The retina is the most metabolically active tissue in the human body per unit weight — consuming more oxygen than the brain cortex. To sustain this, it is supplied by two vascular systems: the retinal circulation (supplying the inner two-thirds) and the choroidal circulation (supplying the outer third including photoreceptors). Diabetic retinopathy attacks the retinal vasculature specifically, through four interconnected pathways.

The earliest structural change is pericyte loss — the loss of the contractile support cells surrounding retinal capillaries. Pericytes regulate capillary tone and maintain the inner blood-retinal barrier (BRB). Their dropout is pathognomonic of DR, visible histologically as "pericyte ghosts." Without pericyte support, capillary walls balloon out to form microaneurysms — the first clinical sign of DR on ophthalmoscopy, appearing as tiny red dots.

As pericyte dropout progresses, the BRB breaks down. Plasma proteins and lipids leak into the retina — forming hard exudates (lipid deposits) and retinal oedema. Capillary occlusion causes focal ischaemia, visible as cotton-wool spots (nerve fibre layer infarcts) and leading eventually to large areas of non-perfusion. The ischaemic retina releases VEGF — vascular endothelial growth factor — in quantities that drive the growth of new, fragile vessels (neovascularisation) that bleed easily into the vitreous and pull on the retina, causing traction detachment.

The Indian diabetic population — already the second largest in the world — is projected to reach 134 million by 2045. Even at the current conservative estimate of 18–28% retinopathy prevalence, that represents 24–38 million people with diabetic retinopathy in India within two decades.

The screening gap is the central problem. India has approximately 18,000 ophthalmologists for a population of 1.4 billion — a ratio of 1 per 77,000 people, compared to WHO's recommended 1 per 50,000 for adequate eye care. Dilated fundus examination requires an ophthalmologist or trained optometrist with indirect ophthalmoscopy equipment. Most tier-3 and tier-4 cities lack consistent access. Telemedicine-based retinal photography — which allows trained graders to remotely assess fundus images captured by non-physicians — is the most promising solution for India's geography, but penetration remains low.

Type 2 diabetes — which accounts for 95% of India's diabetic population — has an insidious onset. Patients are often diabetic for 5–7 years before diagnosis, meaning retinal damage may already be at moderate NPDR stage when the diabetes itself is first detected. The "start from the beginning and screen annually" recommendation assumes a known diabetes onset — which is frequently not the case in India.

The International Clinical Diabetic Retinopathy Disease Severity Scale (ICDR 2003) classifies DR into five levels — no apparent retinopathy, and four progressive stages. Understanding the distinction is essential because the referral urgency, treatment approach, and prognosis differ significantly between stages.

Diabetic macular edema (DME) is the most common cause of visual impairment in diabetic retinopathy — and critically, it can occur at any stage of DR, including mild NPDR. It is not a stage of DR but a complication that can coexist with any level of background retinopathy. This distinction matters clinically: a patient can have mild NPDR (which would normally require only annual review) but concurrent centre-involving DME that requires urgent anti-VEGF treatment.

DME occurs when BRB breakdown allows plasma to accumulate within the layers of the macula — the central 5mm of the retina responsible for all fine detail vision (reading, faces, driving). The OCT cross-section of a macular with DME shows intraretinal fluid pockets, subretinal fluid, and disorganisation of the retinal layers — a picture distinct from the flat, organised architecture of a healthy macula.

Centre-involving DME (CI-DME) — where fluid reaches the fovea itself — is the threshold for anti-VEGF treatment initiation, per NICE, AAO, and the Indian ophthalmology society guidelines. Anti-VEGF (ranibizumab, bevacizumab, aflibercept, faricimab) reduces foveal thickness and improves vision by blocking the permeability effects of VEGF on the BRB. Three or more monthly loading injections are typically required before assessing response.

The national and international consensus on DR screening is consistent and well-established. The challenge is implementation, not guideline — particularly in India.

• Dilated fundus examination (DFE): Gold standard. Ophthalmologist examines the retina through a pharmacologically dilated pupil using direct/indirect ophthalmoscopy or a slit lamp with fundus lens. Requires skilled examiner and mydriatic drops.
• Non-mydriatic retinal photography: A fundus camera captures retinal images without pupil dilation. Images are reviewed by a grader (physician or trained reader). DR telehealth programmes use this model for remote grading — highly scalable in India.
• Fluorescein angiography (FA): Intravenous fluorescein dye is injected and retinal photographs taken as the dye perfuses the vessels. FA maps areas of leakage, non-perfusion, and neovascularisation with high precision — essential for laser treatment planning. FLUROSCÉNE fluorescein strips are used at the slit lamp for anterior segment staining; FA uses intravenous sodium fluorescein separately.
• OCT-Angiography (OCTA): Non-invasive imaging of retinal vasculature without dye injection — detects capillary non-perfusion, microaneurysms, and early NVE at high resolution. Increasingly available in urban Indian centres.
• AI-assisted grading: Deep learning models (Google's EyePACS, Aravind Eye Care's system) achieve sensitivity >90% for referable DR from non-mydriatic photographs — enabling high-volume automated screening at diabetic clinics and telemedicine hubs.

