Retinal artery occlusion

Patients describe a sudden and painless loss of vision. It is almost always monocular vision loss (from counting fingers to light perception). The presenting visual acuity depends on the affected artery. Patients with ophthalmic artery occlusion present with the perception of light or worse (as there is no perfusion in either retina or choroid). Then, patients with central retinal artery occlusion notice vision loss over the entire visual field of that eye. In case that a patient has the presence of cilioretinal artery, they may present with vision 6/6. Patients who developed BRAO complain of hemifield visual fields defect. The majority of patients has presenting visual acuity better than 6/12.(13) Presenting visual-field defects include a central scotoma in 20%, a central altitudinal defect in 13%, and sector defects in 49%.(13)

In some cases, premonitory amaurosis fugax may be reported. Amaurosis fugax represents transient acute retinal ischemia, and typically suggests an embolic source of occlusion. The presence of amaurosis fugax also has a higher correlation with stroke than with retinal emboli alone.(14)

Patients with CRAO and ophthalmic artery occlusion may present with relative afferent pupillary defect (RAPD) regardless of macular sparing. It happens within seconds following obstruction.(15)

In CRAO, the classic findings of retinal whitening and a cherry red spot are due to opacification of the nerve fibre layer, as it becomes edematous from ischemia. The fovea is cherry red because it has no overlying nerve fibre layer. This finding may take hours to develop, and the oedema is associated with a worse prognosis than without oedema. Over the course of about a month, the inner retina becomes atrophic as the swelling resolves. In patients those with the presence of cilioretinal artery, the retinal whitening will be clearly demarcated around the area of preserved macula, perfused by the cilioretinal circulation.

Examination of the retinal blood vessels shows segmental blood flow, classically described as “boxcarring”. Remember that over the course of about a week, the vessels reperfuse.

Retinal emboli are visible in 20 to 40% of eyes with CRAO.(16) Cholesterol emboli are often small, do not completely obstruct retinal arterial blood flow, and are frequently found at bifurcation sites.

If the cause of central retinal artery occlusion is giant cell arteritis, the optic disc is oedematous. In other cases, the optic disc can be normal, hyperaemic, oedematous, and sometimes pale.

In patients with BRAO, sectoral pattern of retinal opacification is seen. The whitening is most prominent in the posterior pole along the distribution of the obstructed vessel. Areas of more intense whitening are often seen at the borders of the ischemic area.

Patients with CLRAO present with whitening of the central retina, which corresponds with the course of the artery. Those patients may have optic disc oedema or intraretinal haemorrhages, depending on whether the CLRAO is associated with other conditions (Anterior Ischemic Optic Neuropathy (AION) or Central Retinal Vein Occlusion (CRVO)).

Chronic signs of retinal artery occlusion include pale optic disc, thinned retinal tissue, attenuated vessels, retinal pigment epithelial mottling, and severely decreased vision. In the case of BRAOs, there may be artery-to-artery anastomoses.(17)

Keep in mind that patients with CRAO and ophthalmic artery occlusion may develop rubeosis iridis (new vessels of the iris) in 16 to 18% of cases.(18-20) Usually, it develops in the more chronic phase of the disease, but earlier than is case in central retinal vein occlusion (4-5 weeks versus 5 months). Patients with rubeosis iridis may develop high intraocular pressure. And, patients with CRAO may also develop neovascularisations of the optic disc, which is rare.

Slit lamp examination and/or colour fundus photos – useful to recognise classic clinical signs of retinal artery occlusions.

Optical coherence tomography – a very useful tool to correctly diagnose the retinal artery occlusions. The CRAO, BRAO and CLRAO have typical appearance of hyperreflectivity of inner retinal layers (acute phase). There is no presence of retinal thickening. In the chronic phase (after one month following presentation), the inner retina is thinned.

Visual fields – can be used as part of ancillary tests, although it is not a common diagnostic tool for RAOs. Patients with sparing of the cilioretinal artery in CRAO cases may have preserved central fields. Other CRAO cases have generalised visual fields loss.

Retinal artery occlusion is an eye emergency. Patients should immediately be referred to the nearest hospital emergency room, with a stroke unit, for further management.

An erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and complete blood count (CBC) with platelets should be obtained in patients over the age of 50 who have symptoms of giant cell arteritis.(21)

Patients younger than 50 years should have a hypercoagulable workup. In a young patient with multiple or recurrent BRAOs, Susac syndrome should be considered.(21)

In older patients, atherosclerosis and emoboli are the most likely cause of the ischemia. Evaluation of the heart with echocardiography should be performed to determine cardiac function and abnormalities of the valves. Electrocardiograms and heart monitoring may reveal a rhythm defect. Cartotid artery stenosis should be evaluated with carotid ultrasound.(21)

There are no evidence-based therapies that have demonstrated efficacy in improving visual outcomes, and a meta study has suggested that some therapies may be worse than the natural course.(22)

Ocular massage is a conservative therapy that may theoretically cause emboli to travel more distally to reduce the area of ischemia. A three-mirror contact lens is placed on the eye and pressure is applied for ten seconds to obtain retinal artery pulsation or flow cessation followed by a five-seconds release.(23)