Diabetic Retinopathy

Diabetic retinopathy (DR) is a microvascular complication of diabetes mellitus and the leading cause of vision loss among working-age adults.¹ Chronic hyperglycemia damages retinal capillaries, and the resulting ischemia and vascular leakage drive a spectrum of disease from mild background changes to sight-threatening neovascularization.¹

DR is the most common microvascular complication of diabetes, and its likelihood rises with duration of disease and degree of glycemic control.¹ The retina's unusually high oxygen demand and high concentration of polyunsaturated fatty acids make it especially vulnerable to hyperglycemia-driven oxidative stress.⁵ In nonproliferative disease (NPDR), damaged capillaries form microaneurysms that leak fluid and blood into the retina; when that leakage reaches the macula it produces macular edema.¹ As ischemia worsens, the retina releases angiogenic signals driving the neovascularization defining proliferative disease (PDR), which carries a high risk of vitreous hemorrhage and tractional retinal detachment if untreated.¹

Early disease is frequently asymptomatic, which is why routine screening — not symptom-triggered visits — is the standard of care.¹ As disease progresses, patients may report blurred or fluctuating vision (most often from macular edema), floaters from vitreous hemorrhage, or sudden vision loss from advanced complications.¹

Key differentials: hypertensive retinopathy, retinal vein occlusion, radiation retinopathy, ocular ischemic syndrome, and other causes of macular edema (Irvine-Gass syndrome, uveitis, retinitis pigmentosa).³

On dilated fundus exam, NPDR shows microaneurysms, dot-blot hemorrhages, and hard exudates, with venous dilation or beading as severity increases; PDR is defined by neovascularization of the disc or elsewhere.¹ The modified Airlie House / ETDRS classification remains the reference standard for staging severity from stereoscopic fundus photographs.² For macular edema specifically, ETDRS criteria define clinically significant macular edema using thresholds for retinal thickening and hard exudates within defined distances of the macular center — macular edema and proliferative disease are staged independently, so a patient can have severe edema with only mild background retinopathy.³

Historically, focal and scatter laser photocoagulation guided by ETDRS treatment criteria was the mainstay for both macular edema and proliferative disease. That changed with randomized trial data from the Diabetic Retinopathy Clinical Research Network (DRCR.net), which established that intravitreal anti-VEGF therapy (ranibizumab) combined with prompt or deferred laser outperforms laser plus triamcinolone for diabetic macular edema — anti-VEGF agents are now central to first-line management of DME.⁴ Landmark trials worth knowing by name (see the Landmark Trials page): DRCR.net Protocol S showed intravitreal ranibizumab is non-inferior to panretinal photocoagulation for PDR at 2 years, with fewer visual field and vitrectomy complications but a far higher treatment/visit burden (Gross et al., JAMA 2015). The PANORAMA trial showed that proactive aflibercept in eyes with severe NPDR, before macular edema or PDR develop, significantly reduces progression to vision-threatening complications, though whether earlier treatment changes long-term visual outcomes remains debated (Brown et al., JAMA Ophthalmology 2021).

• Screening intervals should be driven by disease stage, not symptoms — many sight-threatening changes are silent until late
• Macular edema and proliferative disease are staged independently; a patient can have severe macular edema with only mild background retinopathy
• Anti-VEGF therapy has shifted first-line management of diabetic macular edema away from laser-only protocols⁴
• Common pitfall: relying on visual acuity alone to gauge severity — acuity can be preserved despite advanced peripheral retinopathy
• Common pitfall: forgetting that pregnancy can accelerate progression, warranting closer surveillance
• Common pitfall: treating "diabetic retinopathy" as a single entity rather than grading NPDR/PDR and macular edema status separately, which changes management