Rare coexistence of disease or pathology Background:Vision loss secondary to optic neuritis is an uncommon adverse effect of nonsteroidal aromatase inhibitors.There have been few reports in the literature on visual disturbance in patients on long-term treatment with Anastrozole for breast cancer prevention; but none had symptoms worse than blurry vision and/or xerostomia. The present patient had acute onset of right-sided vision loss without other neurologic deficits while using the aromatase inhibitor Anastrozole for breast cancer treatment. Case Report:A 69-year-old woman presented to the Emergency Department with approximately 1 month of worsening right eye vision loss that was not associated with any other neurologic deficits or any acute symptoms. The symptom was constant and without alleviating or aggravating factors. After extensive workup with ophthalmologic evaluation, Infectious Disease evaluation, autoimmune tests, brain imaging, lumbar puncture with CSF analysis, and temporal artery biopsy reporting unremarkable results, it was determined that the patient was in an inflammatory state induced by long-term use of Anastrozole, an aromatase inhibitor. Conclusions:The patient's long-term use of Anastrozole likely played a large part in developing right visual disturbance secondary to optic neuritis, as a patient of this age has little risk of developing conditions such as optic neuritis, unilateral loss of vision, and/or autoimmune conditions.