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Smaller flap, nasal hinge reduce LASIK-induced dry eye symptoms
Experts discuss the best strategies to prevent and reduce the amount of neurotrophic dry eye after LASIK.
(Image courtesy of Steven E. Wilson, MD.) |
Smaller corneal flaps were found to reduce the signs of neurotrophic dry eye after LASIK, said Eric D. Donnenfeld, MD.
“The larger the flap, the greater the amount of dry eye,” Dr. Donnenfeld told Ocular Surgery News.
In a study, Dr. Donnenfeld found that patients with 9.5-mm flaps experienced greater dry eye after LASIK than patients who had 8.5-mm flaps. All flaps were created with the Amadeus microkeratome (Advanced Medical Optics, Irvine, Calif.).
“Smaller flaps tend to cause less symptoms because they transect significantly fewer nerve fibers than larger flaps,” Dr. Donnenfeld explained. Transection of nerve fibers can cause LASIK-induced dry eye, a neurotrophic condition that usually takes months to resolve.
With smaller flaps, fewer cornea nerve fibers are harmed, and consequently the risk of neurotrophic dry eye is reduced. The difference in outcomes was statistically significant in Dr. Donnenfeld’s study. However, the disparity was not “astronomical,” he said.
“Most signs and symptoms had resolved by 6 months,” he noted.
Nasal hinge advantageous
“Signs and symptoms of dry eye resolve after 6 to 8 months because that’s how long it takes for the corneal nerve fibers to regenerate, according to confocal microscopy,” said Steven E. Wilson, MD, director of corneal research at the Cole Eye Institute in Cleveland.
Dr. Wilson said that he would not use smaller corneal flaps purely to reduce the chance of neurotrophic dry eye. “Only about 1% to 2% of my patients who do not have pre-existing dry eye develop this problem. If you make a smaller flap, you increase the chance of inducing glare, halo and other long-term, untreatable complications of LASIK,” he said. “So even though it can be a frustrating problem, I rather deal with something that is going to be present for just 6 months rather than a lifetime.”
While flap size might not influence some surgeons to change their LASIK protocol, flap location may.
“Nasally positioned flaps cause less dry eye than superiorly positioned flaps,” Dr. Wilson said. In a study published in Ophthalmology, Dr. Donnenfeld and colleagues found that neurotrophic dry eye symptoms were greater in eyes with superior-hinge flaps and milder in eyes with nasal-hinge flaps. Consequently, corneal sensation was greater in patients who had nasal-hinge flaps. This was statistically significant by P < .001.
“The nerve trunks in the cornea enter nasally and temporally,” Dr. Donnenfeld said. “A superior hinge transects both areas of the cornea where innervation occurs, severing both arms of the neuroplexus.” A nasal hinge transects only one of these nerve trunks, the temporal arm. As a result, more corneal nerves are preserved with the nasal hinge.
Differentiating dry eye
In addition to flap size and location, flap hinge width and depth of flap are also factors that may influence the occurrence of dry eye after LASIK. Investigating the significance of these factors is an area of ophthalmology that requires further study.
“This area of science is obscure to some,” Dr. Wilson said. “A lot has been written about dry eye after LASIK, but I’m not sure that everyone gets it.”
Before surgeons try to treat the condition, they must first understand the cause.
“The definition of general dry eye syndrome and neurotrophic dry eye or LASIK-induced neurotrophic epitheliopathy must be clearly defined and well understood,” Dr. Wilson said.
The most general form of dry eye, aqueous-deficient dry eye, is an inflammatory condition that alters or diminishes tear film or production. This form of dry eye may be caused by a host of internal or environmental factors. Traditional ointments, a short course of steroids or cyclosporine may be effectively used to treat traditional dry eye.
Existing dry eye indications
Neurotrophic dry eye, formally labeled LASIK-induced neurotrophic epitheliopathy (LINE) by scholars, is the corneal condition caused by severed nerves. LINE does not respond to traditional dry eye treatments; symptoms resolve only after nerves have re-grown.
“Time is the only cure. It has to heal itself,” Dr. Wilson said. “In the meantime, it’s frustrating for patients because the irritation commonly falls over the central visual area, causing poor or fluctuating vision until nerve cells grow back.”
While LINE is not a chronic or vision-threatening condition, it often reduces a patient’s quality of vision and quality of life after LASIK. While only 1% to 2% of patients will develop LINE, the risk is much greater for those who have existing dry eye.
“If a patient has dry eye, the incidence of LINE increases to between 20% and 30%,” Dr. Wilson said. Because of the high risk, he often treats dry eye patients with surface ablation instead of LASIK.
“The level of neurotrophic effect is much greater with LASIK than surface ablation because you’re cutting the nerve trunks in the periphery,” Dr. Wilson said. “With surface ablation, you’re just ablating the nerve endings, and they regenerate much faster.”
Patients with existing dry eye who undergo LASIK are pretreated with cyclosporine. “I try to get patients optimized for a few months,” Dr. Wilson said. “But for many, I will perform PRK instead of LASIK because once patients get this condition, though not severe, they really have a tough time with it for 6 to 8 months.”
For Your Information:
- Eric D. Donnenfeld, MD, is a cornea specialist in private practice at Ophthalmic Consultants of Long Island and co-director of the cornea department at Nassau University Medical Center. He can be reached at Ryan Medical Arts Building, Suite 402, 2000 North Village Ave., Rockville Centre, New York 11570; 516-766-2519; fax: 516-766-3714.
- Steven E. Wilson, MD, director of corneal research at the Cleveland Clinic’s Cole Eye Institute can be reached at Cole Eye Institute, 9500 Euclid Ave., I-32, Cleveland, OH 44195; 216-444-5887; fax: 216-445-8475.
References:
- Donnenfeld E., Solomon K, et al. The effect of hinge position on corneal sensation and dry eye after LASIK. Ophthalmology. 2003;110:1023-1030.
- Wilson SE. Laser in situ keratomileusis-induced (presumed) neurotrophic epitheliopathy. Ophthalmology. 2001;108:1082-1087.