Switch from extended wear to disposable lenses may alter type of corneal ulcers

Issue: September 1997

BySusan Biro

DALLAS — More means less when it comes to the ocular health of the estimated 25 million contact lens wearers in the United States. The more oxygen a lens allows to reach the cornea, the less chance bacteria have to bind to the lens and cause the most serious complication of lens wear today: corneal ulceration.

Pseudomonas is still the leading culprit of central, infectious corneal ulcers, but a shift toward sterile, peripheral corneal infiltrates has some clinicians wondering if the bacterial population has likewise shifted, and if lens wear patterns play a role.

"The ulcer question is important because the number of people who wear lenses is continually increasing. It’s not a static market," said H. Dwight Cavanaugh, MD, PhD. "There may be as many as 20,000 to 30,000 ulcers each year with lens wear, and no one feels this represents an additional, new risk, but simply a rare event multiplied by an increase in a population using a device."

James E. Key II, MD, said the switch from conventional extended-wear lenses to disposable lenses has not eliminated ulceration, but instead "appears to have changed the nature of what we see. We’re seeing more peripheral infiltrates, which in many cases are sterile and not infected, but a reaction to lack of oxygen to the cornea."

Dr. Key, in group practice in Houston, said clinicians still see Pseudomonas ulcers with disposable lens wear, but "they are more rare than what we see with conventional lenses."

The microbial mix

Dr. Cavanaugh said clinicians may be seeing fewer Pseudomonas corneal ulcers for two reasons: a marked decline during the last decade in the use of homemade saline solutions, plus an increase in disposable lenses that are handled less often by wearers. He also said what is missing to confirm this suspicion is published data.

"Somehow the notion is that if you shift from a terrible bacteria such as Pseudomonas to a mere ordinary bacteria such as Staphylococcus you're better off," said Dr. Cavanaugh, vice chair of the department of ophthalmology at the University of Texas Southwestern Medical Center in Dallas. "We'd like to develop a strategy to get rid of ulcers altogether as opposed to shifting which bacteria are causing them."

Oliver D. Schein, MD, at the Wilmer Eye Institute in Baltimore, believes there is a only a perceived shift in which bacteria is causing corneal ulcers, and that this perception has more to do with the way contact lenses are worn today than with the causative organism.

"The severe ulcers we see are still likely to be Pseudomonas however, most of the ulcers seen are minor," Dr. Schein said. "The severe ulcers are rare because the underlying pattern of extended wear use is different. The association of Pseudomonas and corneal ulcers developed in the era of 30-day, extended-wear contact lenses."

Peter C. Donshik, MD, chief, division of ophthalmology, University of Connecticut Health Center, noted an article by Peter R. Laibson, MD, (Laibson P, Cohen E, Rajpal R. Corneal ulcers related to contact lenses. CLAO. 1993;19:73-77) has shown that in the 10 years since disposable soft contact lens were introduced, "the incidence of ulcers may be a little less gram-negative to gram-positive, but we're not really seeing a shift toward Staphylococcus."

In his article, Laibson presented data from the Cornea Service at Wills Eye Hospital that compared corneal ulcers related to contact lens use from 1980 to 1991, and found that: "The numbers of patients with corneal ulcers using disposable lenses was about equal to patients using daily wear and extended-wear lenses."

There are also numerous studies that have documented the incidence of corneal ulcers and infiltrates in a variety of lens modalities, including the causative organism. For example, in a retrospective study published last year (Suchecki J, Ehlers W, Donshik P. Peripheral corneal infiltrates associated with contact lens wear. CLAO 1996;22:41-47) the authors looked at 52 patients with contact lens-associated peripheral corneal infiltrates.

Forty percent of patients wore disposable, extended-wear lenses; 21% wore conventional extended-wear lenses. In their discussion, the authors noted, "In 50% of ulcers cultured, organisms were present. The organisms associated with peripheral corneal infiltrates appear to be less virulent and, thus, have a more benign course with resolution, and rarely affect the visual acuity."

Ulcers vs. infiltrates

Paul C. Ajamian, OD, of Omni Eye Services in Atlanta, said infectious corneal ulcers are rare. In his tertiary care clinic, peripheral corneal infiltrates are more common.

