Lucan · Conditions

Diabetic retinopathy

Australian guidance: NHMRC Guidelines for the Management of Diabetic Retinopathy + RANZCO diabetic retinopathy screening/referral guidance + KeepSight (Diabetes Australia/RANZCO/Optometry Australia/Vision 2020 Australia/The Fred Hollows Foundation) + eTG Endocrinology + HealthPathways WA

1. Definition and epidemiology

Diabetic retinopathy is a progressive microvascular complication of diabetes mellitus in which chronic hyperglycaemia damages the retinal capillary network, producing a spectrum of disease from clinically silent microaneurysms through to sight-threatening neovascularisation and macular oedema. It is the leading cause of preventable vision loss in working-age Australians, and its prevalence tracks duration of diabetes rather than age: after roughly twenty years of type 1 diabetes, almost all patients have some degree of retinopathy (a classic figure from the Wisconsin Epidemiologic Study of Diabetic Retinopathy cohort, still widely taught, though contemporary well-controlled cohorts trend lower with modern glycaemic and blood pressure management), and a substantial proportion of people with type 2 diabetes already have detectable retinopathy at the time of diagnosis, reflecting years of unrecognised hyperglycaemia that preceded formal diagnosis. Across the Australian diabetic population as a whole, around one in three people with diabetes has retinopathy of some grade at any given time, and diabetic macular oedema rather than proliferative disease is the more common cause of vision impairment overall. Aboriginal and Torres Strait Islander Australians carry a disproportionately higher burden of both diabetes and diabetic retinopathy, with earlier onset, faster progression, and higher rates of vision-threatening disease at presentation, which underpins the specific screening provisions discussed below.

2. Pathophysiology

Chronic hyperglycaemia injures the retinal microvasculature through several converging biochemical pathways. Excess intracellular glucose is shunted through the polyol pathway, in which aldose reductase converts glucose to sorbitol; sorbitol accumulates within pericytes and retinal capillary cells, drawing in water osmotically and depleting NADPH needed for antioxidant defence, and pericytes are selectively lost as a result. Hyperglycaemia also drives non-enzymatic glycation of structural proteins to form advanced glycation end-products (AGEs), which cross-link basement membrane collagen and thicken the capillary basement membrane, and activates protein kinase C via increased diacylglycerol, which alters retinal blood flow and vascular permeability. Together with hyperglycaemia-driven oxidative stress, these pathways produce the two structural hallmarks of early diabetic microangiopathy: selective loss of pericytes, which normally regulate capillary tone and stabilise the endothelium, and thickening of the capillary basement membrane, both of which weaken the vessel wall (Robbins Ch 24).

Pericyte dropout leaves the capillary wall focally weakened, and outpouching at these weak points forms the microaneurysm, the earliest ophthalmoscopically visible sign of diabetic retinopathy. Breakdown of the tight junctions between retinal capillary endothelial cells disrupts the inner blood-retinal barrier, allowing plasma constituents, including lipoproteins, to leak into the retina and deposit as hard exudates, and allowing fluid to accumulate within the retina as oedema. In parallel, progressive capillary occlusion from endothelial injury, leucocyte plugging, and a locally pro-thrombotic state produces areas of retinal non-perfusion and ischaemia; ischaemic retina responds by markedly upregulating vascular endothelial growth factor (VEGF), and it is this VEGF signal that drives both the increased vascular permeability underlying macular oedema and, once ischaemia is extensive enough, the growth of fragile new vessels characteristic of proliferative disease. This shared final pathway, VEGF released by ischaemic retina, is the mechanistic reason anti-VEGF therapy is effective across both diabetic macular oedema and proliferative diabetic retinopathy despite their different clinical appearances.

3. Clinical presentation and diagnostic criteria

Diabetic retinopathy is characteristically asymptomatic in its earlier stages, which is precisely why structured screening rather than symptom-triggered review is the basis of Australian guidelines. Non-proliferative diabetic retinopathy (NPDR) is graded on fundoscopic signs into mild, moderate, and severe categories. Mild NPDR shows microaneurysms only. Moderate NPDR adds dot-and-blot intraretinal haemorrhages (haemorrhages confined to the deeper retinal layers, in contrast to flame-shaped haemorrhages arising more superficially in the nerve fibre layer, which are less characteristic of DR and classically associated with hypertensive retinopathy), hard exudates (well-defined yellow-white lipid deposits at the margin of leaking capillaries), and cotton-wool spots (soft, ill-defined white patches representing microinfarcts of the nerve fibre layer, from focal capillary occlusion rather than lipid leakage). Severe NPDR is defined by the 4-2-1 rule: severe intraretinal haemorrhages in all four fundus quadrants, definite venous beading (irregular, sausage-like dilation of retinal veins signalling widespread ischaemia) in two or more quadrants, or prominent intraretinal microvascular abnormalities (IRMA, dilated pre-existing capillary shunts within the retina that mimic early neovascularisation but remain confined to the retinal plane) in at least one quadrant; meeting any one of these criteria confers a high short-term risk of progression to proliferative disease.

