I applaud Dr. Steven Wilson's important contribution to the November issue on Femtosecond Laser vs. Microkeratome Laser Flaps [p. 58]. It is important that the biology of new technologies be elucidated, and the article includes many seminal observations in that regard.
Among the inclusion criteria that Dr. Wilson utilizes for femtosecond laser flaps are corneas with anterior basement membrane dystrophy. In my referral practice, I have seen a number of patients who have developed late-onset diffuse lamellar keratitis following LASIK in the setting of anterior basement membrane dystrophy. Some of these dystrophic patients did not have a clinical history of recurrent erosions preoperatively, and many did not have intraoperative problems with epithelial adhesion. However, postoperative recurrent erosions, potentially exacerbated by post-LASIK dry eye and/or seemingly minor postoperative epithelial trauma, resulted in intense inflammation of the flap interface. This risk is present whether the flaps are created with a laser or mechanical microkeratome.
It can be argued that the femtosecond laser could have a lower risk of epithelial dysadhesion intraoperatively, and by not disturbing the epithelium or basement membranes, might give more accuracy to wavefront guided treatments than surface ablation, where the intraoperative removal of multilaminar basement membranes could potentially alter the preoperative wavefront signature. However, [in our] ongoing controlled studies … many patients with [ABM] dystrophy have significant changes in wavefront aberrations over time. This may reflect the dynamic cycle of redeposition and enzymatic removal of the duplicated basement membranes and cellular and amorphous debris by matrix metalloproteinases. Upregulation of these zinc-containing degradative enzymes may induce cytokine activation, cleavage of cell adhesion molecules and the creation of biologically active fragments, contributing to the development of diffuse lamellar keratitis post-LASIK. Elevated matrix metalloproteinase (MMP-2 and -9) levels have been observed in the tear fluid of patients with recurrent corneal erosions.
These findings suggest that patients with [ABM] dystrophy may best be treated with advanced surface ablation or PRK, rather than LASIK with either the femtosecond or mechanical microkeratome, given the inherent postop risks discussed. I encourage Dr. Wilson to continue his groundbreaking studies on the biology of corneal refractive surgery.
Jay S. Pepose, MD, PhD
St. Louis