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OP9.2 | Diabetic Retinopathy — SDL Guide (Part 2)

Ocular Examination and Investigation in Diabetic Retinopathy

A systematic examination approach is essential because diabetic retinopathy has a wide geographical distribution across the fundus, and early lesions near the macula can be missed by an unsystematic scan. The examination strategy combines clinical tools with imaging modalities that provide information beyond what the naked eye can see through the ophthalmoscope.

Best corrected visual acuity (BCVA): measured first in all diabetic patients. Reduced acuity suggests macular involvement (CSME) or advanced PDR. Normal acuity does not exclude significant retinopathy.

Dilated fundoscopy: the cornerstone of DR examination. Pupils must be pharmacologically dilated (tropicamide 1%). Direct ophthalmoscopy allows detailed assessment of the posterior pole (disc, macula, arcades). For peripheral assessment — particularly when looking for NVE — indirect ophthalmoscopy or slit-lamp with a Volk lens (90D or 78D) is required.

Slit-lamp biomicroscopy with a Volk lens (90D or 78D): allows stereoscopic, magnified assessment of the posterior pole including the macula — the most sensitive clinical method for detecting CSME before OCT is available.

Optical Coherence Tomography (OCT): the definitive investigation for diabetic macular oedema (DME). OCT provides cross-sectional images of the retinal layers and measures retinal thickness in micrometres with high precision, identifying centre-involved DME that may not be visible clinically. OCT guides anti-VEGF injection decisions and monitors treatment response. It is now the standard of care in DME management.

Fluorescein Fundus Angiography (FFA / FA): intravenous fluorescein dye is injected and photographed as it transits the retinal vasculature. FFA reveals: microaneurysms (hyperfluorescent dots), leakage sites (pooling of dye in oedema), areas of non-perfusion (hypofluorescent dark areas — 'capillary drop-out'), and the extent of neovascularisation. It guides focal laser treatment for CSME and is used in research and pre-laser planning. Note: FFA carries a small risk of anaphylaxis.

Fundus photography: wide-field retinal photography is used in screening programmes to document and grade retinopathy severity without requiring an ophthalmologist on site. Grading is performed remotely. The National Programme for Control of Blindness uses this approach for community screening in India.

Differential Diagnosis of Retinal Haemorrhages and Exudates

Not every fundus with haemorrhages and exudates is diabetic retinopathy. Making the correct diagnosis requires integrating the fundoscopic pattern with the clinical history. The following conditions can produce similar appearances and must be systematically distinguished.

Hypertensive retinopathy is the closest mimic. Both conditions produce flame haemorrhages, hard exudates, and cotton-wool spots. The distinguishing features: in hypertensive retinopathy, arterial changes predominate — arterial narrowing, increased light reflex ('silver/copper wiring'), AV nipping, and flame haemorrhages in the nerve fibre layer (rather than the dot-blot deeper haemorrhages of DR). Hard exudates in hypertensive retinopathy may form a macular star (radiating lines toward the fovea, following Henle's fibre layer). Haemorrhages are predominantly flame-shaped and follow nerve fibre layer anatomy. The history of hypertension without diabetes is the key clinical discriminator. In many Indian patients, both conditions coexist, making each condition worse.

Branch retinal vein occlusion (BRVO) produces sector-distributed flame haemorrhages, hard exudates, and macular oedema, all confined to one retinal sector (the segment drained by the occluded branch vein). The sector distribution is the key differentiating feature — diabetic retinopathy typically produces a more diffuse bilateral bilateral pattern, whereas BRVO is unilateral and strictly segmental.

Central retinal vein occlusion (CRVO) produces 'blood and thunder' fundus — dense flame haemorrhages in all four quadrants, markedly dilated and tortuous veins, disc oedema. The veins are the dominant feature. Diabetic retinopathy haemorrhages are dot-blot (deep) rather than flame (superficial) in the early stages, and veins show beading rather than gross dilatation.

Radiation retinopathy following radiotherapy to the head/neck or orbit can produce a fundoscopic picture resembling diabetic retinopathy (microaneurysms, cotton-wool spots, hard exudates) — the history of prior radiation is the diagnostic clue.

Systemic considerations: anaemia, sickle cell disease, and leukaemia can also produce retinal haemorrhages; Roth spots (haemorrhages with pale centres, seen in bacterial endocarditis, leukaemia, and anaemia) are a distinctive finding not seen in uncomplicated DR.

Management: Systemic Control, Laser, Anti-VEGF, and Surgery

Management of diabetic retinopathy is staged according to disease severity and is fundamentally a collaborative effort between the physician managing systemic disease and the ophthalmologist treating the eye. This collaboration matters because the two most powerful interventions — tight glycaemic control and blood pressure optimisation — lie entirely within the physician's domain, while laser photocoagulation, anti-VEGF injections, and vitreoretinal surgery lie within the ophthalmologist's. Delaying systemic optimisation while awaiting ophthalmological treatment is a common and costly error — both must proceed simultaneously and continuously. The framework for management is therefore best understood in two layers: the systemic layer that applies at every stage of retinopathy, and the stage-specific ophthalmic layer that escalates as the disease progresses through NPDR to PDR and into its complications. Understanding both layers allows the physician to function as an effective co-manager of the diabetic eye, not merely a referrer.

Systemic control — the foundation of all stages:
- Glycaemic control: achieving and maintaining HbA1c <7% (per ADA guidelines) is the most powerful intervention to prevent onset and slow progression of DR. The DCCT (Type 1 DM) and UKPDS (Type 2 DM) trials conclusively demonstrated that tight glycaemic control reduces the incidence and progression of DR by 50-76%. This must be optimised regardless of retinopathy stage.
- Blood pressure control: target BP <130/80 mmHg in diabetics. Hypertension independently worsens DR progression. ACE inhibitors and ARBs have specific renal and possibly retinal protective effects.
- Lipid control: statins reduce hard exudate burden in DR; fenofibrate (FIELD and ACCORD-Eye trials) has a specific retinal benefit in reducing progression, beyond its lipid-lowering effect.

Stage-specific ophthalmic treatment:

Mild–moderate NPDR without CSME: systemic optimisation; ophthalmological review every 6–12 months; no laser or injection indicated.

Severe NPDR: systemic optimisation; consider prophylactic PRP to reduce progression to PDR (especially in patients with unreliable follow-up, high-risk features, or before planned cataract surgery).

PDR: Pan-retinal photocoagulation (PRP) — laser applied to the peripheral ischaemic retina to destroy the source of VEGF production. Reduces the drive for neovascularisation. The ETDRS demonstrated that PRP reduces severe visual loss by >50% in high-risk PDR. Intravitreal anti-VEGF (ranibizumab, bevacizumab, aflibercept) can additionally suppress neovascularisation and is particularly useful when the disc and macula cannot be treated simultaneously, or when vitreous haemorrhage obscures laser delivery.

CSME / Centre-involved DME: Intravitreal anti-VEGF injection is now first-line treatment for centre-involved DME (DRCR.net Protocol T: aflibercept, bevacizumab, ranibizumab all effective; aflibercept superior when baseline VA <20/50). Focal/grid laser photocoagulation (treating leaking microaneurysms in the macular area) was the ETDRS gold standard for CSME before anti-VEGF era; now used adjunctively or in non-centre-involving DME. Intravitreal dexamethasone implant (Ozurdex) is an alternative for DME in pseudophakic or refractory patients.

Advanced PDR complications: Pars plana vitrectomy is indicated for: non-clearing vitreous haemorrhage (>3 months), tractional retinal detachment involving the macula, and combined tractional-rhegmatogenous retinal detachment.