Diabetes may in some individuals lead to a serious and potentially blinding eye condition called diabetic retinopathy. Diabetes damages the retina by affecting its blood vessels. 
The vessels weaken which tend to bleed and leak fluid. With disease progression, blood vessels grow along the surface of the retina and typically bleed into the vitreous (the clear gel that fills the eye). Laser, injections into the eye, and sometimes eye surgery are required in some cases to attempt to control the disease.
Diabetic patients should have annual eye examinations, maybe more frequently if disease is present. Tight blood sugar control is recommended to control the progression of diabetic retinopathy.