Risk Factors and Clinical Evaluation for Corneal Ectasia after LASIK

ABSTRACT

PURPOSE: To describe the clinical evaluation of corneal ectasia after laser in situ keratomileusis (LASIK) and evaluate risk factors. METHODS: Sixteen patients (21 eyes) who had undergone LASIK with corneal ectasia from 1997 to 1999 were reviewed retrospectively. The uncorrected visual acuity, best-corrected visual acuity (BCVA), spherical equivalent (SE), pachymetry, keratometry, intraocular pressure (IOP) and corneal topography were measured before and after LASIK. The targeted residual bed thickness (TRBT) and the ablation percentage of the total corneal thickness were checked. To determine risk factors, we reviewed 60 eyes with uneventful LASIK for 4 years after LASIK. The control group was selected with matched preoperative SE and TRBT similar to the ectasia group. RESULTS: Five (31.3%) of 16 patients developed ectasia bilaterally and the rate of preoperative asymmetric bow-tie pattern was 64.7% in corneal topography. At the final post-LASIK follow-up, disagreement of apices location on anterior and posterior was 33.3% in the right eye and 50.0% in the left eye. The mean time to onset of ectasia was 26.9 15.1 months and 28.6% developed ectasia after more than 40 months after LASIK. In the ectasia group, pachymetry before LASIK, TRBT and pachymetry at postoperative 2 months were thinner than the control group (p<0.05). CONCLUSIONS: Asymmetric bow tie pattern showed a high frequency in the corneal topography of the ectasia group before LASIK and about 1/3 of the cases developed ectasia more than 3 years after LASIK. The incidence of pachymetry before and after LASIK and TRBT was related to the development of ectasia.