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UI study shows correlation between amoeba levels, onset of eye problems

IOWA CITY, Iowa -- There are pesky, microscopic organisms lurking in lakes and ponds, just waiting for unsuspecting individuals on which to latch. As a result, it should come as no surprise that a University of Iowa study showed the higher the concentration of amoebas in surface water, the more likely one might be to develop an eye infection.

However, the correlation does not necessarily mean that the individuals will catch the infection by coming into contact with contaminated water. Only 17 percent of the UI study patients noted exposure to such water. The precise link between the amoeba levels in surface water and the onset of amoeba infections remains obscure.

"We have a lot of questions about this that need to be answered," said Dr. William Mathers, UI professor of ophthalmology and principal investigator of the study. "But these findings strengthen our understanding of the relationship between our environment and amoeba-like disease."

From January 1993 through December 1996, UI researchers diagnosed 137 cases of amoeba-like keratitis, or inflammation of the cornea, in Iowa. Over the four years, the researchers found the onset of infection symptoms varied significantly from month to month. The infections peaked in June with an average of 4.25 cases and November when the average reached five cases. These times closely correspond to the periods each year when amoeba levels in surface water are highest. The lowest infection rate occurred in February with a reported average of 0.75 cases.

Mathers said researchers do not know why amoebas on the eye result in frequent infections. Amoebas are found elsewhere on the human body and do not cause problems.

Of the 137 diagnosed cases, 52 patients (39 percent) reported contact lens use. Mathers speculated that the large number might be due to the fact that contact lens wearers touch their eyes more frequently and, thus, are more likely to contaminate their eyes. Mathers estimates that one in 10,000 contact lens wearers has an amoeba-like infection each year.

Most of the eye infections are minor -- not blinding, but bothersome. Patients complain of discomfort, irritation or blurred vision. Very few individuals end up with vision loss or scarring, but it is possible if left untreated, Mathers said. Treatment usually involves the use of special eye drops that patients take for at least several months.

Mathers' research into amoeba-like eye problems is included in the October issue of the British Journal of Ophthalmology. He and other UI researchers plan to continue to investigate amoebas and how they affect the eye.

"This research is important," Mathers said. "It is a significant public health issue. Amoeba-like infections are treatable problems, and better detection will result in improved eye health."

Until recently, researchers did not know the extent to which amoebas infected the eye. Most had attributed patients' complaints to bacterial infections. Prior to 1993 UI ophthalmologists diagnosed only about two cases of amoeba-caused infections annually. It was not because they were not occurring, but because there was no real way to detect them. For the past five years, UI researchers have used a confocal microscope to identify amoebas. As a result, researchers have been able to diagnose many more types of previously unknown amoeba infections. Now UI researchers confirm 50 amoeba problems each year, placing the pathogen as one of the most common causes for eye infections.

Mathers became interested in the water amoeba-eye infection correlation following the great Midwestern floods of 1993. It was then that he began noticing problems in patients from counties with the highest levels of ground water contamination. Through those patients and the confocal microscope, UI ophthalmologists learned what to look for in amoeba eye infections.

Individuals can take precautionary measures to guard against infection. Mathers recommends that contact lens users wear and clean contacts as directed and that everyone practice good eye care.