Branch Retinal Artery Occlusion
Branch retinal artery occlusion describes decreased arterial blood flow to the retina leading to ischemic damage. The severity of visual loss depends upon the area of retinal tissue affected by the vascular occlusion.
ICD 9 Codes
- 362.32 Retinal arterial branch occlusion
- 362.33 Partial retinal arterial occlusion
- 362.34 Transient retinal arterial occlusion
- H34.23 Retinal artery branch occlusion
- H34.231 Retinal artery branch occlusion, right eye
- H34.232 Retinal artery branch occlusion, left eye
- H34.233 Retinal artery branch occlusion, bilateral
- H34.234 Retinal artery branch occlusion, unspecified eye
Branch retinal artery occlusion (BRAO), a common disorder of the ocular vasculature, stems from the occlusion of a branch of the central retinal artery. BRAO represent 38% of all acute retinal artery obstructions. The resultant hypoperfusion of retinal tissue may result in vision loss. While frequently described under one heading, two distinct subtypes comprise the condition: permanent BRAO and transient BRAO . More permanent occlusion typically results in more severe visual losses. Transient BRAO bears a better visual prognosis.
Any condition which causes decreased perfusion in a branch retinal artery can result in BRAO. Typically, this hypoperfusion results from emboli to a branch of the central retinal artery. On funduscopic examination, emboli are visualized in 62% of cases. They often occur at the bifurcation of vessels, and the temporal retinal arteries are involved in 98% of cases . The embolus may be composes of cholesterol or fibrin. Other less common forms of embolic sources include calcified cardiac valves, fat emboli from long bone fractures, air emboli from trauma or surgery, talc emboli from IV drug use and synthetic emboli from interventional procedures.
Nonembolic causes of BRAO include vasospasm secondary to migraines, cocaine abuse and sildenafil, vasculitidies such as Behcets Disease, coagulopathies, and inflammatory/infectious conditions such as Toxoplasmosis, Herpes Zoster, Lyme disease and Giant Cell Arteritis. Susac syndrome is a rare disease with clinical features including encephalopathy, sensorineural hearing loss, and BRAO. This particular cause of BRAO possesses an auto-immune etiology, with antiendothelial cell antibodies playing an important role. Endothelial cell injury, the accumulation of thrombotic material, and narrowing of the vessel lumen is thought to result in BRAO.
BRAO has been reported to occur following retrobulbar anesthesia for intraocular sugery. Acute vasoocclusion occurred following the administration of mepivacaine which contained the preservatives methyl- and propyl para-hydroxybenzoate at a tenfold higher rate when compared to those anesthetized with preservative-free mepivacaine. Some vasospasm, whether from trauma, compression, or a reaction to the anesthetic was suggested as a possible explanation.
Risk factors for BRAO include systemic conditions which preclude an individual towards vascular narrowing: hypertension, carotid occlusive disease or atherosclerosis, coronary artery disease, and hypercholesterolemia. Diabetes mellitus and transient ischemic attack/cerebrovascular accident occur more frequently in patients with BRAO compared to the general US population. Smoking has been associated with BRAO as well. BRAO more commonly occurs in elderly patients and is an extremely rare occurrence in pediatric patient populations.
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. Inner retinal edema occurs acutely, with atrophy occurring in more permanent occlusion. In mouse models, at 24 hours following occlusion, Pyknotic nuclei, vauolated spaces, and degenerative changes may be noted by light microscopy in the ganglion cell and inner nuclear layers. Approximately 80% of retinal ganglion cells demonstrate nuclear loss after 21 days.
In response to ischemia, apoptotic cell death of the inner retinal layers occurs following prolonged BRAO. With increasing severity of occlusion, more apoptosis occurs. Several changes in gene expression have been elucidated following retinal artery occlusion in mouse models. T-cell antigen 1 (Thy-1) mRNA levels decrease gradually, suggestive of cellular loss following apoptosis. Additionally, heme oxygenase-1 (HO-1), which responds to the early stages of hypoxia, peaks at 12 or 24 hours after damage to retinal cells.
Given its association with systemic disorders which result in luminal narrowing of blood vessels, primary prevention of BRAO should be aimed at chronic management of conditions such as hypertension, hypercholesterolemia, and diabetes mellitus. Smoking cessation counseling should be offered to prevent BRAO and myriad other medical conditions.
