RESUMO
OBJECTIVES: The objective of this study was to evaluate the ability of a muscular index (Barrett's Index), calculated with multidetector computed tomography, to detect dysthyroid optic neuropathy in patients with Graves' orbitopathy. METHODS: Thirty-six patients with Graves' orbitopathy were prospectively studied and submitted to neuro-ophthalmic evaluation and multidetector computed tomography scans of the orbits. Orbits were divided into two groups: those with and without dysthyroid optic neuropathy. Barrett's index was calculated as the percentage of the orbit occupied by muscles. Sensitivity and specificity were determined for several index values. RESULTS: Sixty-four orbits (19 with and 45 without dysthyroid optic neuropathy) met the inclusion criteria for the study. The mean Barrett's index values (± SD) were 64.47 percent ± 6.06 percent and 49.44 percent ± 10.94 percentin the groups with and without dysthyroid optic neuropathy, respectively (p<0.001). Barrett's index sensitivity ranged from 32 percent to 100 percent, and Barrett's index specificity ranged from 24 percent to 100 percent. The best combination of sensitivity and specificity was 79 percent/72 percent for BI=60 percent (odds ratio: 9.2). CONCLUSIONS: Barrett's Index is a useful indicator of dysthyroid optic neuropathy and may contribute to early diagnosis and treatment. Patients with a Barrett's index >60 percent should be carefully examined and followed for the development of dysthyroid optic neuropathy.