Central Retinal Artery Occlusion (CRAO)

Introduction

• Opthalmological Emergency

• Complete vision loss in one eye

• Analoguous to Acute Ischemic Stroke

Epidemiology

• Occurs in an estimated 1 in 100,000 people

• Occurs in 1.90 per 100,000 in the United States white population

• Accounts for 1 in 10,000 ophthalmologic outdoor visits

• 80% of patients have a visual acuity of 20/400 or worse

• Incidence in men is 1.47 times higher than in women

• <2% patients present with bilateral involvement

• Mean age of presentation is early 60s

Anatomy

• Central retinal artery originates from the intra-orbital part of the ophthalmic artery which is the first branch of internal carotid artery

• Arises medial to the ciliary ganglion

• Usually, the first branch of the ophthalmic artery (67%), may present as a second branch (28%)

• Follows a tortuous path inside the orbital cavity

• Enters optic sheath 18.6 mm from the distal end of the optic canal, 8.0 mm behind the posterior pole of the globe

• Penetrates lower surface of the dura matter in an oblique manner 1 cm behind the eyeball on the inferomedial side of the optic nerve

• Courses through the meninges and crosses the cranial nerve to be located in its center

• Reaches the optical papilla where it divides to give branches

• Cilioretinal artery is present in 49.5% of patients and it supplies the papillomacular bundle

Figure 1: Ophthalmic artery and its branches

Microsurgical Anatomy

• Has narrowing at the level of the dural sheath and at the level of the cribriform plate

• Distance Between the dural perforation point of the Central retinal artery and the optic disc is 8.36 mm

• The average diameter is 0.4 mm

Figure 2: Cilioretinal retinal artery

Risk Factors

• Hypertension

• Hyperlipidemia

• Smoking

• Diabetes Mellitus

• Hyperhomocysteinemia

• Family history of vascular disease

• Use of cocaine

• Polycythemia vera

• Vasculitis

• Thrombophilia

• Sickle cell anemia

• Multiple myeloma

• Systemic lupus erythematosus

• Prothrombin III mutation

• Giant Cell Arteritis

• Intravitreal Injection of VEGF Therapy

• Orbital or Head Injuries

Types of Central Retinal Artery Occlusion

1. Non-arteritic permanent CRAO

• This accounts for >2/3rd of cases of CRAO.

• Non-arteritic permanent CRAO occurs when a thrombus or embolus, as a result of atherosclerotic disease, blocks the central retinal artery.

2. Non-arteritic transient CRAO

• This accounts for 15–17% of cases of CRAO.

• According to a proposed mechanism, transient vasospasm occurs due to serotonin release from platelets on atherosclerotic plaque. This vasospasm is reversible hence this form of CRAO has the best prognosis.

3. Non-arteritic CRAO with cilioretinal sparing

• Preserved perfusion of the macula by the cilioretinal artery, which is present in 49.5% of the population, results in macular sparing.

4. Arteritic CRAO

• This accounts for 4.5-5% of cases of CRAO.

• This is caused by vasculitides, which in almost all cases is Giant Cell Arteritis.

Pathophysiology

• Most common cause: Thromboembolic
• Central retinal artery occlusion is embolism formed due to atherosclerotic plaques derived from carotid artery
• Cholesterol (74%)
• Fibrin (15.5%) and
• Calcific material (10.5%)

• Most common Artertic Process: Giant Cell Arteritis. GCA causes nodular granulomatous inflammation of medium and large sized arteries leading to the development of a fragmented internal elastic lamina and FFA in patients show occlusion of posterior ciliary artery which supply the optic nerve head and cilio-retinal arteries resulting in arteritic anterior ischemic neuropathy

• Occlusion of central retinal artery leads to hypoperfusion of retina, retinal cell damage and eventually necrosis

• Central retinal artery occlusion of about 240 minutes results in irreversible retinal damage

• Other less common sources of emboli include
• Tumor emboli from cardiac myxoma
• Fat emboli from bone fractures
• Bacterial endocarditis induced emboli and
• Septicemia induced septic emboli

• Thrombi due to atherosclerotic disease, collagen-vascular diseases, inflammatory or hypercoagulable diseases can cause central retinal artery occlusion

• Other causes of occlusion include a foreign body, migraine, spasm of the central retinal artery, or encephalitis

Clinical Presentation

Clinical Features

• Presents as a transient , painless monocular vision loss (amaurosis fugax) and an afferent pupillary defect

• May be preceded by transient visual obscurations ( migrating embolism or giant cell arteritis )

• May complain of a purplish hue to the blur

• May complain of hallucinations

• Simultaneous onset of CRAO in both eyes is rare

• Central vision may be preserved if cilioretinal artery is present

• Visual acuity may vary from loss of light perception to finger counting

Figure 3: Cherry red spot , retinal edema and vessel attenuation visible in CRAO

Ocular Evaluation in different types of CRAO

Visual Field Defects In Central retinal Artery Occlusion

• Temporal island (59%)

• Central and centrocecal scotoma (19%)

• Complete blindness (10%)

• Peripheral constriction (8%)

• Paracentral scotoma (3%)

