Reliability of diagnostic tests for contact allergy to mydriatic eyedrops

Adverse reactions due to the administration of mydriatic eyedrops are not uncommon. In Spain, the most commonly used are phenylephrine, tropicamide and cyclopentolate hydrochloride. In this study, 37 patients with adverse reactions to the administration of mydriatic eyedrops were investigated from January 1993 to June 1997. The aim was to assess the reliability of the diagnostic methods used, particularly the adequate concentration of allergens and the introduction of conjunctival challenge as a safe and accurate diagnostic tool in those patients who could not be diagnosed by other methods. Phenylephrine was the drug most frequently causing sensitization (93.5%) among the 31 allergic patients. Preservatives were the cause in only 1. Patch testing detected allergy in 68.5% of the subjects. 2 concentrations (1% and 10%) and vehicles (pet. and aq.) were used for phenylephrine. The most reliable was 10% aq. Reading at D4 was more useful than at D2. The sensitivity of the patch test was low (72.4%) and its negative predictive value (NPV) poor (42%). In 24% of patients, allergy to phenylephrine was detected only by conjunctival challenge test. This diagnostic method is safe and helpful and has not previously been used to diagnose adverse reactions due to mydriatic eyedrops.