Retinal vessels occlusions Flashcards
What is the source of blood supply to the retina?
The central retinal artery (CRA) is a branch of the ophthalmic artery, which is the first branch of the internal carotid artery.
The CRA supplies blood to the surface of the optic disc. From here it divides into two main branches (superior and inferior); these then further divide into temporal and nasal branches, which supply blood to the four quadrants of the retina.
The outer retina is supplied by the choriocapillaries of the choroid that branches off the ciliary artery.
Both the CRA and the ciliary artery must be functioning to maintain retinal function, as both CRA and ciliary artery originate from the OA.
One important variation is the presence of a cilioretinal artery. This artery, thought to be present in 15-30% of people, supplies the macular retina to a varying degree and may help preserve some vision after CRAO. The cilioretinal artery is seen ophthalmoscopically as a single vessel emerging from the edge of the optic disc, most commonly towards the macula.
What is central retinal artery occlusion?
Central retinal artery occlusion (CRAO) is an ophthalmic emergency. It is one of the more common causes of severe visual impairment in elderly patients.
Depending on where the occlusion occurs, different layers and quarters of the retina can be affected: more proximal ophthalmic artery occlusion will have the most devastating effect, as all layers of the entire retina lose their blood supply, whereas a occlusion of a distal end branch of the retinal artery will only affect the inner neural retina of that part of the retina, sparing the photoreceptors and limiting visual loss.
Occlusion affecting the retinal artery prior to branching is termed CRAO. Occlusion of one of the branches of the retinal artery is referred to as branch retinal artery occlusion (BRAO).
What is the pathophysiology of CRAO?
CRAO is the ocular equivalent of cerebral stroke and is a process of end-organ ischaemia.
Many of the risk factors are those for cardiovascular and cerebrovascular disease and its occurrence is a warning sign for other vascular complications.
Embolism is the most common cause, the major source of this being carotid artery disease, usually due to atherosclerotic plaques. Carotid stenosis and the heart are other important sources of emboli.
Inflammatory- GCA, SLE, polyarteritis nodosa
Infectious origin such as toxoplasmosis, syphilis.
Pharmacological causes such as oral contraceptive pill and cocaine.
Ophthalmic causes- severely raised IOP or optic nerve drusen.
What is the presentation of CRAO?
Sudden (over a few seconds), unilateral painless visual loss.
In 94% of cases, vision is usually reduced to counting fingers (worse suggests that the ophthalmic artery may also be affected).
There may be a history of amaurosis fugax (amaurosis fugax precedes loss of vision in up to 10% of patients).
In 1-2% of patients, the loss is bilateral (although the degree is not necessarily the same in each eye).
Examination reveals an afferent pupillary defect and a pale retina with attenuation of the vessels.
There may be segmentation of the blood column in the arteries (‘cattle trucking) and the centre of the macula (supplied by the intact underlying choroid) stands out as a cherry-red spot.
Systemic examination should include carotid auscultation for bruits, heart sounds for murmurs, radial pulse for atrial fibrillation and blood pressure.
What are the differentials for CRAO?
Retinal detachment Vitreous haemorrhage Retinal vein occlusion Acute glaucoma Acute optic neuritis
What are the investigations for CRAO?
Diagnosis is usually clinical and investigations are aimed at ruling out underlying diseases.
The most important cause to rule out is giant cell arteritis because, with timely intervention, the visual loss is reversible and the fellow eye will be protected.
If there is any doubt about the diagnosis then fluorescein angiography and optical coherence tomography may be helpful.
Urgent ESR and CRP are measured in patients over 60 years of age, when a diagnosis of giant cell arteritis cannot be excluded.
Coagulation studies, full blood examination and screening tests for vasculitis are usually performed. In the longer term, cardiovascular risk assessment includes measurement of fasting blood sugar and lipid profile.
What is the management of CRAO?
Retinal artery occlusion is an ocular emergency, both because the retinal damage rapidly becomes irreversible with time and because of the urgent need to optimise management of other risk factors in order to protect both the other eye and the cerebrovascular and cardiovascular systems.
However, whilst several management options have been, and still are, employed, there is currently no evidence-based treatment to reverse the visual loss.
If giant cell arteritis is suspected, it needs immediate treatment (intravenous steroids followed by oral steroids), as it is in itself an ophthalmological emergency.
The principle of management is to attempt to reperfuse ischaemic tissue as quickly as possible and to institute secondary prevention early.
