Purpose: Diagnosing thyroid eye disease–compressive optic neuropathy (TED–CON) is challenging, particularly in cases lacking a relative afferent pupillary defect. Large case series of TED–CON patients and accessible diagnostic tools are lacking in the current literature. This study aims to create a mathematical formula that accurately predicts the presence or absence of CON based on the most salient clinical measures of optic neuropathy. Methods: A retrospective case series compares 108 patients (216 orbits) with either unilateral or bilateral TED–CON and 41 age-matched patients (82 orbits) with noncompressive TED. Utilizing clinical variables assessing optic nerve function and/ or risk of compressive disease, and with the aid of generalized linear regression modeling, the authors create a mathematical formula that weighs the relative contribution of each clinical variable in the overall prediction of CON. Results: Data from 213 orbits in 110 patients derived the formula: y = −0.69 + 2.58 × (afferent pupillary defect) − 0.31 × (summed limitation of ductions) − 0.2 × (mean deviation on Humphrey visual field testing) − 0.02 × (% color plates). This accurately predicted the presence of CON (y > 0) versus non-CON (y < 0) in 82% of cases with 83% sensitivity and 81% specificity. When there was no relative afferent pupillary defect, which was the case in 63% of CON orbits, the formula correctly predicted CON in 78% of orbits with 73% sensitivity and 83% specificity. Conclusions: The authors developed a mathematical formula, the Columbia TED-CON Diagnostic Formula (CTD Formula), that can help guide clinicians in accurately diagnosing TED–CON, particularly in the presence of bilateral disease and when no relative afferent pupillary defect is present.
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