title: [Effects of laser in situ keratomileusis (LASIK) retreatment on the central corneal endothelium and retina and optic nerve].
abstract: OBJECTIVE
  To investigate the effects of laser in situ keratomileusis (LASIK) on the corneal endothelium, retina and optic nerve for correcting residual myopia caused by undercorrection or regression.
  
  
  METHODS
  The pre- and post-operative values of central corneal endothelium and electrophysiological functions of retina and optic nerve were analyzed respectively in 23 eyes of 18 patients who received LASIK retreatment. The endothelium checked by contact specular microscopy was analyzed for central cell density (CCD), coefficient of cell variation in size and hexagonality preoperatively and 1, 4, 12 weeks after the operation. The amplitude and latency of P(100) in standard pattern visual evoked potentials (P-VEPs), that of a, b waves of different reactions in flash electroretinograms (F-ERGs) and also the total amplitude of oscillatory potentials (OPs) were evaluated preoperatively and 2, 12 weeks after the operation.
  
  
  RESULTS
  The mean CCD decreased significantly (3.94%) one week after the operation (P < 0.01). The change was negatively correlated with the thickness of residual untreated posterior cornea (r = -0.719, P < 0.01) and not significantly correlated with the amount of laser pulse (r = 0.371, P > 0.05). There was no significant difference between preoperative and either 4 or 12 week postoperative CCD (P > 0.05). No significant differences in mean coefficient variation and hexagonality were found between preoperative and postoperative values in the follow up (P > 0.05). Examination of electrophysiological function showed that the amplitude of P(100) increased and the latency of P(100) decreased 2 and 12 weeks postoperatively. The significant changes were only at spatial frequency 34' in the P-VEPs test (P < 0.05). In F-ERGs test, there was no significant change in amplitude, latency of a, b waves or total amplitude of OPs between pre-operative and either 2 or 12 week post-operative values (P > 0.05).
  
  
  CONCLUSIONS
  Retreatment after LASIK may cause a reversible reduction of CCD with no morphological changes in a short period (1 week) after the operation. It was not absolutely safe for corneal endothelium when the thickness of residual untreated basal cornea approaches to 200 micro m. These results show that the operation seems not to cause functional impairment in the retina and optic nerve. And it also can improve the quality of vision for some degrees.
authors.affiliation: Department of Ophthalmology, First Affiliated Hospital, Dalian Medical University, China. jane-long@21cn.com
authors.forename: Qin
authors.initials: Q
authors.lastname: Long
authors.forename: Fengju
authors.initials: F
authors.lastname: Zhang
authors.forename: Hongchen
authors.initials: H
authors.lastname: Sun
authors.forename: Ming
authors.initials: M
authors.lastname: Zhou
authors.forename: Bo
authors.initials: B
authors.lastname: Liu
authors.forename: Zhaowen
authors.initials: Z
authors.lastname: Luo
authors.forename: Jun
authors.initials: J
authors.lastname: Zhao
mesh_terms: D000328:Adult; D004728:Endothelium, Corneal / Q000473:pathology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009900:Optic Nerve / Q000503:physiopathology*; D012086:Reoperation; D012160:Retina / Q000166:cytology / Q000503:physiopathology*