Hess Screen Test Distinguishes Decompensated Esophoria From Esotropia Due To Sagging Eye Syndrome.

PURPOSE: To determine whether comparison of Hess screen test (HST) measure of esodeviation with the prism cover test (PCT) can distinguish decompensated esophoria (DE) from sagging eye syndrome (SES). DESIGN: Retrospective, comparative cross-sectional and clinical cohort study. METHODS: Patients with acquired esotropia due to DE or SES were included. Primary outcome was the difference in central gaze esotropia measured with the HST versus the PCT at distance and near. The diagnostic value of the HST-PCT discrepancy was evaluated by Bayesian posterior probability for distinguishing DE from SES, and postoperative HST-PCT discrepancy was evaluated as a predictor of necessity of reoperation. RESULTS: A total of 140 patients were included, 54 with DE, 86 with SES. Esotropia by HST at 24.6 ± 11.8Δ (standard deviation) in DE significantly exceeded that by PCT at distance of 18.4 ± 9.9Δ Δ (p < 0.0001), whereas HST and PCT measurements of esotropia were nearly identical in SES 12.2 vs. 11.9Δ, respectively (p = 0.61). An HST-PCT discrepancy of at least 10Δ yielded a posterior probability of DE of 91%. Patients operated for DE who continued to exhibit HST-PCT discrepancy of at least 10Δ had 80% rate of reoperation, compared with 14% in patients with less discrepancy (p = 0.008). CONCLUSIONS: The HST unmasks a systematically larger esodeviation than the PCT in DE but not SES, consistent with their differing pathophysiologic mechanisms: DE is a central vergence disorder, distinct from connective tissue degeneration in SES.