Approximately one fifth of the population in the United Kingdom suffers from seasonal allergic conjunctivitis. Symptoms of ocular irritation, redness, and tearing (frequently accompanied by nasal symptoms) typically occur during pollen-producing seasons. As the underlying mechanism of this condition is believed to be a type 1, IgE-mediated hypersensitivity, topical mast cell stabilizers and antihistamines are used to control symptoms. Systemic antihistamines may be prescribed for patients with more widespread symptoms, and steroids are used occasionally in severe cases. Owen and colleagues conducted a systematic review to determine the relative effectiveness of topical mast cell stabilizers and antihistamines in symptomatic therapy for seasonal allergic conjunctivitis.

Electronic databases, including the Cochrane Library, and bibliographies of relevant articles were used to identify clinical trials comparing topical mast cell stabilizers or antihistamines with placebo, and these two classes of agents with one another. Of the 140 original studies identified, 40 met quality criteria for inclusion in the meta-analysis.

Placebo-controlled trials of the mast cell stabilizers sodium cromoglycate, nedocromil, and lodoxamide were identified. The 17 studies of sodium cromoglycate tended to involve small numbers of patients, differed in outcome measures, and showed evidence of publication bias. Nevertheless, the authors calculate a significant difference in perceived benefit over placebo with no important side effects. Patients also perceived significant improvement in symptoms in three of the five trials of topical nedocromil. The authors calculate that patients treated with this drug were 1.8 times more likely to report moderate or complete control of symptoms than patients given the placebo. A significant benefit also was reported for topical lodoxamide compared with placebo, but this was based on one small study. In the pooled analysis of the 12 topical mast cell stabilizer studies, patients were 4.9 times more likely to report symptom relief compared with placebo.

Nine studies comparing topical antihistamines with placebo were identified. Six of these studies used levocabastine, and the remaining studies involved azelastine, emedastine, and antazoline. Most studies used subjective symptom scales completed by patients after provocation, and results showed symptom improvement, especially in itching. A formal meta-analysis was not possible because of study designs.

Eight trials compared the effectiveness of topical mast cell stabilizers with topical antihistamine. A formal meta-analysis was not possible because of differences in the reporting of outcomes. The topical antihistamine appeared to reduce symptoms better than mast cell stabilizers in short-term provocation studies and showed limited evidence of a faster onset of action. Otherwise, no significant differences were apparent between the classes of medication.

The authors conclude that topical mast cell stabilizers and antihistamines provide significantly better symptom relief than placebo in allergic conjunctivitis. Based on available evidence, the choice of a specific agent should be determined by factors such as convenience of use, cost, and patient preferences.