Diabetes is the number one cause of preventable blindness in the developed world. The retina in the back of the eye is the one place in the body where blood vessels can be observed directly. By examining diabetics annually, any leakage of blood vessels caused by diabetes can be detected and monitored so that treatment can be applied when needed.
Background diabetic retinopathy (BDR) is diagnosed when red blood cells and small amounts of protein leak from retinal blood vessels and accumulate in the retina. Normally this has little effect on vision but is an indicator of disease severity and duration. BDR starts after a minimum of 10-12 years of diabetes.
Diabetic macular edema refers to leakage of fluid in the center of the retina, the macula, and does cause blurred vision and distortion. If clinically significant, anti-VEGF treatment or laser treatment is done to help dry up the fluid and reduce leaky vessels. Tighter control of blood sugar and blood pressure helps prevent or improve this condition.
After 25 years of diabetes, about 4% of diabetics, especially the Type I juvenile onset inulin dependent diabetics, progress to the severe, sight-threatening form of retinopathy called PDR.
In Proliferative diabetic retinopathy (PDR), new blood vessels branch out on the retinal surface in an attempt to bring more oxygen. Unfortunately, these vessels are fragile and can bleed into the vitreous cavity, blocking vision and also preventing retinal examination and treatment. Contractile scar tissue forms along with these vessels leading to traction retinal detachment and eventual blindness. Another complication is neovascular glaucoma where scar tissue blocks the outflow of the aqueous fluid that inflates the eye, causing painful high pressure and damage to the optic nerve leading to blindness.
Fortunately, all these grim consequences can be prevented by laser treatment of the peripheral retina called pan-retinal photocoagulation (PRP) applied when these new vessels first appear. If treatment is delayed and the vitreous fills with blood, then treatment becomes much more difficult and costly. Vitrectomy surgery is required to remove the blood, apply laser, release scar tissue and reattach the retina if necessary.