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Background: Differentiating arteritic anterior ischaemic optic neuropathy (A-AION) due to giant cell arteritis (GCA) from non-arteritic anterior ischaemic optic neuropathy (NA-AION) may pose a diagnostic challenge. Our study aimed to assess the use of standard orbital MRI in distinguishing ocular manifestations of GCA from NA-AION., Methods: This study included 25 consecutive patients (11 GCA, 14 NA-AION) who underwent contrast-enhanced orbital MRIs within 3 months of symptom onset. Two radiologists blinded to clinical data independently evaluated MRIs for the enhancement of the optic nerve sheath (ONS) and other orbital structures., Results: On orbital MRI, ONS enhancement of at least one eye was more common in patients with GCA than NA-AION (64% vs 14%, p=0.02). ONS enhancement on MRI was seen in patients with typical ophthalmologic exam findings of A-AION as well as in GCA patients with other features of ocular ischaemia (eg, retinal artery occlusion). Among patients with GCA, ONS enhancement was bilateral in six of seven cases even when visual symptoms and signs were unilateral., Conclusion: Patients with ocular GCA are more likely to have ONS enhancement on MRI compared with NA-AION. ONS enhancement was observed in (i) A-AION and other forms of ocular ischaemia, demonstrating the potential value of MRI in multiple orbital pathologies in GCA, and (ii) both the affected and unaffected eye, suggesting MRI may detect early subclinical ocular disease in GCA. These results highlight the potential value of adding orbital MRI to the diagnostic workup of ocular GCA., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. No commercial re-use. See rights and permissions. Published by BMJ Group.)