Both central and branch retinal artery occlusions present as an acute onset of painless, monocular visual impairment. BRAO often occurs with a more focal loss of vision, since it only affects a branch of the retinal artery. Presenting visual acuities (VA) differ greatly between BRAO and CRAO. In CRAO, 10.8% of patients present with a VA of 20/40 or better while 74% present with a VA of counting fingers (CF) or worse. In permanent BRAO, 74% of patients present with VA of 20/40 or better; in those with transient BRAO, 94% of patients present with 20/40 or better.
Retinal ischemia is most frequently demonstrated by the presence of cotton wool spots (nerve fiber layer infarcts) and retinal whitening on funduscopic examination. In BRAO, this retinal whitening follows the course of a branch artery. This whitening occurs as a result of intracellular edema and, eventually, apoptosis associated with ischemic changes. A distribution following an arterial branch differentiates this entity from CRAO. Retinal emboli may be observed on funduscopic examination in 62% of cases with the most common site being at a bifurcation where the luminal diameter is narrowest.
Patients present with an acute onset of painless monocular visual loss or visual field loss.
Classical clinical findings consistent with BRAO include the acute onset of monocular visual deterioration. This visual loss is often painless. BRAO should be differentiated from CRAO. Cotton wool spots in the distribution of a branch retinal artery, corroborated by fluorescein angiography, suggest BRAO. Classification of BRAO can also be subdivided by its temporal profile and the particular vessels implicated. BRAO may be described as permanent BRAO, transient BRAO, or cilioretinal artery occlusion (CLRAO), specifically. CLRAO necessitates a unique distinction because its proximal blood supply arises from the posterior ciliary artery (choroidal circulation), not the central retinal artery.
Perfusion of the retinal arteries may be visualized using fluorescein angiography (FA). On FA, plaques within the vessel lumen, a slowly progressive anterior front of the dye, delayed filling, and retinal ischemia may be observed. Spectral domain optical coherence tomography (SD-OCT) may prove useful in identifying retinal edema and atrophy associated with retinal ischemia and comparing these ischemic changes to adjacent, unaffected retinal tissue. In acute phase, the scan through the affected area in BRAO shows increased inner retinal reflectivity and in late phase inner retinal thinning ensues.
Carotid evaluation is imperative when no other etiology is apparent in the elderly and two dimensional or transesphogeal echocardiographic study of the cardiac valves and aorta assist in locating embolic sources of retinal occlusions. MRI of the brain should be ordered when Susac Syndrome is contemplated.
Erythrocyte sedimentation and C reactive protein evaluation are important tests in determining whether central retinal artery occlusion occurs secondary to giant cell arteritis (GCA). Since the cilioretinal artery is a branch of the posterior ciliary artery, CLRAO is the only subdivision of BRAO which can occur secondarily to GCA. Therefore, these tests also assist in determining whether CLRAO alone occurs due to GCA. BRAO, not of the cilioretinal artery, does not typically result from giant cell arteritis (GCA) as described in the paper by Dr Sohan Singh Hayreh. This vasculitis affects medium and large arteries only; the branches of the retinal arteries are arterioles which are too small to be affected by GCA.
The differential diagnosis for sudden onset monocular vision loss includes CRAO, BRAO, ischemic optic neuropathy, and retinal detachment.
The most critical aspect of managing patients with BRAO is to assess their risk of stroke. Accordingly, all patients should undergo examination by an internist with carotid ultrasound and/or echocardiography as needed. Referral to a stroke center is appropriate. BRAO often resolves spontaneously, especially those which are of a transient nature. The literature suggests that the presenting VA with BRAO provides a serviceable indication of visual prognosis. Because prolonged ischemia often produces irreversible damage, and many occurrences of BRAO improve spontaneously, aggressive management in BRAO is not pursued frequently.
- Antiplatelet therapy as needed
- Intravitreal anti-VEGF therapy for neovascular complications.
- Surgical or LASER (Nd-YAG) embolectomy has been tried with variable success. Systemic evaluation is the most important part of management.
- Carotid endarterectomy when indicated
- Laser photocoagulation for neovascular complications.
The most damaging complication of BRAO is neovascularization (NV) in response to the retinal ischemia .
The prognosis of visual improvement following BRAO correlates with the initial presenting visual acuity. In permanent BRAO, findings demonstrate that 74% of patients present initially with a VA of 20/40 or better, and 89% of patients with permanent BRAO present as such on follow-up. In transient BRAO, 94% of patients present initially with a VA of 20/40 or better, and 100% of patients with transient BRAO present as such on follow-up .
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