Author’s Disclosure Block: Natalie Chen, none; Heather McDonald, none; Jonathan Micieli, none; Edward Margolin, none

Abstract Body
Purpose: Existing literature regarding optic tract syndrome (OTS), which arises from lesions affecting the optic tract(s), is limited. The Purpose: of this study was to describe the diverse clinical and diagnostic imaging manifestations of OTS in a large series of patients presenting with different etiologies of OTS. Study Design: Retrospective cohort study, with approval obtained from University of Toronto’s Health Sciences Ethics Board. Methods: All patients with OTS seen at two tertiary neuro-ophthalmology practices from 2014 to 2024 were reviewed. Inclusion criteria were: 1) signs associated with OTS (homonymous hemianopia (HH) and/or relative afferent pupillary defect (RAPD) and/or characteristic atrophy of peripapillary retinal nerve fiber layer (ppRNFL) or ganglion cell layer (GCL)); and 2) radiographically confirmed optic tract lesion. Descriptive statistics were used to summarize patient characteristics. Statistical analysis was performed to identify relationships between clinical findings/imaging manifestations and lesion type. Results: Fifty-six patients were identified. The mean age was 49.4 ±16.7 years, and 66% of patients were women. Etiologies included space-occupying lesions (45%), demyelination (20%), ischemia/hemorrhage (16%), non-specific optic tract atrophy (14%), perinatal insult (4%), and trauma (2%). Visual field defects were observed in 98% of patients. Of these patients, 20% demonstrated complete hemianopia while 80% demonstrated incomplete hemianopia, of which 95% were incongruent. Contralateral HH or quadrantanopia was observed in 88% of all patients. Of the 54 patients with peripapillary optical coherence tomography findings, 39% had contralateral band atrophy and ipsilateral hourglass atrophy on ppRNFL. Forty-eight percent of the 46 patients who underwent ganglion cell analysis had homonymous thinning of GCL. Of the 51 patients with available data, 29% had contralateral RAPD. Patients with demyelinating lesions were significantly more likely to present within two weeks of symptom onset (p=0.0180) but were less likely to demonstrate band/hourglass atrophy (p=0.0112) compared to patients with other etiologies. Conclusions: Patients with optic tract syndrome can present heterogeneously, making the condition difficult to diagnose. A high index of suspicion for OTS should be maintained in patients with subtle homonymous defects, especially in the presence of pattern ppRNFL atrophy or homonymous GCL thinning, to ensure timely diagnosis and management.