Most common cause of rubeosis iridis: (A) Tumor, (B) CRAO, (C) Radiation retinopathy, (D) Diabetic retinopathy
Answer is D. it develops following retinal ischemia which is a common feature of:
●proliferative diabetic retinopathy 
●central retinal vein occlusion 
●sickle cell retinopathy 
●Eale's disease