Excess glucose. Excess blood glucose can damage various tissues if persistent exposure is present. The tissues that seem particularly sensitive to excess glucose exposure are kidneys, nerves (esp lower extremities), and eyes. The retina cells are constantly regenerating, but this process is disrupted by persistent excess glucose in the blood that feeds the retina.
Vision loss. Uncontrolled diabetes can lead to a number of problems in the eye including, enlargement of blood vessels, overgrowth of blood vessels, bleeding in the eye, glaucoma and cataracts. All of these changes can lead to permanent vision loss. The key to preventing these changes is to control you blood sugar and to get yearly eye exams which include dilation, exam of the retina and check of eye pressure.