Increasing risk factors for ectasia after LASIK

Knowledge about the risks factors for corneal ectasia is increasing and some of the risk factors may be very subtle. R. Doyle Stulting, MD, PhD, described how he uncovered some of these factors during Cornea Day 2006 at the American Society of Cataract and Refractive Surgery meeting.

While only about 14 cases of ectasia have been reported in the literature, that number may increase. When Dr. Stulting reported his first cases (10 eyes of 7 patients) after LASIK in 2003, he noted that those that developed ectasia were more myopic than the usual candidates for refractive surgery, had a residual stromal bed that was less than 250 microns thick, and seven of the 10 eyes had forme fruste keratoconus.

These risk factors were validated in a study of patients who underwent successful LASIK, and all three were significant discriminators, he said. Dr. Stulting is professor of ophthalmology, and director, cornea and external disease, Emory Eye Center, Atlanta.

He also evaluated LASIK patients with high myopia and, again, the three factors were confirmed risk factors for ectasia.

Dr. Stulting and colleagues also noticed that ectasia developed in a study in patients with no risk factors. Of 27 eyes, nine met the strict study criteria; the mean patient age was 27.8 years, which is lower than that of a typical LASIK population.

"We found that age is a risk factor without other recognizable risk factors," he stated.

Ectasia also occurs after hyperopic LASIK, he also found. A previous study found that keratoconus can occur after severe eye rubbing. Analysis of other patients indicated that a best spectacle-corrected visual acuity less than 20/20, a family history of premature birth, trauma, and mild retinopathy of prematurity are probable risk factors for the development of ectasia.

He advised that surgeons should not ignore possible "red flags," such as slightly asymmetric topography and increasing astigmatism.

"Are biomechanical properties the missing risk factors? Would some patients develop keratoconus later in life and would some be normal without having undergone LASIK? Is this the explanation for the younger age of the patients who develop ectasia without any risk factors?" he asked.

Increased corneal elasticity may be a risk factor for ectasia, and ways are being developed to measure the elasticity and perhaps differentiate normal corneas from those that might develop ectasia. Finally, he questioned other possible risk factors: whether defective keratocyte metabolism leads to keratoconus and the use of mitomycin C.