In most cases (97%) neovascular glaucoma is caused by ischemia [5]. The most common underlying diseases are proliferative diabetic retinopathy and proliferative retinopathy after central retinal vein occlusion (CRVO). Rare types of neovascular glaucoma are of non-ischemic nature (e.g., tumor-induced, inflammatory disease) but should be separated because of different treatment strategies (Table 17.1).