Corneal Ectasia After Excimer Laser Keratorefractive Surgery: Histopathology, Ultrastructure, and Pathophysiology

Purpose: To evaluate the histopathology and ultrastructure of corneas developing ectasia after LASIK or photorefractive keratectomy (PRK). Design: Retrospective case series. Participants: Thirteen specimens from 12 patients undergoing corneal transplantation for progressive ectasia after LASIK (12 specimens) or PRK (1 specimen) were obtained for histopathologic and ultrastructural evaluation. Methods: All 13 ectatic corneas were submitted in formalin for light microscopy. Nine specimens were bisected, and the second half was placed in 2.5% glutaraldehyde for transmission electron microscopy (TEM). Main Outcome Measures: Corneal histopathology, ultrastructure, and pathophysiology. Results: Light microscopy of the post-LASIK specimens showed corneal epithelial hypoplasia and occasional foci of epithelial hyperplasia, Bowman's layer breaks, a normal stromal thickness of the LASIK flap, a normal thickness of the hypocellular primitive stromal scar, a thinned residual stromal bed (RSB), and larger than normal artifacteous interlamellar clefts in the RSB of the ectatic region. The post-PRK specimen showed similar findings with the addition of a thinned hypercellular fibrotic stromal scar. TEM showed thinning of the collagen lamellae and loss of lamellar number in the RSB of post-LASIK ectasia corneas or throughout the entire corneal stromal bed in the post-PRK ectasia cornea, with the posterior aspect of the corneal stroma being most affected. Conclusions: Histopathologic and ultrastructural studies suggest that interlamellar and interfibrillar biomechanical slippage occurs when the cornea becomes ectatic after LASIK or PRK in the postoperative stress-bearing regions of the corneal stroma. This 2-phase chronic biomechanical failure process is similar to that seen in keratoconus. Composite sciences classify this chronic biomechanical failure process as interfiber fracture. Financial Disclosure(s): The authors have no proprietary or commercial interest in any materials discussed in this article. Ophthalmology 2008; 115:2181-2191 (C) 2008 by the American Academy of Ophthalmology.