Proliferative diabetic retinopathy (PDR) is defined by neovascularisation, new vessel growth driven by VEGF from ischaemic retina that breaks through the internal limiting membrane and grows along the retinal surface or into the vitreous cavity. Neovascularisation is described as at the disc (NVD) when it arises at or within one disc diameter of the optic nerve head, or elsewhere (NVE) when it arises more peripherally; disc neovascularisation carries the highest risk of severe vision loss because of its central location and heavy blood supply. These new vessels lack the structural integrity of normal retinal vasculature and readily bleed, producing a vitreous haemorrhage that presents as sudden floaters, cobweb-like shadows, or profound vision loss depending on volume. Accompanying fibrovascular proliferation can contract over time and pull the retina away from the underlying retinal pigment epithelium, causing a tractional retinal detachment, and in advanced ischaemic disease the same VEGF drive can cause neovascularisation of the iris (rubeosis iridis), which can obstruct the trabecular meshwork or angle and precipitate neovascular glaucoma, a painful and vision-threatening emergency.

Diabetic macular oedema (DMO) can develop at any stage of retinopathy, non-proliferative or proliferative, because it results from local breakdown of the blood-retinal barrier rather than from the global burden of retinal ischaemia; oedema and hard exudates within the macula are graded as clinically significant when they meet ETDRS criteria based on thickening or exudate within or near the centre of the fovea, and centre-involving DMO threatens reading and detailed central vision directly. Because DMO can be present with otherwise mild retinopathy elsewhere in the fundus, macular assessment is a distinct step in every diabetic eye examination rather than an incidental finding on peripheral grading. Clinically, patients with early NPDR or non-centre-involving DMO are typically asymptomatic; blurred or distorted central vision suggests centre-involving DMO, while sudden floaters or profound vision loss suggest vitreous haemorrhage, and a curtain-like visual field defect suggests tractional retinal detachment, each representing a later and more urgent stage of disease than the asymptomatic majority of patients being screened.

4. Investigations and AU-specific cutoffs

Screening is performed by dilated fundus examination or retinal photography, and Australian intervals are set out in the NHMRC Guidelines for the Management of Diabetic Retinopathy and reflected in RANZCO and HealthPathways WA referral pathways. In type 1 diabetes, screening begins within five years of diagnosis (or from puberty if diagnosed before puberty, given retinopathy is rare before this) and continues annually thereafter. In type 2 diabetes, screening begins at the time of diagnosis, reflecting the likely years of unrecognised hyperglycaemia beforehand, and continues at least every two years if no retinopathy is found and glycaemic control is satisfactory, or annually once any retinopathy is present or other risk factors apply. Higher-risk groups are screened more frequently regardless of these baseline intervals: pregnancy in a woman with pre-existing diabetes is associated with rapid retinopathy progression and is screened each trimester, and more frequent review is also indicated for poor glycaemic control, longer diabetes duration, coexisting hypertension, and diabetic kidney disease. Aboriginal and Torres Strait Islander people with diabetes are recommended annual retinal screening from the time of diagnosis regardless of diabetes type, consistent with the National Guide to Preventive Healthcare for Aboriginal and Torres Strait Islander People (RACGP/NACCHO), reflecting both the higher background prevalence of retinopathy in this population and the barriers that distance and service access can otherwise place between screening and timely treatment.

KeepSight, a national reminder program run jointly by Diabetes Australia, RANZCO, Optometry Australia, Vision 2020 Australia, and The Fred Hollows Foundation, was established because historically only around half of Australians with diabetes attended regular eye examinations despite the guideline recommendations above; patients are registered at the point of an eye examination and receive automated reminders timed to their individually recommended screening interval. In regional and remote Western Australia, where the distance to a specialist ophthalmologist can itself be the dominant barrier to screening, non-mydriatic retinal camera outreach programs and store-and-forward teleophthalmology, where a locally acquired retinal photograph is transmitted for remote grading by an ophthalmologist, are used to bring screening to Aboriginal community-controlled health services and remote clinics rather than requiring patients to travel, and are a specific focus of KeepSight's Aboriginal and remote outreach activity.

