The fundamental pathomechanism is: Hyperglycemia → damage to endothelial wall and pericytes
This process has several important effects:

• Pericyte damage → microaneurysms → flame haemorrhages (nerve fibre layer)
• Infarcts → cotton wool spots (axonal debris at infarct margins) (nerve fibre layer)
• Increased vessel permeability → Hard exudates (lipoproteins in outer plexiform layer)
• Cystoid macular oedema (outer plexiform layer)
• Neovascularization

The most important risk factor for the progression of diabetic retinopathy is the duration of diabetes

Most cases are picked up with diabetic screening but there are 3 associated presentations to be aware of:

• Acute painful vision loss: Neovascular Glaucoma
• Flashes/Floaters then painless vision loss: Vitreous haemorrhage or retinal detachment
• Gradual vision loss: Retinopathy or macular oedema or cataract

Nonproliferative

• Background
  • Any of: microaneurysms, retinal haemorrhages, venous looping
  • Occasional cotton wool spots and hard exudates
• Pre-proliferative
  • Any of: multiple dot and blot haemorrhages, venous beading, intraretinal microvascular abnormalities (IRMA)

Proliferative

• Any neovascularization OR Vitreous haemorrhage OR Pre-retinal haemorrhage

Macular oedema

• Clinically significant macular oedema
  • Retinal thickening/hard exudates within 500um of fovea
  • Centre involving diabetic macular oedema

Classification is important for risk stratification and subsequent management

The management options are chosen based on risk classification

• Non-proliferative → Monitoring
• Proliferative → Panretinal photocoagulation (PRP) of the retina
• Clinically significant maculopathy (including oedema) → Macular grid laser
• Diabetic macular oedema → Anti-VEGF or OZURDEX® (steroid implant)

If the patient also has cataracts, treat diabetic complications before cataracts are addressed

1. Arteriolar narrowing
2. AV nipping OR silver wiring
3. Flame haemorrhages OR cotton wool spots
4. Disc swelling OR hard exudates OR retinal oedema

• Treatment is focused on targeting systemic hypertension.
• Patients with papilloedema and malignant hypertension need emergency assessment (discussed in detail in the Neuro-ophthalmology chapter)

Obstruction of retinal arteries is considered a STROKE

The differentiation of these conditions based on clinical signs is both highly examinable and clinically important.

An ophthalmic emergency which can lead to irreversible vision loss. THIS IS A STROKE

Pathology

• Occlusion of the retinal artery → hypoxia of the retina → cell death and neovascularization.
• Systemic causes of arterial occlusion apply just the same to the retinal artery, with the most common cause being atherosclerosis.
• Irreversible infarction occurs within 90 minutes of CRAO
• The most common cause of BRAO is emboli

Diagnostics

• Diagnosis is made clinically and is clear in the acute presentation but OCT can be useful in less clear cases and delayed presentations**,** where inner retinal atrophy can be seen
• It is important to look for specific aetiology based on the presentation and look to treat underlying causes
  • 50-year-old woman with headaches → GCA?
  • 70-year-old male smoker with diabetes and carotid bruit → carotid embolism?

Management

• Initial management of CRAO (within 24 hours) : Ocular massage + IV acetazolamide +- AC paracentesis
• No specific treatment for BRAO, but they should be urgently referred to the stroke team.

Around 30% of the population have a cilioretinal artery which provides anastomosis between the central retinal artery (supplying the inner 2/3 of the retina) and choroidal vessels (outer 2/3 of the retina).

Retinal vein occlusion is the 2nd commonest retinal vasculopathy (to DR).

Pathology

• Occlusion of retinal veins can cause ischemia, haemorrhage and oedema.
• It can lead to complications such as neovascularization and oedema, which negatively reduces vision.

Types

• CRVO → occlusion proximal to the lamina cribrosa
• BRVO → occlusion of branch of central retinal vein
• Ischemic type is associated with a higher risk of neovascularization and a poorer visual prognosis
  • Ischemia is picked up by worse symptoms and additional ischemic signs such as RAPD, rubeosis iridis and non-perfusion on FFA.

Diagnostics

• Patients are worked up for systemic risk factors for thrombosis including general bloods, diabetic screen and blood pressure. Keep a high index of suspicion for vasculopathies and thrombophilias in suggestive presentations.
• FFA is abnormal
• OCT is useful to identify and monitor macular oedema (thick on OCT)

Management

• Treatment is guided by specific complications which in turn determine visual prognosis.
• Neovascularization → Panretinal photocoagulation (PRP) laser (sectoral for BRVO)
• Macular oedema → Anti-VEGF or Ozurdex® (dexamethasone implant)

• Most commonly caused by atherosclerosis.
• As with other causes of ocular ischemia, this can lead to neovascularization of intraocular structures such as the retina and iris.

Presentation

• The patient is typically an elderly male with a history of vascular risk factors such as diabetes, smoking and hypertension
• Painful gradual reduction in vision with episodes of transient vision loss (amaurosis fugax) and orbital aching pain

Investigations

• Examination might show flare in the anterior chamber

• Focused on relieving the carotid obstruction by stenting or endarterectomy

• Sickling of cells leads to occlusion and ischemia. This can subsequently lead to proliferative changes and neovascularization.
• There are 2 types: proliferative and nonproliferative
• Severity of disease is determined by mutation, from mild to severe: HbSC → HbSTHal → HbSS

Presentation

• Nonproliferative: Salmon patches (intraretinal haemorrhages and black sunbursts (RPE hyperplasia)
• Proliferative: sea fan neovascularization, vitreous haemorrhage and retinal detachment

Investigations

• Diagnosis of Sickle cell is made by haemoglobin electrophoresis

Proliferative sickle cell retinopathy is categorised according to the Goldberg classification.

• Scatter laser photocoagulation can be used in severe sickle cell retinopathy