PROJECT SUMMARY Pediatric chronic non-infectious uveitis (NIU) is an inflammatory ocular disease that has a substantial risk for sight-threatening complications. Methotrexate (MTX) is the preferred first line systemic treatment for all subtypes of NIU given its overall safety and affordability. However, MTX failure is as high as 50%. Biologic drugs are reserved for those who fail MTX. The long delays waiting for therapeutic effect leads to prolonged glucocorticoid use and continued accrual of ocular damage. As MTX may not be the appropriate first line treatment for all subtypes of NIU, identifying predictors of MTX responsiveness will allow expeditious initiation of biologic therapies. Our long-term goal is to prevent sight-threatening damage in children with NIU by initiating early effective treatment that controls inflammation quickly. This investigation is a longitudinal translational study that is a collaborative effort consisting of experts in rheumatology, ophthalmology, ocular imaging, immunology and biostatistics. The objectives of this study are: 1) To identify baseline demographic, clinical, laboratory, and imaging features in children with NIU that correlate with response to MTX; 2) To assess the value of adding quantitative imaging modalities to monitor response to MTX in children with NIU; and 3) To discover gene expression signatures that predict response and non- response to MTX in children with NIU. A total of 120 children who are starting MTX for NIU will be enrolled in all aims and followed prospectively at 3 and 6 months. Children will undergo serial clinical ophthalmic examinations and imaging by anterior segment optical coherence tomography (AS-OCT), ultrawide field fluorescein angiography (UWFFA), and OCT to assess MTX response. Aim 1 will identify the combination of variables at baseline that predict a patient’s risk of response by 6 months. Aim 2 will assess the use of quantitative imaging to evaluate and monitor MTX response over 6 months. T