Uveitis refers to inflammation of the uveal tract of the eye: the iris, ciliary body and choroid. A variety of ocular and systemic diseases cause uveitis including collagen vascular diseases, viral and bacterial infections, and autoimmune diseases such as multiple sclerosis. Many cases are "idiopathic"- their cause remains unknown. Uvieits may commonly affect the retina and vitreous and the diagnosis of the cause may be difficult.