Update on allergic conjunctivitis offers differing views

Allergic conjunctivitis remains a common, albeit unglamorous clinical problem. Our state and local ophthalmologic societies do not commonly invite speakers to update us on the latest innovations in allergic conjunctivitis, and rarely do symposia devoted to this topic at the annual meeting of the American Academy of Ophthalmology fill to overflowing.

Nonetheless, as another springtime blooms, we will likely see a substantial number of patients presenting in our offices with the signs and symptoms of allergic conjunctivitis. Compared with 20 years ago, when therapy was basically limited to cool compresses and antihistamines, we are now fortunate to have a number of effective topical therapies that interrupt the cells and cytokines responsible for pruritus, erythema, chemosis, and symptoms.

Which of the various therapeutic options are most effective for this condition? This issue of Ophthalmology Times includes several updates relative to allergic conjunctivitis, including two reports on the relative efficacies of two therapeutic agents, epinastine HCl ophthalmic solution 0.05% (Elestat, Allergan) and olopatadine HCl ophthalmic solution 0.1% (Patanol, Alcon Laboratories).

What is the reader of Ophthalmology Times to do in the face of conflicting data from authorities in the field? Does the presence of conflicting data mean that one study was fatally flawed, or that one set of data were somehow manipulated?

When the findings from two studies disagree, we physicians need to keep a number of facts in mind. First, it is actually fairly common for results to vary among different studies. Differences in experimental methods, subject inclusion and exclusion criteria, dosing regimens, etc. may sometimes seem minor, but they definitely can influence study outcomes. Are allergens and patient populations, for example, different in New York from those in Southern California?

Similarly, the pharmacology can be complex. In one instance, carefully performed laboratory studies have shown that a certain polypeptide promotes blood vessel growth, while other studies report that the same polypeptide inhibits vessel growth. The discrepancy has been found to relate to the different concentrations of polypeptide in the two studies, or to other differences in the experimental setup.

One study was not "right" and the other "wrong"; instead the findings in complex biological systems are influenced by a number of factors, some known and others unknown.

One experimental setup may more closely mimic the "real" clinical setting, but which one that is may not be immediately apparent.

How do we deal with this uncertainty? We can look at multiple studies, instead of acting upon a single, unconfirmed report. Does the preponderance of studies point to a single agent that seems more effective and less toxic? We can also look at outcomes in our own practices, and query colleagues about their experiences. With rare conditions we may be more dependent upon guidance from experts, because we may not have enough of a sample size in our own practices to allow us to draw conclusions.

So sometimes we need to be critical and skeptical readers, learning from but not entirely relying upon what we read in publications or hear in our continuing medical education meetings.

Sometimes we have to look carefully at the results we are getting in our own patients, and decide for ourselves how best to choose from amongst a wide variety of therapies.

Sometimes we actually have to fall back on the scientific method we learned in medical school and figure out what works best for our patients.

Sometimes we don't have a cookbook to guide how we treat all patients, and that's one reason that being a physician is still so much fun and so intellectually rewarding.

Peter J. McDonnell, MD is director of The Wilmer Eye Institute, The Johns Hopkins University School of Medicine, Baltimore, and chief medical editor of Ophthalmology Times. He can be reached at 727 Maumenee Building, 600 North Wolfe St., Baltimore, MD 21287-9278. Phone: 443/287-1511 Fax: 443/287-1514 E-mail: pmcdonn1@jhmi.edu