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A. C. Goncalves, L. N. Silva, E. M. S. Gebrim, M. L. R. Monteiro; Objective Quantification of Orbital Apex Crowding to Detect Dysthyroid Optic Neuropathy Using Multidetector Computed Tomography. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3916.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the ability of area measurements of the orbital apex crowding, calculated with multidetector computed tomography (MDCT), to detect dysthyroid optic neuropathy (DON) in patients with Grave's orbitopathy (GO) and to compare its performance with two previously described categoric methods.
Sixty-five patients with GO were prospectively studied. All patients underwent a complete neuro-ophthalmic examination and were scanned on a MDCT scanner. At the equipment workstation, quantitative measurements of extraocular muscles and the bony area were performed on reformatted coronal sections of the orbits at the planes located at 12mm, 18mm and 24 mm from an interzygomatic line. The ratio between these areas in each coronal scan determined the Orbital Apex Crowding Index (OACI). Orbital apical crowding categoric score as described by Nugent et al. was also performed and the presence of intracranial orbital fat prolapse was recorded as present or absent. Orbits were divided into two groups: those with and without DON. Sensitivity, specificity, positive and negative predictive values were determined for each index and comparisons were made.
Ninety-seven orbits of 53 patients met the inclusion criteria for the study. NOD was diagnosed in 38 orbits of 20 patients and absent in 59 orbits of 33 patients. An OACI 12mm of 0.37 showed sensitivity of 79%, specificity 76.3%, positive and negative predictive values respectively 68.2% and 84.9%. OACI 24mm of 0.68 showed sensitivity of 76.3%, specificity 74.6%, positive and negative predictive values respectively 65.9% and 83.0%. And OACI 18mm of 0.54 showed sensitivity of 84.2%, specificity 78.0%, positive and negative predictive values respectively 71.1% and 88.5%. These results were considerably better than those obtained with the categoric Nugent’s orbital crowding index whose sensitivity ranged from 0.16 to 0.47 with specificity ranging from 0.153 to 1.00. Results were also significantly better than the presence orbital fat prolapse for the detection of DON.
The OACI are useful indicators of DON and may contribute to early diagnosis and treatment. Objectives quantification of the orbital apex crowding appeared to be more accurate than the subjective scoring method based on orbital fat prolapse or subjective orbital apex crowding.
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