Potential new antimicrobial ingredient for multipurpose disinfectant solutions

While most patients do well with contact lenses if they follow their prescribed regimen, there is the risk of bacterial keratitis, an infection of the cornea.

A contaminated contact lens can introduce a number of bacteria into the eye that can be responsible for keratitis, which is relatively easy to treat but can cause permanent vision damage if left untreated. According to the Centers for Disease Control and Prevention, there are nearly 1 million cases of keratitis in the U.S. every year, affecting 3% of contact lens users.  

A study published in the journal Optometry & Vision Science examined the keratitis-fighting effects of a potential new ingredient in multipurpose solutions. Researchers from the School of Optometry and Vision Science at the University of New South Wales in Sydney experimented with using protamine as a disinfecting agent.

Protamine is a naturally occurring combination of two amino acids that are found in the sperm of mammals and fish. The protamine used in this study was taken from salmon sperm.  

Protamine has long been considered safe for humans and is sometimes used to combat unwanted blood-thinning effects of anticlotting drugs. In this study, protamine met the antibacterial and antifungal standards set for multipurpose disinfectant solutions. When protamine was combined with polyhexamethylene biguanide (PHMB) and ethylenediaminetetraacetic acid (EDTA)—two common disinfecting agents found in many commercial multipurpose solutions—the solution performed even better than protamine alone.  

A few reservations

Jeffrey Sonsino, O.D., chair of AOA's Contact Lens and Cornea Section, says the product may be difficult to market given the source of protamine.  

"Researchers are going to have a difficult time separating the public's view of where protamine comes from versus what it does," says Dr. Sonsino. "I don't know how great the public will feel about soaking their contact lenses in a component of salmon sperm."  

What's more, he adds, the key to preventing keratitis has more to do with patient compliance than with the type of multipurpose solution a patient uses.  

"We see a few contact lens complications each week, and 98% of the patients have some sort of poor contact lens hygiene," Dr. Sonsino says. "There is no doubt that if people's hygiene were better, we would probably see one-tenth the complications. It is very rare that someone who follows the guidelines of how to wear, store and care for contact lenses has a complication."  

Ultimately, says Dr. Sonsino, the quest for a better multipurpose solution might be moot.  

"As technology gets better with contact lenses, we are going to move toward more frequently replaced lenses that don't require solutions. We know, beyond a shadow of a doubt, that daily disposables have a better safety profile than frequently replaced lenses."