A 38-year-old man saw a physician for the first time in 10 years after noticing visual loss in his left eye. His history revealed many risk factors for and symptoms of diabetes mellitus (DM). On an undilated funduscopic examination, his physician was able to see some hemorrhages and hard exudates. A fingerstick in the office showed a blood glucose level of 420 mg/dL. He was treated for DM and referred to an ophthalmologist to be evaluated for diabetic retinopathy (Figure 22-1).
Dilated funduscopic photograph demonstrating microaneurysms (small red swellings attached to vessels), which are often the first change in diabetic retinopathy. Also present are flame hemorrhages (black oval) and hard exudates (yellow). Some of the hard exudates are demonstrated with white arrowheads. This case is an example of diabetic nonproliferative retinopathy. (Reproduced with permission from Paul D. Comeau.)
Diabetic retinopathy (DR) is a leading cause of blindness in the United States. Nonproliferative DR is characterized by microaneurysms, macular edema, cotton-wool spots, superficial (flame) or deep (dot-blot) hemorrhages, and exudates. Proliferative DR also has neovascularization of the retina, optic nerve head, or iris. Because patients may be asymptomatic until vision loss occurs, screening is indicated in all diabetic patients. Excellent glycemic control lowers a patient's risk of developing DR.
In developed nations, DR is a common cause of blindness, accounting for 14.4% of blindness in working-age adults.1
In prevalence studies from 33 countries, diabetic retinopathy was present in 27.9% of all patients with known diabetes and 10.5% of patients with newly diagnosed diabetes; prevalence is higher in developing countries.2
In a community-based study, 29% of adults older than age 40 years with DM had DR. Prevalence in black patients was higher than in white patients (38.8% vs. 26.4%).3
Nine years after diabetes diagnosis, 28% of diabetes type 2 patients and 24% diabetes type 1 patients developed diabetic retinopathy.4
ETIOLOGY AND PATHOPHYSIOLOGY
Hyperglycemia results in microvascular complications including retinopathy.
Metabolic and signaling abnormalities found in diabetes and inflammation, in the presence of hyperglycemia, play key roles in the development of DR.5
In nonproliferative retinopathy, microaneurysms weaken vessel walls. Vessels then leak fluid, lipids, and blood resulting in macular edema, exudates, and hemorrhages (Figures 22-1 and 22-2).
Cotton-wool spots result when small vessel occlusion causes focal ischemia to the superficial nerve fiber layer of the retina.
In proliferative retinopathy, new blood vessels form in response to ischemia (Figure 22-3).
Very severe nonproliferative diabetic retinopathy with multiple deep dot-blot hemorrhages, venous beading, and looping. This patient may benefit from panretinal photocoagulation. (Reproduced with permission from Paul D. Comeau.)