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S. Chang, J.D. Perry; Two–Dimensional Computed Tomographic Analysis for Radiographic Evaluation of Dysthyroid Compressive Optic Neuropathy . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4703.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To evaluate the utility of two–dimensional computed tomographic analysis for evaluation of dysthyroid compressive optic neuropathy. Methods: Retrospective review of consecutive case series. All patients undergoing orbital decompression for dysthyroid compressive optic neuropathy refractory to oral steroid therapy at the Cole Eye Institute between November 1999 and January 2002 were included. Patients underwent high resolution coronal and axial computed tomography. NIH ImageJ software was used to measure the area of intracranial fat prolapse through the superior orbital fissure. The software was also used to measure the ratio of extraocular muscle area to total orbital area in a coronal plane just posterior to the anterior–most projection of the inferior orbital fissure. This was defined as the two–dimensional muscle index. Results: The use of the inferior orbital fissure as a radiographic landmark allowed for reproducible two–dimensional muscle index measurements using the ImageJ software. The area of intracranial fat prolapse was also reproducibly measured using this software. The area of intracranial fat prolapse through the superior orbital fissure was predictive of dysthyroid compressive optic neuropathy. An area > 12 mm2 was found in 24 of 26 (92%) orbits with optic neuropathy. The two–dimensional muscle index was also predictive of optic neuropathy, and a value of > 0.50 was found in 21 of 26 (87%) orbits with optic neuropathy. The level of intracranial fat prolapse and two–dimensional muscle index did not correlate with the degree of optic neuropathy measured by visual acuity, Ishihara color plates, or Humphrey visual field testing. Conclusions: Two–dimensional computed tomographic analysis of intracranial orbital fat prolapse and muscle index predicts the presence of compressive optic neuropathy in patients with dysthyroid orbitopathy.
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