<qa>  What is an inflammation of blood vessels in the retina that can cause retinal damage?This study will look for biological markers of primary retinal vasculitis that can be useful in understanding what causes the disease. It will evaluate its progression, and develop and monitor treatments. Biological markers are substances e.g., chemicals called cytokines and chemokines or antibodies that are associated with a disease or condition such as retinal vasculitis. Retinal vasculitis is an inflammation of blood vessels in the retina that can cause retinal damage and subsequent loss of vision. It can occur by itself primary retinal vasculitis, or it can be part of a systemic vascular disease. 