The hyperglycemia of diabetes is toxic to vascular tissues along two scales:
- Macrovascular (atherosclerosis leading to cardiovascular disease)
- Microvascular (retinopathy, nephropathy, and neuropathy, i.e, vision, kidney, and cognition)
Type 1 DM causes damage more quickly and earlier than in Type 2 DM, in which complications can be more insidious and diagnosis delayed.
Vision in diabetics is at risk due to refractive (correctable) errors, cataracts, and glaucoma, all of which are more common in diabetics. Retinopathy, disease progression in the retina, can result in blindness.
Diabetic Retinopathy (DR)
DR is the main cause of impaired vision between the ages of 25-74. The macula, an oval-shaped pigmented area in the central retina responsible for high-resolution and the color vision, can develop edema; the entire retina is at risk of rogue blood vessels hemorrhaging into the retina or detaching it.
Most patient with DR have no symptoms until its latest stages, making screening a priority in preventing it. In Type 1 DM, DR begins within 5 years of their diabetes diagnosis; in Type 2 DM, DR onset can take as long as 20 years.
There are two main forms, based on whether or not there are abnormal new vessels:
- Nonproliferative DR (NPDR): Nerve-fiber infarcts at various layers give a “cotton wool” spottiness to the retina. Retinal hemorrhages, microaneurysms, occluded vessels, and dilated/tortuous vessels appear in the macula and posterior retina. Visual loss, however, is primarily due to macula edema.
- Proliferative DR (PDR): There is neovascularization, along with its complications–vitreous hemorrhage, fibrosis/scarring, and tractional retinal detachment. Neovascularization involves fragile new vessels which rupture, causing hemorrhage within the eye. Visual loss, due to blood blocking the path of light through the eye to the retina, can be temporary until the blood clears, while retinal detachment causes permanent vision loss. PDR can also create a fibrovascular overgrowth that can distort the retina to the point of detachment.