Organism Can Cause Blindness In Extended-Wear Contact Lens Users If Left Untreated

More than 33 million people in the United States wear contact lenses, according to 1998 figures from the Vision Council of America. Of those, more than 83 percent use soft (including extended wear) contacts.

It is this population of contact lens wearers that is at risk of coming in contact with the organism Pseudomonas aeruginosa. This common bacterium can cause blindness within 36 hours in cases where the individual already has corneal abrasions or other eye injuries.

"The organism has been observed to initiate an infection of the cornea rather quickly," said Thomas Tsai, an optician and a senior life sciences and chemistry major at ISU. "It can double in number in less than an hour (from 1,000 to 2,000 cells), cause vision impairment within a few hours and total blindness within 36 hours when left untreated."

Tsai and Dr. Kathleen Dannelly, assistant professor of life sciences, are currently testing the bacteria on a model contact lens and have noticed the organism's ability to burrow into the wall of a lens, making it harder to kill with recommended cleaning solutions. As a result, they are looking into the possibility of a vaccine to prevent infection from ever occurring.

"Eye infections due to this strain of Pseudomonas were very rare before contact lenses became popular," Tsai explained. "The use of extended wear lenses, in particular, has caused it to become even more common."

The scientists also recently discovered that different lens solutions adhere to glass and different types of plastics commonly used in the manufacturing of contact lens cases. This, too, can interfere with a solution's ability to function at optimum levels, according to Tsai.

Tsai and Dannelly have been studying the effects of five contact lens solutions against two strains of Pseudomonas aeruginosa. Included in the testing were solutions by leading manufacturers, including Bausch and Lomb's new ReNu formula, Alcon's Opti-Free Enhanced, Original Opti-Free and Opti-One and Allergan's Complete.

Current Food and Drug Administration (FDA) guidelines require that contact lens solutions kill bacteria three times over in order to be deemed effective.

"The FDA uses a common and weaker form of this bacteria (found in soil) to test their solutions," explained Tsai. "We are using samples actually taken from patients who have gone blind as a result of this bacteria."

Dannelly and Tsai first tested the solutions' effects on the Pseudomonas sample in a dish, without applying the organism to an actual contact lens.

The ReNu formula (Bausch and Lomb) was found not to have much effect on the Pseudomonas even after eight hours in the solution; however, Alcon's Opti-Free Enhanced significantly reduced the number of organisms on contact.

"I would like to see doctors and opticians explain the cleaning regimen better. Patients also should clean their lenses thoroughly and contact their doctor as soon as they notice any severe irritation or redness. But, most importantly, people should never sleep with contact lenses in," Tsai said.

Tsai said he became interested in studying Pseudomonas infections with contact lens use as an optician at Wal-Mart. Dannelly, Tsai's co-investigator, was already studying Pseudomonas and its effects on the lacrimal gland (which causes tears), so it seemed a perfect fit to join the two areas of interest together, Tsai explained.

Tsai and Dannelly are working to secure grants through Wal-Mart and the National Institutes of Health to support their research.