The most powerful treatment for diabetic retinopathy at any stage is optimising the systemic disease driving it. The landmark DCCT trial (Diabetes Control and Complications Trial) demonstrated a 76% reduction in DR risk with intensive glycaemic control in type 1 diabetes. The UKPDS replicated this in type 2. Every 1% reduction in HbA1c reduces DR progression risk by approximately 40%. Blood pressure control (target <130/80 mmHg), lipid management (statins reduce hard exudate formation), and stopping smoking are equally non-negotiable.

The metabolic memory effect — where early excellent control confers lasting protection even if control later worsens — makes intensive glycaemic management in the first 5 years of diabetes the single highest-yield intervention in DR prevention. No laser, no injection, no surgery matches this effect when applied early.

Intravitreal anti-VEGF therapy is now first-line for centre-involving DME and is used as adjunct before panretinal laser in PDR. Available agents in India:

• Bevacizumab (Avastin) — off-label, cheapest option widely used in India; effective but requires compounding from systemic vials; infection risk with improper preparation.
• Ranibizumab (Lucentis/Accentrix) — approved ophthalmic formulation; strong phase III evidence; available in India.
• Aflibercept (Eylea) — VEGF trap with broader binding; superior in patients with very low baseline vision (<69 letters) per DRCR Protocol T.
• Faricimab (Vabysmo) — dual VEGF/Ang-2 inhibitor; extended dosing intervals (up to 16 weeks); most recent approval; reducing injection burden.

Monthly injections for 3–6 months, then PRN (treat-and-extend) protocol. Mean number of injections in first year: 7–9 for bevacizumab/ranibizumab, fewer with faricimab. Vision gain of ≥15 ETDRS letters in 30–40% of patients.

Panretinal photocoagulation (PRP) — applying 1,200–1,800 laser burns to the peripheral retina — destroys ischaemic retina, reducing its VEGF output and causing neovascular regression. It remains the standard of care for high-risk PDR and severe NPDR with high conversion risk. Limitations: permanent peripheral visual field loss, reduced night vision, and inability to reverse existing neovascularisation. Combination with anti-VEGF reduces the number of laser sessions required and may preserve more peripheral field.

Focal/grid macular laser was the standard for DME before anti-VEGF became available — it is still used as adjunct for non-centre-involving DME or to reduce injection frequency in partial anti-VEGF responders.

Pars plana vitrectomy (PPV) is indicated for:

• Dense non-clearing vitreous haemorrhage (typically 1–3 months non-clearing, earlier in monocular patients)
• Traction retinal detachment involving or threatening the macula
• Combined traction-rhegmatogenous detachment
• Refractive dense vitreous haemorrhage preventing laser delivery
• Severe fibrovascular proliferation with epiretinal membrane

During PPV, the vitreous gel is removed, fibrovascular membranes are peeled, endolaser photocoagulation is applied under direct visualisation, and a tamponade agent is used to maintain retinal apposition — either gas (C3F8, SF6) for self-resolving tamponade, or silicone oil for complex detachments requiring longer-duration support. Silicone oil (RETSIL1000 for standard cases, RETSIL5000 for superior retinal breaks and highly mobile membranes) provides stable, clear optical medium allowing post-operative visualisation while the retina reattaches over weeks to months, after which the oil is removed in a second procedure.

Diabetic retinopathy rarely exists in isolation. Diabetes is a systemic disease affecting every organ — the eye is no exception. Three other ocular conditions are substantially more common in diabetics and require simultaneous screening:

• Dry Eye Disease — diabetic keratoneuropathy reduces corneal nerve density, impairing reflex tearing and epithelial healing. Diabetics have significantly higher dry eye prevalence and more severe disease. We covered the full dry eye mechanism and treatment in our Dry Eye Disease: Complete Guide 2026. Screening for DED before laser treatment is clinically important — dry corneas tolerate laser energy less predictably and heal more slowly.
• Cataract — diabetics develop cataracts earlier and progress faster than non-diabetics, through sorbitol accumulation in the lens (the same polyol pathway that drives retinal pericyte dropout). Cataract surgery in diabetics requires careful pre-operative retinal assessment — the surgical trauma can worsen DME. Pre-operative anti-VEGF is frequently given in the month before cataract surgery in patients with concurrent CI-DME.
• Glaucoma — open-angle glaucoma is more common in diabetics (independently of neovascular glaucoma). The shared optic nerve vulnerability in the context of chronically elevated IOP and potential vascular insufficiency makes glaucoma screening essential in every diabetic eye examination. Full coverage in our Glaucoma guide.