1. Overview & Epidemiology
Diabetic Retinopathy (DR) is the leading cause of new cases of blindness in adults aged 20–65 years in North America.
Risk Factors: The development and progression of DR are primarily driven by:
Duration of diabetes: The strongest predictor.
Glycemic control (A1C): Better control reduces risk.
Hypertension: Elevated BP accelerates progression.
Dyslipidemia: Associated with hard exudates and vision loss.
2. Pathophysiology & Classification
DR progresses through distinct stages, characterized by damage to the small blood vessels in the retina.
Non-Proliferative Diabetic Retinopathy (NPDR):
Early: Microaneurysms (outpouching of capillaries).
Moderate/Severe: Intraretinal hemorrhages, hard exudates (lipid deposits), cotton wool spots (nerve fiber infarction), and venous beading.
Key Feature: Absence of new blood vessels.
Proliferative Diabetic Retinopathy (PDR):
Key Feature: Neovascularization (growth of new, fragile blood vessels) on the retina or optic disc.
Risk: These vessels bleed easily (vitreous hemorrhage) and cause fibrosis, leading to tractional retinal detachment and severe vision loss.
Diabetic Macular Edema (DME):
Fluid leakage/swelling in the macula (the center of vision).
Can occur at ANY stage (NPDR or PDR) and is the most common cause of visual impairment in people with diabetes.
3. Screening Recommendations
Screening allows for early detection and treatment to prevent blindness. Visual acuity testing alone is insufficient; a comprehensive dilated eye exam is required.
A. Type 1 Diabetes
Start: 5 years after diagnosis (usually not before puberty).
Frequency: Annually.
B. Type 2 Diabetes
Start: At diagnosis.
Frequency: Every 1–2 years. (Interval can be extended to 2 years if there is no retinopathy and glycemic control is stable).
C. Pregnancy (Type 1 or Type 2)
Planning: Screen prior to conception.
During Pregnancy: Screen in the first trimester.
Follow-up: As determined by the eye specialist (DR can progress rapidly during pregnancy).
Note: This does not apply to Gestational Diabetes (GDM), as they are not at increased risk for DR during pregnancy.
4. Prevention & Management
Primary prevention focuses on systemic factors, while secondary treatment targets the eye directly.
Systemic Management (The “ABC”s):
A1C: Optimal glycemic control slows the onset and progression of retinopathy.
Blood Pressure: Control (<130/80 mmHg) is critical.
Cholesterol: Fenofibrate has been shown to slow progression of retinopathy (FIELD and ACCORD-Eye trials), particularly in those with mild-to-moderate NPDR, independent of lipid levels.
Ocular Treatment Options:
Laser Photocoagulation:
Pan-Retinal Photocoagulation (PRP): Used for PDR. Burns the peripheral retina to stop neovascularization.
Focal/Grid Laser: Used for DME (historically the standard, now often second-line).
Intraocular Pharmacotherapy (Injections):
Anti-VEGF Agents (e.g., ranibizumab, aflibercept, bevacizumab): Now first-line therapy for center-involving DME with vision loss. They reduce fluid and improve vision.
Steroids: For resistant cases.
Vitrectomy: Surgery to remove blood (vitreous hemorrhage) or scar tissue (retinal detachment).
5. Diabetes Canada 2018 Clinical Practice Guidelines Recommendations
Key takeaways from the “Recommendations” section (Page S215).
Screening Intervals:
Type 1: Start 5 years after diagnosis, then annually [Grade A, Level 1].
Type 2: Start at diagnosis, then every 1–2 years [Grade A, Level 1].
Screening Method: Assessments should be performed by an experienced professional (optometrist/ophthalmologist) through dilated pupils [Grade D, Consensus].
Pregnancy: Screen women with T1D or T2D pre-conception, in the first trimester, and as needed thereafter [Grade D, Consensus].
DME Treatment: Intraocular anti-VEGF therapy is recommended as first-line for center-involving diabetic macular edema with vision loss [Grade A, Level 1].
Fenofibrate: Fenofibrate (in addition to statins) may be used in patients with Type 2 diabetes to slow the progression of established retinopathy [Grade A, Level 1].