Diabetes is a complicated and systemic disease which might bring various impacts to eyes. Diabetes refers to excessive glucose built in body with no sufficient insulin to digest it. Because of the high level of glucose in blood, it could damage the blood vessels and constrict the blood flow to eyes, hence it contribute to the developing of diabetic retinopathy, which is finally leading to secondary glaucoma. At the very beginning of glaucoma, patients don't feel anything abnormal. There is no any discomfort at all. But at later stage, it can cause pain in eyes. If you are diagnosed as diabetes, doctor should recommend you to have detailed examination of eyes frequently to monitor the intraocular pressure status. Glaucoma is the leading cause to blindness. Once it kills the optic nerve endings with this high pressure in eyes, there is no cure to get your vision back. You should take actions as soon as possible.