Optic Nerve Stretch in Dysthyroid Optic Neuropathy: A Systematic Review and Meta-Analysis

PURPOSE: To review and assess published imaging evidence for optic nerve stretch (ONS) in patients with dysthyroid optic neuropathy (DON), evaluating its prevalence, measurement methods, and potential association with disease pathophysiology. METHODS: PubMed, EMBASE, Cochrane CENTRAL, and ClinicalTrials.gov were searched using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, for computerized tomographic or magnetic resonance imaging studies of ONS in thyroid eye disease. Data were extracted on imaging modality, ONS definition, and association with DON. Pooled proportions were calculated using random-effects models with logit transformation, and heterogeneity assessed with I2. RESULTS: Sixteen studies, comprising 1,277 orbits (508 DON and 769 non-DON), met the inclusion criteria. Five noncomparative studies, mostly earlier papers, report ONS in 43% (0%-100%) of 75 DON orbits. Eleven studies (1,202 orbits) compared orbits with and without DON: 6 studies examined optic nerve contour (317 DON and 435 non-DON) and reported ONS in 66% of DON and 37% of non-DON orbits. Only 2 studies reported ONS as being significantly associated with DON (74% and 64% of orbits), and both reported marked apical crowding (70% and 67%). The pooled ONS proportion was 56% (95% confidence interval: 37%-74%) in orbits with DON and 31% (95% confidence interval: 12%-59%) in non-DON orbits, with high heterogeneity (I2 > 80%). CONCLUSIONS: While optic-nerve stretch is frequently observed in DON, current evidence does not establish it as an independent cause. ONS may reflect geometric changes due to orbital soft-tissue expansion, and the principal mechanism for DON probably remains apical compression and microvascular ischemia of the optic nerve.