http://www.osnsupersite.com/view.asp?rID=23657

OSN SuperSite Breaking News 9/11/2007

Variations in anterior layers of cornea can affect optic performance

STOCKHOLM, Sweden — The refractive index of the anterior layers of the human cornea is not uniform, leading to variations that can cause corneal light scatter and affect the eye's optical performance, a physician said here.

Sudi Patel, MD, spoke at the European Society of Cataract and Refractive Surgeons meeting about a study he conducted with colleagues that examined the refractive index using the VCH-1 corneal hydrometer. The study included 11 patients who had PRK, LASEK or epi-LASIK and 30 patients who had LASIK. The refractive index was measured after topical anesthesia.

Dr. Patel said they found different measurements for the corneal epithelium, Bowman's layer and stroma, which should be taken into consideration by laser manufacturers and surgeons alike. He said recognizing that there is a difference in individual corneas is important because of the different types of surgery that create refractive changes.

"So much attention is paid to complex optics of the eye that it's a common assumption that the cornea is uniform," Dr. Patel said. "We now believe that if you wish to further improve the optics of refractive surgery, you need to consider the refractive index of the cornea as an individual, not as an average, because of the diversity among subjects."