Risk Factors and Clinical Evaluation for Corneal Ectasia after LASIK

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.

Change of Posterior Corneal Surface after Laser In Situ Keratomileusis; One Year Fallow-up

PURPOSE: To investigate the change of the posterior corneal surface for 1 year after LASIK METHODS: Ninety-nine eyes of 57 patients who underwent LASIK were evaluated retrospectively. The posterior corneal surface was evaluated before surgery and at 1 week, 2 months, 6 months and 1 year postoperatively. The patients were divided into two groups based on the preoperative mean spherical equivalent (Group I; -2.5 ~ -6.0 D, Group II; -6 ~ -10 D) and two groups based on the residual bed thickness (RBT: Group A; 250 ~ 300 micrometer, Group B; 300 ~ 350 micrometer). We also grouped them based on the ablation percentage of the total corneal thickness (P/TCT: Group 1; below 10%, Group 2; 10-15%, Group 3; 15-20%) RESULTS: The posterior corneal surface in Group I was shifted forward 14.19 +/- 8.98 micrometer at 1 week, 7.93 +/- 5.64 micrometer at 1 year after LASIK, and 19.77 +/- 6.97 micrometer and 14.93 +/- 6.95 micrometer in Group II, respectively. It was displayed forward shift 19.48 +/- 8.54 micrometer at 1 week and 13.04 +/- 7.14 micrometer at 1 year in Group A and 11.64 +/- 6.09 micrometer and 7.07 +/- 5.26 micrometer in Group B, respectively. The values at the same times were 8.49 +/- 5.83 micrometer and 5.45 +/- 4.18 micrometer in Group 1, 17.21 +/- 7.73 micrometer and 9.12 +/- 5.26 micrometer in Group 2 and 20.25 +/- 8.16 micrometer and 16.05 +/- 7.24 micrometer in Group 3, respectively. CONCLUSIONS: The posterior corneal surface shifted forward early time after LASIK, but showed a trend toward gradual backward shifted over time. The eyes with higher myopia, thinner RBT and higher P/TCT were more shifted forward the posterior corneal surface at l year after LASIK.