Beyond grading photography, optical coherence tomography (OCT) provides a cross-sectional image of the macula and is the primary tool for quantifying and monitoring macular thickening in DMO, while fundus fluorescein angiography (FFA) demonstrates areas of capillary non-perfusion and vascular leakage and is used selectively to confirm the extent of ischaemia or neovascularisation and to guide laser treatment when the clinical picture is equivocal.

5. Management

Systemic risk factor control is the foundation of management at every stage and is emphasised throughout eTG Endocrinology and Australian diabetes guidelines because it is the only intervention that slows the biological process driving retinopathy rather than treating its downstream consequences. Intensive glycaemic control, targeted per individualised HbA1c goals, produces a substantial reduction in the incidence and progression of microvascular complications including retinopathy, an effect demonstrated across both type 1 and type 2 diabetes; blood pressure control to standard Australian targets similarly reduces retinopathy progression, reflecting the added microvascular stress that systemic hypertension places on an already compromised capillary bed; and smoking cessation and attention to dyslipidaemia round out the modifiable risk factors addressed alongside ophthalmic review, since none of the eye-directed treatments below substitute for this systemic control.

Referral thresholds are set out in RANZCO and HealthPathways WA pathways: any centre-involving DMO, any severe NPDR, and any PDR warrant referral to an ophthalmologist for treatment, while vitreous haemorrhage or a tractional retinal detachment threatening or involving the macula warrants urgent or same-day referral. Intravitreal anti-VEGF injection has become first-line treatment for centre-involving DMO and is increasingly used in PDR, working by directly blocking the VEGF signal responsible for both vascular permeability and neovascularisation; it typically requires a monthly loading phase followed by an individualised treat-and-extend regimen, and sustained benefit depends on the patient's capacity to attend for repeated injections. Panretinal photocoagulation (PRP), laser ablation of the peripheral ischaemic retina, remains a guideline-endorsed mainstay for PDR: by destroying oxygen-hungry peripheral retinal tissue it reduces the overall VEGF drive from the eye, and pivotal trials underpinning the NHMRC guideline demonstrated roughly a halving of severe vision loss with PRP in high-risk PDR, though PRP does not restore lost vision and carries recognised side effects of peripheral visual field constriction and impaired night vision. In the Australian regional and remote context, where returning monthly for anti-VEGF injections may not be feasible, PRP's durability as a largely one-off treatment is a practical as well as clinical consideration. Focal or grid laser to the macula remains an option for non-centre-involving DMO but has been superseded by anti-VEGF as first-line therapy for centre-involving disease. Pars plana vitrectomy is reserved for vitreous haemorrhage that fails to clear, or for tractional retinal detachment threatening or involving the macula.

6. Pharmacology and AU PBS notes

Ranibizumab (Lucentis) and aflibercept (Eylea) are PBS-listed intravitreal anti-VEGF agents for DMO, subject to authority criteria that specify baseline visual acuity and response-based rules for continuing therapy; faricimab (Vabysmo), a newer agent that additionally blocks the angiopoietin-2 pathway alongside VEGF-A, is also PBS-listed and allows longer dosing intervals in responders. Anti-VEGF agents are increasingly used for PDR as well as DMO, though PRP remains the guideline-endorsed default for PDR in Australian practice, particularly where sustained follow-up for repeated injections cannot be guaranteed. Fenofibrate, PBS-listed for dyslipidaemia, has trial evidence from the Australian-led FIELD study for reducing the need for laser treatment in diabetic retinopathy through a mechanism independent of its lipid-lowering effect, and is considered by some Australian diabetes management pathways as an adjunct in patients already requiring lipid therapy. There is no PBS-listed oral or topical agent that treats retinopathy directly; all pharmacological benefit for the eye itself comes from intravitreal anti-VEGF, with systemic agents (glucose-lowering therapy, antihypertensives, fenofibrate) acting on the upstream risk factors rather than the retina.

7. Complications and monitoring

The principal vision-threatening complications are vitreous haemorrhage from bleeding new vessels, tractional retinal detachment from contracting fibrovascular membranes, and neovascular glaucoma from angle neovascularisation, each of which represents a late consequence of unchecked retinal ischaemia and VEGF drive and each of which is materially reduced by timely PRP or anti-VEGF treatment before this stage is reached. Patients treated with anti-VEGF or laser require structured, guideline-defined ophthalmology follow-up rather than a return to routine screening intervals, since both DMO and PDR can recur or progress between treatments. Once any retinopathy is identified on screening, review reverts to at least annual ophthalmic assessment regardless of the baseline interval that applied beforehand, and systemic risk factor control is reinforced at every review, since glycaemic and blood pressure control continue to influence progression even after eye-directed treatment has begun.

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.