To determine the accuracy of the red reflex test in the detection of anisometropia.

This prospective, single-masked study enrolled new patients younger than the age of 18 years who had not undergone pharmacologic pupillary dilation. A fellow who was masked to all clinical information illuminated both eyes with a direct ophthalmoscope in a darkened room from a distance of 1 m, assessing whether the red reflex between the 2 eyes was symmetric or asymmetric. The patient was then dilated, and cylcoplegic refraction was performed by an attending pediatric ophthalmologist. Exclusion criteria included the presence of strabismus, anisocoria, previous intraocular surgery, media opacity, leukocoria, or nystagmus. Sensitivity was compared with a null hypothesized value of 50% using a 1-sided binomial test.

Ninety-two patients with a mean age of 7.3 years (range 3 months to 16 years) were enrolled. With spherical anisometropia greater than or equal to 0.125 diopters, the sensitivity of the red reflex test was 90.6% and the specificity was 58.3%. With cylindrical anisometropia greater than or equal to 0.25 diopters, the sensitivity of the red reflex test was 81.3% and the specificity was 70%. Anisometropia greater than 1.5 diopters in spherical equivalent (4 patients, range −10.625 to −2.625) or cylinder (3 patients, range 1.75-2.25) was accurately detected by red reflex testing in each case.

The red reflex test can be an accurate screening tool to detect anisometropia when performed by an ophthalmologist.