UV toxicity may be culprit in post-LASIK dry eye

Hypoesthesia is not the origin of post-LASIK punctuate epithelial keratopathy or the so-calleddry eye syndrome. Rather, these sequelae may represent a phototoxic effect of treatment withthe ultraviolet excimer laser, said Carmen Barraquer-Coll, MD.

"In our surgical and clinical experience we have never seen dry eye in recipients ofpenetrating or lamellar grafts or in eyes that have undergone freezing keratomileusis,epikeratophakia, planar keratomileusis, or in situ keratomileusis with and without a hinge. Norhave we found any publications on the so-called dry eye syndrome after these procedures,"observed Dr. Barraquer-Coll, head, refractive surgery department, Barraquer Clinic, Bogota,Colombia.

"Like LASIK, these are all corneal surgeries associated with nerve sectioning or tissuedenervation," Dr. Barraquer-Coll said. "Use of the excimer laser is the most obvious answer to the question of what is thedifference between LASIK and these corneal surgeries."

Dr. Barraquer-Coll hypothesized that every pulse of the laser produces an equal area ofcollateral damage. In addition, through a reaction with ambient oxygen, there is the potentialfor release of ozone.

This concept is being investigated in a prospective open label clinical trial where eyes wereallocated to undergo LASIK with a standard technique or a protected technique involvingcovering of the limbus, bulbar conjunctiva, and stromal side of the flap. A preliminaryanalysis was performed using data from a total of 143 eyes. The two surgical groups were nearlyequally represented, and they were similar with respect to gender, age, preoperative SchirmerII and tear breakup time results, defocus, and total ablation depth.

In logistic regression analysis, eyes operated on with the protected technique had anapproximately 70% lower risk of dry eye syndrome postoperatively. Females had a threefoldgreater risk than males.