Some long-term wearers of hard contact lenses might be at risk for corneal damage, according to a new study. Researchers at Oregon Health Sciences University's Casey Eye Institute estimate that about 100,000 of the nation's 25 million contact lens wearers risk problems that could lead to vision loss or even a need for a corneal transplant.
Dr. Scott M. MacRae, principal investigator, said that about 10 percent of people who wore hard contact lenses for more than 20 years might be at risk, even if they no longer wear hard lenses."If there is a susceptible population of contact lens wearers, this may represent a significant public health problem," said MacRae, co-director of the Casey Eye Institute Center for Refractive Errors. Other members of the research team are Dr. Mamoru Matsuda of Osaka University Medical School in Japan and David S. Phillips, an epidemiologist in the OHSU department of public health and preventive medicine.
A report on their study of the long-term effects of polymethylmethacrylate lenses, PMMA, commonly known as hard contact lenses, appears in the February issue of Ophthalmology, the journal of the American Academy of Ophthalmology.
PMMA lenses were patented in the United States in 1948. Since then, contact lenses have become the most commonly used medical device in the United States. Remarkably little is known about the long-term effects of contact lenses on the cornea - the protective covering of the front of the eyeball that helps focus light rays on the retina at the back of the eye, MacRae said.
However, the new study shows that some long-term hard lens wearers may have severe changes in endothelial - also called pump - cells lining the undersurface of the cornea, MacRae said. These cells regulate the water content of the cornea, keeping it thin and crystal clear. If damaged, the cornea's endothelial cells are lost - they cannot reproduce themselves.
"What we have learned in 10 years of study is that when you put a contact lens on your eye it is not inert," MacRae said. "It affects corneal health."
Even if they are not having symptoms, anyone who has worn hard lenses for more than 20 years should probably have a thorough eye checkup and perhaps inquire about switching to gas permeable lenses, MacRae said.
Most eye care professionals do not fit hard lenses since they are no longer state of the art, he said. However, "we still have some patients in old hard lenses, and some corneas are surprisingly tolerant to old hard lenses," MacRae added.
Patrick J. Caroline, director of contact lens research at Casey, said rigid gas permeable, RGP, lenses that came along in the 1980s use a type of polymer chemistry that allows more oxygen permeability than even soft contact lenses.
Both MacRae and Caroline strongly recommend RGP lenses or soft lenses over older PMMA lenses.
- Oz Hopkins Koglin
Newhouse News Service