9 March 2000


by Kate Melville

For those of us afflicted with poor eyesight, glasses are an everyday fact of life. Unfortunately they can be expensive, break at inopportune time and are a real hassle during sports. So for those who don't want or can't have laser eye correction, the next best thing often seems to be contact lenses.

Well if scientists at Indiana State University are right glasses may be a far safer option. In a recent project they identified that a common bacterium, Pseudomonas aeruginosa that can quickly infect and cause blindness in extended-wear contact lens users. This may not sound too drastic as lenses have to be cleaned, but unfortunately many popular cleaning solutions apparently aren't strong enough to fight Pseudomonas aeruginosa!

Extended wear contact lenses are now used by more than 80% of the 33 million people in the United States who regularly wear contact lenses.

So powerful is Pseudomonas aeruginosa that in cases where the individual already has corneal abrasions or other eye injuries the organism can cause blindness within 36 hours!

According to Thomas Tsai , an optician who worked on the project, "The organism has been observed to initiate an infection of the cornea rather quickly. 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 has been testing the bacteria on a model contact lens and noted the organism's ability to dig into the wall of a lens, making it much harder to kill off using a normal cleaning solutions.

To make matters worse Tsai's team also discovered that some lens solutions actually stick to glass and different types of plastics used in the manufacturing of contact lens cases (making it even harder for the solution to function at an optimum level).

Tsai's tests included 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. Only Alcon's Opti-Free Enhanced significantly reduced the number of organisms on contact.

While US Food and Drug Administration guidelines require 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 to test their solutions," explained Tsai. "We are using samples actually taken from patients who have gone blind as a result of this bacteria."

Suddenly my glasses seem a pretty good bet and my smug contact wearing friends will all soon have something new to worry about!