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The most common causes of sudden profound vision loss are vascular and include:

• Central retinal vein occlusion (CRVO)
  
• Central retinal artery occlusion (CRAO)
  
• Anterior ischaemic optic neuropathy (AION)
  
• Vitreous Haemorrhage

• Central retinal artery occlusion
  
• Metabolic storage disorders (e.g. Tay Sachs disease, Niemann Pick disease)

There were no symptoms of giant cell arteritis (GCA). Specifically the patient did not report jaw claudication, temporal and scalp tenderness, headache, neck stiffness or systemic malaise.

Optical coherence tomography (OCT) through the right macula demonstrated hyperreflectivity within the inner retinal layers. This was not evident in the left macula on OCT (Figure 3).

A fluorescein angiogram was not performed as the diagnosis was clinical and angiography would not add further to the patient’s management. As the CRAO had been established for 24 hours, no ophthalmic treatment was recommended, as the retinal damage was irreversible.

After discussion with the patients’ general practitioner, aspirin was commenced and arrangements made for the patient to see a cardiologist. Electrocardiography (ECG) and cardiac echocardiography were normal. A carotid Doppler study, arranged to detect any carotid disease as the potential source of the embolus, demonstrated 70% stenosis on the right side and complete stenosis on the left. Subsequent consultation with a vascular surgeon recommended carotid endarterectomy. Vascular risk factors were checked.

Three weeks later visual acuity was still hand movements. The retinal pallor and cherry red spot had partially resolved, but the retinal embolus remained in the same positions. Disc pallor was developing and cilioretinal collaterals were evident (Figure 4). There was no iris or angle rubeosis.

Central retinal artery occlusion (CRAO) is analogous to a stroke of the eye. As a result of interruption to the arterial supply of the inner retina, patients present with severe unilateral painless visual loss. While the cherry red spot is the classical finding in CRAO, it is a consequence of retinal ischaemia and infarction and may not be present or easy to recognise within a few hours of the occlusion. Other important clinical findings in this early stage include a relative afferent pupillary defect, retinal arteriolar attenuation, segmentation of the arteriolar blood column (“cattle trucking”) and emboli. The OCT will demonstrate inner retinal hyperreflectivity, as in this patient, corresponding to oedema, remembering that the retinal vascular system supplies only the inner retina with the outer retina receiving its metabolic supply from the choroid. Fluorescein angiography will demonstrate delayed filling of the occluded retinal artery system but is usually not required.

Emboli are the most common cause of CRAO and most often arise from the carotid arteries.(1) Accordingly patients with CRAO need a “stroke work up” with their general practitioner and physician with special attention to diagnosing and treating carotid disease (carotid ultrasound), cardiac disease (ECG to exclude arrhythmias, cardiac echocardiography for valvular disease or a mural thrombus) and cardiovascular risk factor control (hypertension, hypercholesterolaemia, hyperglycaemia and smoking cessation).

This patient demonstrates a calcific embolus. These are typically large chalky-white plaques found near the optic optic disc with a high risk of obstruction, as in this case. They are associated with cardiac valves calcification and carotid artery plaques. Other retinal arteriolar emboli that may be seen include cholesterol emboli (“Hollenhorst plaques”) and fibrinoplatelet plaques. Cholesterol emboli are smaller thin brightly reflective yellow plaques that unless large do not cause complete occlusion of the artery and are therefore often asymptomatic. They usually arise from atheromatous plaques in the aortic and carotid system. Fibrinoplatelet plaques are duller, grey and elongated, running partially along the length of an arteriole.

Just under 5% of cases of CRAO are due to giant cell arteritis (GCA).(2) In patients in whom an embolus cannot be seen and/or who have symptoms of GCA further investigation is required as this diagnosis has serious implications for vision loss in the fellow eye and requires prompt steroid treatment.

The acute treatment of CRAO involves attempting to restore central retinal artery blood supply. After 4 to 6 hours with no retinal blood supply the retina is irreversibly damaged so prompt intervention is required.(1,3) Unfortunately most patients present after this window so interventions are unlikely to be helpful.(1,3) Interventions to distalise the embolus including digital massage, hyperventilation manoeuvres and intraocular pressure lowering (medication and anterior chamber paracentesis) have only been reported in observational studies and probably do not add much beyond the natural history of the condition.(1,3)

Thrombolysis, which is used to treat ischaemic stroke within the first hours of presentation, has also been investigated in CRAO.(1,3) Thrombolytic medication is aimed at dissolving the clot to allow reperfusion. It is injected either via a peripheral vein (intravenous) or directly into the carotid or ophthalmic artery via catheter (local arterial) by an interventional neuroradiologist. There is considerable controversy regarding the benefit and also potential significant safety consideration such as stroke.(1,3) In any case only a minority of patients will present within the window for this treatment to be considered.

Unfortunately, the visual prognosis for CRAO is poor with only 10% of patients reporting meaningful recovery of vision.(4) Patients still need to be observed for iris and angle neovascularisation which can occur in up to 1/3 patients.(5) The onset of neovascularisation in CRAO is often one to two months post occlusion as opposed to the traditional 90 days in central retinal vein occlusion. Treatment is with panretinal photocoagulation (PRP) to prevent neovascular glaucoma and a painful blind eye. Patients also need ongoing follow up with their general practitioner and physician to control cardiovascular risk factors and prevent further vascular events such as heart attack and stroke.