Pathophysiology
Diabetic retinopathy is the most common cause of blindness in individuals aged 35-65 years old.
With poorly managed glycemic control, we get chronic hyperglycaemia which can induce changes to the retinal neurovasculature in a few ways:
- Damage to blood vessels
- Microaneurysms - weakened blood vessels start to get aneurysms. This is similar to any other aneurysm where we get pericyte and endothelial damage which impairs the integrity of the vessel.
- Venous beading - irregular constriction and dilation of the venules within the retina leading to a sausage-shaped dilation and constriction in the veins (regions of constriction followed by regions of dilation).
- Increased vascular permeability
- Blood leakage - blood leaking into the vitreous humour → blot haemorrhages.
- Lipid leakage - lipid leakage into the retina leads to hard exudate formation.
- Damage to nerve fibres - seen as cotton wool spots which are soft exudates that form due to ischaemia to nerve axons.
- Intra-retinal microvascular abnormalities (IRMA) - shunt vessels are seen which are tortuous and dilated. IRMA appears deeper in the retina than neovascularization, has blurrier edges, is more of a burgundy than a red, does not appear on the optic disc, and is usually seen after a shorter period of poorly controlled diabetes than neovascularization.
- Neovascularisation/new vessel disease (NVD) - due to ischaemia we get increased VEGF → neovascularisation. However, these new vessels are small and weak and are prone to rupture and leakage, which leads to a vitreous haemorrhage.
🔢 Classification
Non-proliferative diabetic retinopathy (NPDR)
- Mild - 1+ microanuerysm
- Moderate - microaneurysms, blot haemorrhages, hard exudates, cotton wool spots.
- Severe - blot haemorrhages in all 4 quadrants. Venous beading in 2 or more quadrants. IRMA in at least 1 quadrant.
Proliferative diabetic retinopathy (PDR)
Neovascularisation is the distinction.
It is more common in type 1 DM and 50% of patients become blind within 5 years.
Diabetic maculopathy
The distinction is that it occurs over the macula. It is more common type 2 DM. As the macula provides the greatest visual acuity, visual acuity will be affected.
😷 Presentation
It is usually asymptomatic until quite a progressed stage of the disease. Some things that the patient may report are:
- Reduction in visual acuity
- Floaters
- Eye pain
- Impaired vision in the dark
- Vision loss - can be gradual or may be of sudden onset.
Most patients will only present with the retinal changes on fundoscopy:
- Microaneurysms
- Blot haemorrhages
- Neovascularisation of small vessels
- Hard exudates
- Soft exudates/cotton wool spots
🔍 Investigations
🏆 Fundoscopy will be the only way we can visualise the retina and diagnose the disease.
🧰 Management
It depends on the type of diabetic retinopathy the patient has. However, glycemic control, BP management, and lipid management should be optimised.
Non-proliferative diabetic retinopathy (NPDR)
Regular observation is all that is needed.
Diabetes control needs to be optimised.
Pan-retinal laser photocagulation may be considered only in severe cases.
Proliferative diabetic retinopathy (PDR)
🥇 Pan-retinal laser photocoagulation
Intravitreal VEGF inhibitors
- Ranbizumab - prevents neovascularisation and slows progression.
If there has been a severe vitreous haemorrhage then vitrectomy may be indicated. Here the vitreous humour is removed and a synthetic version is implanted in its place.
Diabetic maculopathy
Intravitreal VEGF inhibitors is indicated if there are changes to visual acuity.
🚨 Complications
- Retinal detachment
- Vitreous haemorrhage
- Rebeosis iridis - this is when new vessels form in the iris.
- Optic neuropathy
- Cataracts
👀 Screening
Diabetic eye screening is used to assess for any signs of proliferative diabetic retinopathy.
Everyone with diabetes over 12 years old will get an invite. Initially, the invite should be every year but this can change depending on the results.
With diabetic retinopathy screening, the eyes are inspected followed by testing visual acuity, the fundus is then assessed with fundus photography.
Results | Next steps |
R0 - No retinopathy | Continue regular screening |
R1 - Background changes | May be asked to return sooner |
R2 - Non-proliferative retinopathy | More regular screening |
R3 - Proliferative retinopathy | Referral to ophthalmology for treatment options. |
An M1 may indicate maculopathy too.