Retinal artery occlusion is characterized by sudden, painless, monocular loss of vision, most often due to an embolus occluding the central retinal artery or its branches. The diagnosis of the condition depends on clinical presentation and the classic funduscopic appearance of the retina.
Retinal artery occlusion (RAO) was first described in 1859 by von Graefe . It mainly occurs due to the occlusion of the central retinal artery (CRA) or its branches, usually by an embolus and is reported to affect approximately 2 out of every 100,000 individuals in the United States . The patients present classically with a sudden onset of unilateral, painless, visual loss which may rapidly deteriorate to the level of mere finger counting ability or even complete loss of vision  . Up to 30% of individuals have a cilioretinal artery , a branch of the short posterior ciliary artery, which may lead to significant sparing of the vision as the cilioretinal artery supplies part or the entire fovea and is unaffected in the central retinal artery occlusion.
Clinically RAO has four different entities:
- Permanent non-arteritic RAO accounts for a majority of the cases. It is caused by thrombi or emboli secondary to atherosclerosis   .
- Transient non-arteritic RAO is associated with transient monocular visual loss and has a good prognosis for regaining vision.
- Non-arteritic RAO with cilioretinal sparing results in only peripheral visual loss due to sparing of the cilioretinal artery and the macula .
- Arteritic RAO accounts for a minor percentage of RAO cases and primarily includes patients with giant cell arteritis. Patients are usually above the age of 55 years and may have a bilateral visual loss with other symptoms like a temporal headache, temporal artery tenderness, jaw claudication, and fatigue.
As already mentioned, the commonest cause of RAO is a thrombus or an embolus occluding the central retinal artery as it pierces the dural sheath of the optic nerve . Retinal recovery after RAO depends on the dislodgement of the embolus or thrombus and on the tolerance time of the retina  .
Entire Body System
Systemic evaluation revealed a history of chronic low-grade fever and generalized lymphadenopathy. HIV (ELISA) was positive, and other systemic comorbidities were ruled out. [ncbi.nlm.nih.gov]
- Cat Scratch
CONCLUSION: Cat scratch disease may cause retinal artery occlusion in infected patients, leaving them with a permanent visual field defect. [ncbi.nlm.nih.gov]
- Increased Energy
• Pulses are delivered directly to the emboli, beginning with the lowest power setting and then with increasing energy until either (1) achieving photofragmentation of the embolus within the arteriole without creating an opening in the vessel wall and [slideshare.net]
- Visual Impairment
RESULTS: A 65-year-old woman developed dramatic visual impairment in her left eye secondary to BRAO after left internal carotid artery endovascular reconstruction with flow diverter stent implant; visual acuity was hand motion. [ncbi.nlm.nih.gov]
An abrupt blockage of blood flow (ischemia) halts proper retinal functioning, which results in visual impairment. Depending on the extent and location of the retina affected, the loss of vision may be relatively mild or very severe. [midatlanticretina.com]
On the positive side doctors are looking into laser surgery and how it may help rectify retinal damage and fix the visual impairment caused by the occlusion. [kanataoptometry.ca]
On the positive side, however, doctors are investigating laser surgery to help rectify retinal damage and visual impairment caused by the occlusion of the retinal arteries. [waterdownoptometric.ca]
It may lead to severe irreversible visual impairment. This condition mostly occurs in patients with high blood pressure, heart disease, diabetes or carotid atherosclerosis in elderly people (Varma et al. 2013 ). [springerplus.springeropen.com]
- Retinal Pallor
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. [patient.info]
- Intracranial Hemorrhage
It may be a rare and underdiagnosed cause of venous and arterial thrombosis, leading to severe brain damage by cerebral edema and intracranial hemorrhage. [ncbi.nlm.nih.gov]
The study did not recommend intra-arterial tPA for acute CRAO because of significant symptomatic intracranial hemorrhage without evidence of visual benefit.  The trial was terminated early due to the adverse effects of tPA. [eyewiki.aao.org]
Intracranial hemorrhage after use of tissue plasminogen activator for coronary thrombolysis. Ann Intern Med 1990 ; 112 : 17 –21 Schmidt D, Schumacher M, Wakhloo AK. Microcatheter urokinase infusion in central retinal artery occlusion. [ajnr.org]
- Recurrent Headache
A 60-year-old woman with a history of recurrent headaches and blurred vision presented with bilateral optic disc edema. Optic neuritis was suspected, and intravenous methylprednisonlone was administered. [ncbi.nlm.nih.gov]
The diagnosis of RAO is suspected based on the clinical presentation and can be confirmed with clinical evaluation, fundoscopy, and fluorescein angiography. An ophthalmic examination may reveal a relative afferent pupillary defect while the funduscopic appearance of a pale, opaque fundus with a red fovea (cherry-red spot) is confirmatory. Occasionally, a cholesterol embolus (known as Hollenhorst plaque) may also be seen. In cases where the central retinal artery is spared and only a major branch is occluded, visual loss may be restricted to the corresponding sector of the retina. Fluorescein angiography detects the lack of perfusion in the occluded artery.
If non-arteritic permanent RAO due to thrombus or embolus is suspected then the physician should inquire about risk factors for atherosclerosis, a past history of vascular disease, cardiac disease, smoking, transient ischemic events, angina, and renal disease  . In young patients, if there is no suspicion of atherosclerotic events, other etiologies like vasculitis, hemoglobinopathies, myeloproliferative disorders, hypercoagulable conditions, and the use of oral contraceptives should be excluded .
After confirming the diagnosis of RAO, carotid Doppler ultrasonography and echocardiography are performed to locate the source of the embolus and to prevent further embolization. An electrocardiogram (ECG) is ordered to detect atrial fibrillation and a 24-hour Holter monitoring may be indicated in patients with suspected arrhythmia. Laboratory tests are useful to diagnose the etiology and may include complete blood count, erythrocyte sedimentation rate (ESR), fibrinogen levels, antiphospholipid antibodies, activated partial thromboplastin time (aPTT), prothrombin time (PT), lipid panel, blood culture, and work up to exclude sickle cell disease.
Imaging studies such as echocardiography or carotid Doppler ultrasonography are performed urgently while magnetic resonance angiography (MRA) and computed tomography (CT) angiography can be performed later to detect atherosclerotic disease.
Other ECG Findings
- Ischemic Changes
In all cases, initial OCTA images revealed typical ischemic changes in superficial and deep retinal capillary plexuses. Follow-up OCTA revealed increasing areas of ischemia in the RAO region and persistent narrowing of the arteries. [ncbi.nlm.nih.gov]
General Pathology Histopathological changes following BRAO occur due to ischemic changes in the retinal tissue. These ischemic changes may be seen in the corresponding retinal quadrant, depending on which vessel is occluded. [eyewiki.org]
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