Diagnostic ability of barrett's index to detect dysthyroid optic neuropathy using multidetector computed tomography

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% ± 6.06% and 49.44% ± 10.94%in the groups with and without dysthyroid optic neuropathy, respectively (p<0.001). barrett's index sensitivity ranged from 32% to 100%, and barrett's index specificity ranged from 24% to 100%. the best combination of sensitivity and specificity was 79%/72% for bi=60% (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% should be carefully examined and followed for the development of dysthyroid optic neuropathy.