Prognostic factors for acanthamoeba keratitis

New guidelines have emerged to help predict post-infection visual outcomes

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Source for all: Francis Mah, M.D.

The stage at which you catch an acanthamoeba keratitis infection can be highly predictive of the ultimate outcomes, according to results of a recent study published in the November 2008 issue of Ophthalmology. While the numbers are a bit murky, some have estimated that this infection may affect about one in 10,000 contact lens wearers, said Elmer Y. Tu., M.D., director of the cornea and external disease service, University of Illinois Eye and Ear Infirmary, Chicago.

Sifting through non-specific signs

One of the difficulties with this condition is that the hallmarks can be quite varied. Cases that are often used for classic teaching are those found late in the disease process. “In these cases, patients had horrible pain, very poor vision, and their eyes were horribly inflamed,” Dr. Tu said. “Earlier stages, however, are actually quite non-specific. The symptoms can be as mild as some irritation or just an irregularity of the epithelium on the surface of the eye.”
To help practitioners better determine how their patients will likely fare with the disease, investigators here decided to launch the retrospective case control study of 65 acanthamoeba keratitis patients. “Because it is such a rare infection, doctors haven’t had the ability to identify what the positive and negative prognostic factors are for these patients when they walk into their office,” Dr. Tu said. “Since we had a reasonable number of patients, especially in comparison to some of the larger studies, we wanted to look at the characteristics of these patients to see if we could predict which would do well and which would do poorly.”
As a rule, most patients do well with treatment, but there has been no way to identify those who may not respond as readily. “When we look at our results we see that a majority of the patients are actually doing quite well after they are finished with their treatment,” Dr. Tu said. “But there is still this subset of patients who have significant loss of vision, and we wanted to figure out how early we could identify those patients.” The hope was that perhaps these patients could then receive a different type of intervention.

Surprising visual predictor

The fact is when investigators looked at outcomes with acanthamoeba they found that the majority of patients did quite well. When they looked at prognostic factors, they were surprised to find that old thinking did not necessarily hold here. “One of the things that doctors had suggested in the past as a prognostic factor was the length of time that a patient had an infection or symptoms correlates with the ultimate result or outcome,” Dr. Tu said. “What we found in this study is that that isn’t true. Although the amount of time that patients describe symptoms is loosely related to the stage or depth of their disease when they present, it didn’t correlate with their ultimate visual outcome.”
However, one strong prognostic factor that was identified was the stage at which the patient presented for treatment strongly correlated with visual outcome. Those with deep infections fared much more poorly than their counterparts with superficial disease. Basically if patients come into your office with superficial disease or superficial disease with some inflammation of their nerve, those patients have a 10 times greater likelihood of doing well, meaning vision of 20/25 or better, than those patients who present with disease that’s deeper in the cornea, that’s infiltrating either a stoma or causing an immune reaction, Dr. Tu said.
While there are still challenges in recognizing and treating this particular infection, from a prognostic standpoint the clinical picture has improved. “Once it is recognized, you have a reasonable comfort level in describing to patients what their prognosis is,” Dr. Tu said. “If they present with an early stage of disease, the prognosis for preserving good vision at the end is actually quite good.” For those with a deeper level of disease, the study offers some guide posts as well. “The take-home message from a clinical standpoint is that if they do present with a deeper level of disease, those patients need to be watched more carefully,” Dr. Tu said. “They may need more aggressive treatment, including oral medications, that aren’t normally used in the treatment of acanthamoeba keratitis. There’s also the possibility of needing a corneal transplant at an earlier stage rather than waiting for them to deteriorate further.”
Overall, Dr. Tu hopes that practitioners will continue to watch for acanthamoeba keratitis. “I want to make people aware that acanthamoeba keratitis appears to be continuing,” he said. “It’s something that everyone should remain vigilant about because it is still occurring at a rate much higher than historically we would have expected.” Armed with these new study results, he hopes that practitioners can be better prepared to combat the condition. “Hopefully this paper will give doctors a bit more direction on how to best manage and counsel these patients when they come in,” he said. “It can be quite a frightening diagnosis, especially when patients go on the Internet and start reading some of the horror stories of what can occur.”

Editors’ note: Dr. Tu has no financial interests related to his comments.

Contact information

Tu: 847-571-3966, etu@uic.edu