Most common cause for rubeosis iridis is

Neovascularization of the iris (NVI) or rubeosis iridis is a peculiar condition that occurs commonly in eyes having proliferative diabetic retinopathy or central retinal vein obstruction. It is characterized by the development of new, branching and enlarged vessels in the iris, the neovascularization being frequently accentuated towards its root and in the angle of the anterior chamber. The new vessels leak protein and give rise to turbid aqueous. NVI may be associated with signs of iritis. Rubeosis iridis, is a medical condition of the iris of the eye in which new abnormal blood vessels (formed by neovascularization) are found on the surface of the iris. Ref.Parson's; 21st edition; Pg. 247