The symptomatic patient with normal phorias at distance and near: what tests detect a binocular vision problem?

Patients often manifest symptoms that appear to be related to binocular distress. Many of these patients have normal heterophoria at distance and near, making the etiology of such symptoms perplexing. We performed a visual examination of patients having normal heterophoria at distance and near in order to investigate which visual analysis tests differentiate symptomatic from asymptomatic patients.

Eighty subjects (30 symptomatic, 50 asymptomatic) with ages between 18 to 35 years of either sex and any race were pooled based on vision-symptom level determined by a 9-question standardized visual-symptoms questionnaire scored using a 100-point scale (asymptomatic: score > or = 85; symptomatic: score < or = 75). Inclusion/exclusion criteria included vision correctable to 6/6 (20/20) Snellen acuity or better in each eye, normal phorias, no latent cyclovertical heterophoria, and normal ocular health.

Of the 30 symptomatic patients, 18 had reduced vergence facility response using 3 pd base-in/12 pd base-out loose prism at distance (n = 10; t-score = 2.41, p < 0.02, d = 76) and near (n = 15; t-score = 3.32, p < 0.01, df = 78) with a significant difference beyond the 0.02 level. No other test including measurement of accommodation, showed a significant between-group difference. However, three patients with normal vergence facility (distance and near) showed a reduced binocular accommodative facility response (+/-2.00 D at 40 cm).

Given a patent with asthenopia, normal phorias, and visual acuity, a differential diagnosis may be made based primarily on using vergence facility and accommodative facility testing. From a clinical standpoint, the results expedite diagnosis of binocular vision abnormalities and direct treatment.