Posterior Corneal Curvature Changes after Undersurface Ablation of the Flap and In-the-Bed LASIK Retreatment
Presented in part at: American Academy of Ophthalmology Annual Meeting, October, 2004; New Orleans, Louisiana.
Received 31 July 2005; accepted 3 January 2006. published online 19 May 2006.
Objective
To analyze LASIK retreatment-induced changes in the posterior corneal curvature (PCC) with undersurface ablation of the flap (UAF) and in-the-bed techniques.
Design
Nonrandomized, comparative, interventional study.
Participants
Forty-six eyes with a residual spherical equivalent refraction between −0.37 and −2.75 diopters (D) and astigmatism between 0.0 and −1.25 D were included prospectively. In 23 eyes, the calculated postenhancement flap thickness exceeded 150 μm using micropachymetric optical coherence tomography, whereas with further ablation of the bed, the residual bed thickness (RBT) would have been <250 μm, or <55% of the pre-LASIK central pachymetry. In another 23 eyes, RBT allowed the planned ablation for a calculated post-retreatment RBT exceeding 250 μm, >55% of the pre-LASIK central pachymetry.
Intervention
Eyes with insufficient RBT for further ablation underwent UAF retreatment, whereas those with adequate RBT received conventional in-the-bed LASIK retreatment. Examinations were performed before retreatment and 3 and 6 months postoperatively. No eye was lost to follow-up.
Main Outcome Measures
Micropachymetry, Orbscan II scanning-slit PCC data, and visual acuity (VA).
Results
The groups did not differ in age, intraocular pressure, or retreatment ablation depth, but the UAF eyes had a lower mean pre-retreatment RBT (270.7±25.4 μm) than conventional enhancement eyes (353.0±41.5 μm) (P = 0.001). Eyes undergoing UAF had no significant change in PCC, whereas eyes undergoing conventional retreatment had an increase in the posterior corneal power within the central 3-mm zone (P = 0.008) 3 months after retreatment. No significant changes occurred thereafter. The amount of change in posterior corneal power within the 3-mm central zone from before to after retreatment differed significantly between the groups (mean difference, 0.135 D; 95% confidence interval, 0.022–0.248 D; P = 0.02). No keratectasia developed clinically, and no retreated eye lost or gained ≥2 lines of best-corrected VA. Six months after retreatment, the efficacy and safety indices for the UAF procedure were 0.96 and 1.01, respectively, and 1 and 1.06 for conventional LASIK enhancement.
Conclusion
Undersurface ablation of the flap retreatment appears to have less potential for changing the posterior corneal surface than conventional LASIK enhancement and can help reduce the likelihood of retreatment-induced keratectasia.
Department of Ophthalmology, University Clinic, University of Navarra, Pamplona, Spain.
Correspondence to Miguel J. Maldonado, MD, PhD, Department of Ophthalmology, Clínica Universitaria, Av. Pío XII, 36, 31080 Pamplona, Spain.
Manuscript no. 2005-705.
There is a patent pending for the posterior ablation platform, of which Dr Maldonado is the inventor. This instrument, mentioned in the article, was developed by Rhein Medical Inc., Tampa, Florida, in association with Dr Maldonado and is manufactured by Rhein Medical. No other author has any proprietary interest in any product, drug, instrument, or piece of equipment discussed in the article.
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