Differential Diagnosis

• Retinal vein occlusion

• Retinal detachment

• Giant cell arteritis

• Multiple sclerosis

• Acute angle-closure glaucoma

• Papilledema

• Globe rupture

• Sickle cell anemia

• Epilepsy

Investigations

• Complete blood count and coagulation assays (PT/INR, PTT)

• ESR and CRP (more reliable) levels to rule out giant cell arteritis

• CT head without contrast to rule out intracranial hemorrhage

• Fluorescein angiography for the presence of posterior ciliary artery occlusion

• Trans esophageal echocardiography to evaluate heart lesions which can be a source of emboli

• Lipid profile(LDLs should be not more than 70s mg/dL)

• Thrombophilia evaluation by a thrombophilia screen

• Consider intravenous fluorescein angiography to confirm the diagnosis

Management

• Distinguish complete from incomplete CRAO to identify patients that might benefit from treatment

• Advise the patient to have a low-fat diet rich in fruits, vegetables, fish and lean meats for secondary prevention

Lower IOP

• Perform an emergency anterior chamber paracentesis

• Perform ocular massage using a three-mirror contact lens by compressing the gobe for 10 seconds followed by a 5 second release or over closed eyelids for 15–20 minutes

• Treat with intravenous mannitol 1.5–2 g/ Kg over 30–60 min . Contraindicated if the patient is hypersensitive, severely dehydrated, or has progressive renal disease

• Inject Intravenous acetazolamide 500 stat / 250 mg every 4 hours for 24 h . Contraindicated if the patient is hypokalemic , hyponatremic and suffers from a sulfa allergy or liver, renal disease

• Treat with timolol 0.25% ophthalmic solution 1 gtt every 12 hours . If it is not effective then increase to 0.5% 1 gtt every 12 hours

Vasodilators

• Treat with Pentoxifylline 600 mg TDS (vasodilator) if the patient is not allergic to theophylline or caffeine

• Start hyperbaric oxygen 2–2.5 atm for 90 min within 8 hours of onset

• Treat with sublingual isosorbide dinitrate 10 mg. Contraindicated if patient is hypersensitive, anemic or has a recent use of phosphodiesterase inhibitors

• Start carbogen inhalation for 10 min per hour when awake and 10 min every 4 hours at night. Continue for 48–72 hours

Reduce Retinal Edema

• Treat with a single dose of 1g intravenous methylprednisolone. Not recommended for non-arteritic permanent CRAO

Dislodge the Clot

• Use Nd YAG laser 0.8–1.1 mJ intensity focused on arterial wall behind embolus to dislodge the embolus

• Perform a pars plana vitrectomy followed by embolus removal

Embolus Thrombolysis

• Administer intra arterial continuous infusion of tPA 40–80 mg or urokinase in a dose range of 300,000 to 1 million units . Contraindicated if patient has an evidence of intracerebral hemorrhage, a suspicion of subarachnoid hemorrhage, myocardial infarction, intracranial or intraspinal surgery , serious head trauma or stroke in the last 3 months , gastrointestinal or genitourinary hemorrhage in the previous 3 weeks, a history of intracerebral hemorrhage and uncontrolled hypertension at time of treatment or a blood glucose >22.22 mmol

• Perform follow-up ophthalmic examination 1-4 weeks after the event to check for neovascularization

Factors Which Influence the Visual Outcome

Site of Occlusion Of Central Retinal Artery

• Determines the amount of residual retinal circulation

Dural sheath

• Pial and intraneural collaterals are intact and establish residual retinal circulation

Lamina cribrosa

• No collaterals present to establish retinal circulation

Causes of Occlusion

• Giant cell arteritis involves the posterior ciliary artery

• When the common trunk is occluded , both arteries are occluded which is characteristic of arteritic CRAO but rare in NA-CRAO

• The combined occlusion has a much worse visual loss than in NA-CRAO

Length of CRAO

• Central retinal artery occlusion of upto 97 min has no detectable damage

• Central retinal artery occlusion of about 240 minutes results in irreversible retinal damage

• Increased duration of ischemia results in increased duration before any improvement of function occurs after circulation is restored

Patent Cilioretinal Artery

• If it supplies the foveal region, visual acuity is almost always normal

• If its supply just reaches the foveola , there is an initial marked fall of visual acuity but it improves markedly within 2–3 weeks

• If it supplies a small peripapillary region , a small visual field is present with poor visual acuity

Conclusion

• Although an accepted evidence-based therapy for CRAO does not exist , a quick diagnosis , ruling out giant cell arteritis and management to prevent further end-organ ischaemia within 6 hours of onset of symptoms must be done pending future management guidelines

Further Reading

• Argyrios Chronopoulos, James S. Schutz, Central retinal artery occlusion—A new, provisional treatment approach, Survey of Ophthalmology, Volume 64, Issue 4, 2019

• Dumitrascu, Oana M. MD, MSc; Newman, Nancy J. MD; Biousse, Valérie MD Thrombolysis for Central Retinal Artery Occlusion in 2020: Time Is Vision!, Journal of Neuro-Ophthalmology: September 2020 - Volume 40 - Issue 3 - p 333-345 doi: 10.1097/WNO.0000000000001027

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