title: Changes in the posterior cornea after laser in situ keratomileusis and photorefractive keratectomy.
abstract: OBJECTIVE
  To study the changes in posterior corneal elevation after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) using Scheimpflug topography with the Pentacam anterior segment imaging system (Oculus, Inc.).
  
  
  METHODS
  Department of Ophthalmology, Albany Medical Center, and a private clinical practice, Albany, New York, USA.
  
  
  METHODS
  In this prospective study, 121 consecutive myopic eyes (103 LASIK and 18 PRK) were evaluated preoperatively and postoperatively with the Pentacam to determine elevation changes in the posterior corneal surface. Changes in posterior elevation were calculated by comparing the best-fit sphere preoperatively and postoperatively to a fixed reference sphere using the central 9.0 mm preoperative cornea. Statistical and graphic analyses were performed.
  
  
  RESULTS
  The 103 LASIK eyes had a mean correction of -3.76 diopters (D) and a mean ablation depth of 62.1 microm. The mean estimated residual bed thickness (RBT) (329 microm) demonstrated a mean posterior displacement of 2.64 +/- 4.95 microm. The 18 PRK eyes had a mean correction of -2.69 D and a mean ablation depth of 53.2 microm. The mean estimated RBT (464 microm) had a mean posterior displacement of -0.88 +/- 4.64 microm. The difference in the mean posterior corneal displacement between the LASIK and the PRK eyes was not statistically significant (P>.05, Student t test).
  
  
  CONCLUSIONS
  There was no statistically significant difference in posterior corneal displacement between the LASIK and PRK patients. The changes in PRK and LASIK eyes appeared to be within acceptable measurement variation. Contrary to previous reports, ectatic changes to the posterior corneal surface did not routinely occur after LASIK surgery.
authors.affiliation: Albany Medical College and a private clinical practice, Albany, New York, USA. ciolinoj@georgetown.edu
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Ciolino
authors.forename: Michael W
authors.initials: MW
authors.lastname: Belin
mesh_terms: D003315:Cornea / Q000000981:diagnostic imaging / Q000473:pathology*; D003316:Corneal Diseases / Q000000981:diagnostic imaging / Q000209:etiology*; D019781:Corneal Topography; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000009:adverse effects* / Q000379:methods; D054018:Lasers, Excimer; D009216:Myopia / Q000601:surgery*; D018903:Photorefractive Keratectomy / Q000009:adverse effects* / Q000379:methods; D011183:Postoperative Complications; D011446:Prospective Studies; D014463:Ultrasonography