title: Prospective evaluation of factors associated with post-LASIK corneal birefringence with scanning laser polarimetry.
abstract: OBJECTIVE
  To identify factors that affect corneal birefringence, such as the corneal polarization axis (CPA) and corneal polarization magnitude (CPM), after laser in situ keratomileusis (LASIK) using scanning laser polarimetry with a variable corneal polarization compensator.
  
  
  METHODS
  The CPA and CPM from 42 patients (42 eyes) who underwent LASIK and 24 normal untreated subjects (24 eyes) were measured 1 week before and 1 week after LASIK. Changes in the CPA and CPM after LASIK were studied using Student t test and Pearson correlation coefficient.
  
  
  RESULTS
  In the LASIK group, the post-LASIK CPA and CPM significantly changed, whereas both values did not change in normal subjects. Among 5 candidate factors [preoperative CPA (pre-CPA), preoperative CPM (pre-CPM), age, change in corneal curvature, and ablation depth], the change in CPA was significantly correlated with the pre-CPA (r=-0.793) and pre-CPM (r=0.339). The change in CPM was correlated with the pre-CPA (r=-0.455) and pre-CPM (r=-0.411). Over 83% case of postoperative corneal birefringence can be explained by only 2 parameters with regression analysis.
  
  
  CONCLUSIONS
  The pre-CPA and pre-CPM are strongly associated with LASIK-induced changes in CPA and CPM. Variations in age, changes in corneal curvature, and ablation depth do not contribute to changes in either parameter.
authors.affiliation: Sensho-kai Eye Institute, Kyoto, Japan. t-shoji@yg7.so-net.ne.jp
authors.forename: Takuhei
authors.initials: T
authors.lastname: Shoji
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Takahashi
authors.forename: Masami
authors.initials: M
authors.lastname: Park
authors.forename: Kazusiro
authors.initials: K
authors.lastname: Okazaki
authors.forename: Masaki
authors.initials: M
authors.lastname: Tanito
authors.forename: Etsuo
authors.initials: E
authors.lastname: Chihara
mesh_terms: D000293:Adolescent; D000328:Adult; D001718:Birefringence; D003315:Cornea / Q000502:physiology*; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D007834:Lasers; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000601:surgery; D009412:Nerve Fibers / Q000473:pathology; D009898:Optic Disk / Q000473:pathology; D009901:Optic Nerve Diseases / Q000175:diagnosis; D011184:Postoperative Period; D011446:Prospective Studies; D012165:Retinal Ganglion Cells / Q000473:pathology