced by 59% at 1 year (2764 +/- 1321 microm/mm(2) [+/-SD]) when compared with preoperative (6786 +/- 1948 microm/mm(2); P < .001). By 2 years, subbasal nerve density (6242 +/- 1763 microm/mm(2)) was not significantly different from density before PRK and remained unchanged to 5 years (5903 +/- 3086 microm/mm(2)). After LASIK, subbasal nerve density was reduced by 51%, 35%, and 34% at 1, 2, and 3 years, respectively (P < .001). By 5 years, subbasal nerves had returned to densities (4441 +/- 2819 microm/mm(2)) that were not significantly different from densities before LASIK (5589 +/- 2436 microm/mm(2)).
  
  
  CONCLUSIONS
  Corneal subbasal nerve density does not recover to near preoperative densities until 5 years after LASIK, as compared with 2 years after PRK.
authors.affiliation: Department of Ophthalmology, Mayo Clinic College of Medicine, Rochester, Minnesota.
authors.forename: Jay C
authors.initials: JC
authors.lastname: Erie
authors.forename: Jay W
authors.initials: JW
authors.lastname: McLaren
authors.forename: David O
authors.initials: DO
authors.lastname: Hodge
authors.forename: William M
authors.initials: WM
authors.lastname: Bourne
mesh_terms: D000328:Adult; D003315:Cornea / Q000294:innervation*; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D054018:Lasers, Excimer; D008137:Longitudinal Studies; D008297:Male; D018613:Microscopy, Confocal; D008875:Middle Aged; D009216:Myopia / Q000601:surgery*; D009412:Nerve Fibers / Q000502:physiology; D009416:Nerve Regeneration / Q000502:physiology*; D009882:Ophthalmic Nerve / Q000502:physiology*; D018903:Photorefractive Keratectomy / Q000379:methods*; D011446:Prospective Studies