The incidence of diabetes continues to rise, affecting more than 100 million adults in the United States who are now living with diabetes or pre-diabetes.1 An estimated 34.6 percent of patients with diabetes have diabetic retinopathy (DR), which is the most common cause of vision loss among working adults.2
The development of DR is directly correlated to the duration of the disease as well as comorbidities such as hypertension, hypercholesterolemia, and metabolic control (HbA1c). In this article, we review the stages of DR and discuss the imaging modalities that can be used to diagnose and manage this vision-threatening disease.
Stages of diabetic retinopathy
Diabetic retinopathy is classified as non-proliferative with the absence of neovascularization and proliferative when it is associated with abnormal new blood vessel growth.
Non-proliferative diabetic retinopathy (NPDR) is further divided into mild, moderate, severe, and very severe. Mild NPDR is classified by the presence of microaneurysms. Any additional signs, such as hemorrhages, cotton-wool spots, hard exudates, venous beading, or intraretinal microvascular abnormalities (IRMA) constitute moderate NPDR. Severe NPDR is determined by the “421 rule,” defined as four quadrants of hemorrhages, two quadrants of venous beading, or one quadrant of IRMA. Two of those indicators in any variance designates very severe NPDR.
Proliferative diabetic retinopathy (PDR) is diagnosed by characteristics of neovascularization and further divided into non-high risk or high risk. High-risk characteristics of PDR include neovascularization of the disc (NVD) covering one quarter to one third of the disc area, NVD of less than one quarter of the disc area accompanied by a fresh pre-retinal or vitreous hemorrhage, or NVD of greater than one half of the disc area accompanied by a pre-retinal or vitreous hemorrhage. This stage often requires prompt referral and proper treatment implementation.
Diabetic macular edema
It is important to note that diabetic macular edema (DME) may be observed at any stage of the disease and is the most common cause of visual impairment. Almost 10 percent of patients with diabetes develop macular edema.3
The Early Treatment Diabetic Retinopathy Study (ETDRS) set forth criteria and management for macular edema related to diabetes and recommended treatment with laser for only those cases identified as clinically significant macular edema (CSME).4
CSME is defined as:
• Retinal thickening within 500 µm of the center of the fovea
• Hard exudates within 500 µm of the center of the fovea associated with adjacent retinal thickening
• One disc area of retinal thickening within one disc diameter of the center of the fovea
The advent of new diagnostic modalities, such as optical coherence tomography (OCT), has expanded and redefined DME into center-involving and non-center involving. Center-involving DME is often accompanied by a decrease in visual acuity and subfoveal involvement. Common treatments implicated for the care of DME today include antivascular endothelial growth factor (anti-VEGF) therapies and intravitreal steroids.
Given that both DR and DME may be initially asymptomatic and have the potential to lead to complications as well as visual impairment, it is critical to make the diagnosis early to initiate prompt treatment and proper follow-up. Today’s diagnostic testing aids in both the diagnosis and management of the disease.