"They are related very much to extended wear, although you can see them in daily wear lenses," said Dr. Ajamian said of the infiltrates. "It’s related to hypoxia, and people present with whitish lesions at the limbus with a mild anterior chamber response. You usually know by looking that it's sterile."

Dr. Ajamian said he normally does not culture peripheral infiltrates and typically treats with an antibiotic for 1 to 2 days, then adds a steroid. "It’s a balance between pretreating it with an antibiotic, then adding a steroid judiciously soon after that and watching it closely."

If he suspects an ulcer is caused by Pseudomonas, Dr. Ajamian will culture it. As part of treatment, Dr. Ajamian will tell a patient with an ulcer or infiltrate who has been wearing contact lenses 2 weeks in a row "to forget about extended wear forever"

Culturing for data

The question, "Is there a shift away from gram-negative to gram-positive ulcers?" could be answered if clinicians cultured all ulcers, said Dr. Cavanaugh. "What we're missing is a good epidemiology study on stratifying ulcers."

The ulcers that tend to occur in the periphery are often said to be culture-negative, he noted, but "when you go back and check the data, you find that an anesthetic drop has been instilled in the eye prior to the culture being taken."

The instillation of preserved anesthetic drops could, Dr. Cavanaugh said, make the culture negative when there are actually organisms present.

"Unfortunately we don’t have the culture data," he said. "We should all culture with nonpreserved anesthetic drops, because if Staphylococcus is there, we'll pick it up."

Future materials and oxygen

In the future, increasing the oxygen transmissibility of contact lenses will be crucial to eliminating ulcers and infiltrates, said Dr. Cavanaugh. "We need a lens you can wear overnight, irrigate in the morning, get some cells off and show that there’s no bacterial binding," he said. "The exciting thing is that there are some lenses in the lab and in clinical trials that may do this."

Brian Levy, OD, director of global biological and clinical research at Bausch & Lomb, Rochester, N.Y., said while researchers do not fully understand the etiology of corneal infiltrates, the thrust of industry is clear and two-fold.

"One is to get more oxygen to the cornea, and the other is to determine the surface which would be more compatible with the ocular environment," Dr. Levy said. "On the rigid gas permeable (RGP) side, industry has been more successful than the soft lens side in oxygen transmission through the material, and RGP chemistry has had some success with surfaces."

The future does hold promise of a soft contact lens that permits more oxygen to reach the cornea, Dr. Levy said, but that in itself may not solve the entire problem of infiltrates.

Dr. Cavanaugh feels that research will result in greater creativity for lens design and eventually allow practitioners to offer patients continuous-wear lenses.

"These new lenses are actually putting in a pinch of materials from rigid lenses, and the current strategy is to develop polymers that are hyperoxygen transmissible but still contain significant amounts of water so they are comfortable and fit like a soft lens," Dr. Cavanaugh said.

For Your Information:

Paul C. Ajamian, OD, may be contacted at Omni Eye Services, 5505 Peachtree Dunwoody Rd., 3rd Floor, Ste. 300, Atlanta, GA 30312; (404) 257-0814; fax: (404) 843-8521; e-mail: ajamian@aol.com.

H. Dwight Cavanaugh, MD, PhD, may be contacted at the Dept. of Ophthalmology, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Blvd., Dallas, TX 75235-9057; (214) 648-8074; fax: (214) 648-9061.

Peter C. Donshik, MD, may be contacted at Eye Physician Associates of Hartford, 29 North Main St., West Hartford, CT 06107; (860) 521-7560; fax: (860) 561-3640.

James E. Key II, MD, may be contacted at Medical Center Ophthalmology, 6624 Fannin, Ste. 2100, Houston, TX 77030; (713) 796-0120; fax: (713) 796-0897.

Brian Levy, OD, may be contacted at Bausch & Lomb, 1400 N. Goodman St., Rochester, NY 14692; (716) 338-5144; fax: (716) 338-0273.

Oliver D. Schein, MD, may be contacted at Wilmer Eye Institute, 116 Wilmer Bldg/Johns Hopkins, 600 North Wolfe St., Baltimore, MD 21287-9019; (410) 955-8179; fax: (410) 614-9651.

None of the doctors has a direct financial interest in any of the products mentioned in this article, nor is anyone a paid consultant for any company mentioned.