TO THE EDITOR:

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