Contact Lens Cultures Provide Eye Infection Clue

MELBOURNE, Australia, Sept. 11 -- Cultures taken from contact lenses can be a useful clinical aid in cases of microbial keratitis, researchers here said.

In a retrospective analysis, bacterial cultures obtained from contact lenses were significantly (P<0.001) likely to be the same as those found in the corneal scrapings, according to Sujata Das, M.S., F.R.C.S., of the University of Melbourne, and colleagues.

The finding "highlights the fact that contact lens culture may help in identification of the causative organism in many cases of contact lens-related microbial keratitis," Dr. Das and colleagues said in the September issue of Archives of Ophthalmology.

But they added that contact lens cultures -- while useful -- should not replace the gold standard of corneal scraping cultures as way of determining the cause of infection, they wrote.

"Contact lens culture helps in providing some vital clues," the researchers said, "especially in the situation in which corneal scraping results are negative and the patient is already taking a broad-spectrum antibiotic at the initial visit. However, these results should be interpreted with caution, keeping common contaminants in mind."

The researchers analyzed records of corneal and contact lens cultures from 49 patients between Jan. 1, 2001, and Dec. 31, 2004 at Royal Victorian Eye and Ear Hospital.

All told, there were 50 corneal specimens, because one patient had both eyes involved.

The study found that 17 corneal scrapings (34%) yielded bacterial cultures, compared with 35 contact lenses (70%).

Of the 17 positive corneal scrapings, 13 (76%) yielded organisms that were identical to the ones grown in their contact lens cultures. The association was significant at P<0.001, the researchers said.

In two eyes, different organisms were isolated from the corneal scrapings and the contact lenses, and for the remaining two eyes, the lenses did not yield a positive culture.

In 11 eyes, ulceration was restricted to the peripheral cornea and corneal scrapings were culture positive in only one of those cases.

In the remaining 39 eyes, infiltrate was localized to the central cornea or to the midperipheral to peripheral cornea. In those cases, corneal scrapings were culture-positive in 16 of 39.

In 27 patients, the contact lenses from both eyes were sent to be cultured and in 21of them, the organisms found on the lenses were identical, Dr. Das and colleagues reported.

The most common organism found was Serratia marcescens, identified in nine corneal scrapings and on 19 contact lenses.

Next was Pseudomonas aeruginosa, found in four eyes and four contact lenses, although most studies report it to be the most common pathogen involved in contact lens-related corneal infections, Dr. Das and colleagues said.