Is it Acanthamoeba?

by | October 2012


The acute red eye is one of the most common presenting complaints in every comprehensive ophthalmology practice. Most of these cases are relatively benign and self-limited, with occasional exceptions including iritis, episcleritis, epidemic keratoconjunctivitis, or herpes—or the rare angle closure or neovascular glaucoma. Having seen so many red eyes over the years, I almost feel as if I could make the diagnosis from the history alone (perhaps in my sleep). But of course I don’t.

The first question I ask the patient who presents with a red eye is: “Do you wear contact lenses?” The differential diagnosis hangs on the answer. If it is yes, my initial concern is with the cornea, and I look very carefully at the stroma and the epithelium. Even when there is an epithelial defect and stromal inflammatory cell infiltration, the vast majority of these patients respond well to topical fluoroquinolone therapy. Symptoms frequently start to resolve within 24 hours, and within 3 or 4 days the epithelium is repairing itself, the stroma and anterior chamber have fewer inflammatory cells, and the patient almost always feels much better. At that point, the patient and I are happy.

Sometimes the picture is a bit less rosy, but even the more recalcitrant cases typically clear up—they just take longer. But on rare occasions, there is no clinical improvement, even with aggressive antibiotic therapy, and suddenly the diagnostic possibilities take on a more ominous cast. We now have to think about Acanthamoeba, fungal keratitis, or a smoldering herpes outbreak, and the prognosis is much more guarded.

Sometimes the patient is a young contact lens wearer with 20/20 vision, and he or she is now faced with possible corneal scarring and a permanent vision loss. Having lost some time treating a nonexistent bacterial infection, we still want the most rapid diagnosis possible. For this, there is now advanced diagnostic imaging technology that can distinguish amoebic and fungal infection long before cultures (if they are taken at all) come back from the lab.

In this issue, Elmer Y. Tu does an excellent job of describing the science and clinical utility of confocal corneal microscopy. Comprehensive ophthalmology practices like mine may not be able to justify buying a confocal microscope, but virtually all of us have access to referral and academic centers with this technology. It behooves us to refer these recalcitrant infectious keratitis cases as early as possible in the disease process, because prompt, accurate diagnosis and appropriate treatment offer patients the best chance at recovery with minimum vision loss.

While most of us will see just a handful (or less) of the difficult microbial keratitis cases in a year, we may easily see a thousand or more diabetic patients. And, as Tu notes, because confocal microscopy is excellent at imaging corneal nerves it is now being considered as a noninvasive, cost-effective alternative to biopsy for evaluating diabetic peripheral neuropathy. If this comes to pass, ophthalmologists may play a larger role in the treatment of diabetes, and the confocal microscope may find a home in comprehensive ophthalmology practices.

Robert C. Campbell, MD, Editor-in-Chief


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