Hinge Position in Lasik Flaps Affects Corneal Sensation and Dry Eye
Press Release: American Society of Cataract and Refractive Surgery - May 26, 2003 (San Francisco, CA)
SAN FRANCISCO - Loss of corneal sensation and presence of dry eye signs and symptoms are greater in eyes that have undergone LASIK with a superior-hinged flap - attached at the top of the cornea - than in eyes that have received LASIK with a nasal-hinged flap - attached on the side closest to the nose. This is the conclusion of a study appearing in the May issue of Ophthalmology, the clinical journal of the American Academy of Ophthalmology, the Eye M.D. Association.
In this study, 104 eyes of 52 patients received LASIK in both eyes, one with a superior-hinged flap and the other with a nasal-hinged flap. Corneal sensation and dry eye were evaluated at one week, one month, three months, and six months. Though all eyes experienced reduced corneal sensation and increased dry eye symptoms in the immediate postoperative period, at six months a significant reduction in corneal sensation remained in corneas with superior-hinged flaps. Also, dry eye symptoms were greatest in these eyes.
Lead author of the study, Eric D. Donnenfeld, MD, explained, "The long posterior corneal nerves, which bring sensation to the cornea, enter the eye at the three o'clock and nine o'clock positions. When a superior-hinged flap is cut, both arms of the corneal nerves are cut, whereas with a nasal-hinged flap only one arm is cut. As a result, it takes longer for nerves to regenerate in corneas with superior-hinged flaps."
"This is a good study that persuasively argues the role of hinge position in the occurrence of dry eye after LASIK. In addition to the other factors we know contribute to this problem, Donnenfeld's recommendation for use of nasal-hinged flaps deserves serious consideration," said Academy spokesperson Ernest W. Kornmehl, MD, Associate Clinical Professor of Ophthalmology at Tufts School of Medicine and Director of Kornmehl Laser Eye Associates.
In more recent studies, Dr. Donnenfeld has found that larger flaps and narrower hinges also contribute to loss of corneal sensation and increased dry eye symptoms. "Choosing the correct flap and hinge position and size can minimize the risk of dry eye," he said, but concluded, "Preoperative dry eye is probably the most important factor. A thorough preoperative evaluation by a qualified surgeon is essential in reducing the risk of such complications."