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

ABSTRACT

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.