What are treatments tried for CRAO?
If the patient presents within 90-100 minutes of the onset of symptoms, firm ocular massage (repeatedly massaging the globe over the closed lid for ten seconds with five-second interludes) may dislodge the obstruction. However, this only works very occasionally.
Lowering intraocular pressure with anterior chamber paracentesis (withdrawal of a little fluid from the anterior chamber under local anaesthetic, done in the clinic), together with treatment with acetazolamide. Other intraocular pressure-lowering drugs include apraclonidine, mannitol and beta-blockers.
Dilatation of the artery (e.g., sublingual isosorbide dinitrate, inhaled carbogen or hyperbaric oxygen).
What is the long term management of CRAO?
Retinal artery occlusion is a marker for increased risk of ischaemic end-organ damage such as cerebral stroke.
Long-term management of any retinal artery occlusion therefore aims to:
- Identify and address underlying causes in order to prevent further ischaemic events (e.g., investigate and treat hypertension).
- Assess for coagulopathies - assessment should also be performed, particularly if no embolic source is found.
- Reduce risk factors for atherosclerosis: optimised management of hypertension and prophylaxis with statins and low-dose aspirin may be beneficial.
- Carotid endartectomy- may be necessary depending on the degree of carotid occlusion and local policy.
- Referral to low vision aid clinics
- DVLA notification.
What is the presentation of BRAO?
This is as for CRAO but only part of the vision is lost: the defect is usually the upper/lower half of vision or sectoral.
Retinal pallor corresponds to the area supplied by the affected artery.
Occasionally, an embolus (cholesterol, fibrinoplatelet, calcific) can be seen within the artery, and cotton wool spots may eventually occur around that area.
What is the management of BRAO?
Refer within 24 hours. However, there is no proven effective management.
Long-term management is as for CRAO.
Full and thorough assessment of the cardiovascular system as for CRAO. Carotid endarterectomy or anticoagulation may be indicated.
Thorough assessment for coagulopathies should also be performed if no embolic source is found.
What is retinal vein occlusion?
Retinal vein occlusions (RVOs) are the second most common type of retinal vascular disorder after diabetic retinal disease.
They can occur at almost any age (although typically in middle to later years - most in those aged over 65 years) and their severity ranges from asymptomatic to a painful eye with severe visual impairment.
Retinal vein occlusion is one of the most common causes of sudden painless unilateral loss of vision. Loss of vision is usually secondary to macular oedema. Occlusion may occur in the central retinal vein or branch retinal vein
What is the pathophysiology of RVO?
Occlusion of the retinal venous system by thrombus formation is the most common cause but other causes include disease of the vein wall and external compression of the vein.
Retinal arteries and arterioles and their corresponding veins share a common adventitial sheath. It is thought that the thickening of the arteriole compresses the vein, eventually causing occlusion.
A backlog of stagnated blood combined with associated hypoxia results in extravasation of blood constituents, causing further stagnation and so on, resulting in the creation of a vicious circle of events.
Ischaemic damage to the retina stimulates increased production of vascular endothelial growth factor (VEGF) which, in turn, may lead to neovascularisation - a process that can result in haemorrhage (as the new vessels are of poor quality) or neovascular glaucoma (the new vessels grow into the aqueous drainage system, so clogging it up).
What are the risk factors of RVO?
Advancing age Systemic conditions such as HTN Raised IOP/glaucoma Inflammatory diseases such as sarcoidosis, Behcet’s syndrome Thrombophilic disorders Polycyathemia
What are the investigations done for RVOs?
All patients should have:
- BP (the most common association with BRVO).
- Blood glucose and lipids (if abnormal, TFTs too).
- FBC, ESR.
- Plasma protein electrophoresis.
- ECG.
Depending on individual circumstances (e.g., a young patient), other tests may include:
- Thrombophilia screen including antiphospholipid antibodies and lupus anticoagulant.
- CRP, serum ACE, auto-antibodies, CXR, fasting homocysteine levels.
In the eye clinic, further evaluation includes:
- Measurement of intraocular pressure.
- Fluorescein angiography is the investigation of choice in CRVO. It evaluates retinal capillary non-perfusion, neovascularisation and macular oedema. It is not often necessary in BRVO.
- Optical coherence tomography angiograph (OCTA). This is non-invasive, transpupillary imaging. It measures the retina and can detect macular oedema that fluorescein angiography has missed because of blockage from haemorrhage.
