Retinal Artery Occlusion
Occlusion (usually embolic, but can be thrombotic, inflammatory or traumatic) of the bloodflow in the retinal blood vessel. The main artery supplying the eyeball is called the ophthalmic artery. The part of the ophthalmic artery that enters the eye at the optic nerve is called the central retinal artery (CRAO). This artery then divides into a superior and an inferior branch retinal artery that each then further subdivides to supply retinal vessels to the retina.
Atherosclerosis, cardiac (valvular, myxoma) disease and other disorders contributing to embolus formation; coagulopathies (sickle cell, oral contraceptives, homocystinuria, pregnancy, platelet and factor abnormalities), collagen vascular diseases, ocular abnormalities (arterial loops, optic disc drusen) and other (migraine, hypotension, trauma). Most patients are in their 60’s; more men than women are affected. Only 1-2 % are bilateral.
Obstruction of the retinal vascular lumen by an embolus, thrombus or inflammatory/ traumatic vessel wall damage or spasm.
Occlusion of the bloodflow results in severe loss of vision due to oxygen starvation of the retinal tissues and eventual cell death. Irreversible loss occurs within 90 minutes. If treated in time, sometimes, visual loss can be limited. The area of retina affected is associated with the area and degree of visual loss. The most severe is occlusion of the ophthalmic artery. This results in very severe loss of vision (cannot see eye chart, light perception or hand motions).
Control of associated risk factors.
Patients usually complain of the acute onset of visual loss. Patients with central retinal artery occlusion (CRAO) complain of visual loss over the entire field of vision. Patients with a branch retinal artery occlusion (BRAO) complain of focal loss of their field of vision. The loss of vision is usually painless. An exception to the severe loss of vision with central retinal artery occlusion occurs in the presence of a macular cilioretinal artery (about 30% of eyes). In this situation, the central retina (macula) is supplied by a blood source independent of the central retinal artery (a posterior ciliary artery branch) and central acuity may be more normal. Visual loss may have been preceded by transient loss of vision in the past (amaurosis fugax) in the case of embolic sources.
Physical examination and signs
Occlusion of the central retina artery (CRAO) results in an afferent papillary defect and limitation of central acuity (counts fingers level acutely). If there is sparing of the cilioretinal artery, the visual acuity can be significantly better (25 % of CRAOs).
Retinal examination during the acute phases shows slowed/ sludge-like blood flow (can see individual red blood cells moving very slowly as a segmented column) within the occluded vessel. The affected portion of the retina (ischemic) will appear white (retinal ganglion cells swell due to ischemia). In the case of a central retinal artery occlusion, the foveal center (center of the macula) appears red (called a cherry red spot). This is because there are no ganglion cells there and thus any swelling to obscure the underlying RPE and choroidal colors. The whitening of the retina generally lasts 4-6 weeks. The cilioretinal artery can also become occluded; usually has a good prognosis. In the case of patients with a cilioretinal artery, central acuity may be spared despite a retinal artery occlusion and there is no whitening of the retina supplied by the cilioretinal artery.
Chronic signs include thinned retinal vessels, retinal pigment epithelial mottling. In the case of BRAOs, there may be artery-to-artery anastomoses.
Acutely, diagnosis is prompted by the sudden onset of visual acuity loss and the presence of retinal whitening. There is a corresponding field defect. The affected blood vessel shows sluggish bloodflow (boxcarring of the blood column). There may be a refractile lesion within the blood vessel (Hollenhorst plaque), a whitish lesion within a section of the blood vessel (platelet fibrin thrombus) or large calcific plaque (cardiac valvular disease). The arteries are thinned. Veins may be thinned, slightly dilated or normal.
Poor perfusion of the arterial tree can be demonstrated by the ability to induce retinal pulsations in the central retinal artery by digital pressure on the eyeball.
Fluorescein angiography is not necessary. However, if performed, one will see a delay in the filling of the retinal arteries and a delayed arteriovenous transit time in the affected areas. Complete lack of filling of the retinal vessels is very rare. Delayed choroidal filling should point to an ophthalmic or carotid artery obstruction. Over time, the vessels re-open and flow reverts to normal, despite the persistence of retinal vessel narrowing.
Electroretinography, ERG, shows a characteristic diminution of the b-wave. This is due to inner retinal ischemia. The ERG may be normal in some cases (despite poor visual acuity) if the blood flow renormalizes.
A carotid ultrasound duplex scan to determine whether there are carotid plaques present. Cardiac echocardiography is also useful to look for sources of emboli: valvular disease or atrial myxoma (rare).
A sedimentation rate (ESR) and a temporal artery biopsy may be useful in older patients in whom the degree of suspicion is high for giant cell arteritis (GCA).
Blood tests should be performed to rule out associated diseases and causative conditions (see risk factors section).
Sectoral whitening in the path of a branch retinal artery is path gnomic for a BRAO.
A cherry red spot can also be caused by carbon monoxide poisoning.
Neovascularization of the retina (NVD/ NVE) or iris (NVI) is rare complication seen after a CRAO or BRAO. In eyes with NVD/E/I, other causes such as diabetic retinopathy, retinal vein occlusion, retinal vasculitis, sarcoidosis, ocular ischemic syndrome, sickle cell retinopathy should be considered. Of course, the patient’s history will help as will the other ocular findings associated with those other conditions.
NVI from vein occlusions, ocular ischemia.
Medical work-up is indicated. In the case of embolic sources, the mortality rate is 56 % over 9 years versus an age-matched rate of 27 %.
Medical therapy and follow up
Acute treatment to limit visual acuity loss is usually effective within 90 minutes of onset. A patient should be instructed to breathe into a bag -increases carbon dioxide content which causes vasodilation- until he/she can be seen by an ophthalmologist. In the office, a paracentesis (removal of fluid from the anterior chamber- space between cornea and iris- using a small gauge needle (27 or 30 gauge) attached to a tuberculin syringe) can be used to remove 0.1 to 0.4 ml of aqueous fluid within the first 24 hours. A paracentesis lowers the intraocular pressure and may allow the embolus (if any) to move further down the vessel and away from the central retina (limits extent of damaged retina). In addition, the intraocular pressure may be decreased medically with eyedrops. If available, a mixture of 95 % oxygen and 5 % carbon dioxide can be used to increase bloodflow.
Patients should be evaluated by an internist, who should be instructed to look for the associated conditions.
Surgery and Surgical follow up
Neovascularization of the iris, retina or angle.
Visual loss with CRAO is usually severe. However, with CRAOs, in the presence of a cilioretinal artery, visual acuity usually recovers to 20/50 or better in over 80 % of eyes. NVI may occur in 15-20 %. Patients need to be examined for development of iris neovascularization, which has been reported to occur from 2.5 % to 31.6 % of patients. A recent study showed an prevalence of 18 % with a mean onset of 8.5 weeks post-occlusion.
Visual field loss in BRAOs is usually permanent. Visual acuity may recover to 20/40 or better in 80 % of eyes.
Atebara NH, Brown GC, Cater J. Efficacy of anterior chamber paracentesis and Carbogen in treating nonarteritic central retinal arterial occlusion. Am J Ophthalmol 1995; 102:2029-2034.
Augsburger JJ, Magargal LE. Visual prognosis following treatment of acute retinal artery obstruction. Br J Ophthalmol 1980; 64:913-917.
Brown GC, and Magargal LE. Central retinal obstruction and visual acuity. Ophthalmology 1982;89:14-19.
Brown GC,and Shields JA. Cilioretinal arteries and retinal artery occlusion. Arch Ophthalmol 1979;97:84-92.
Brown GC, Magargal LE, Shields JA, Goldberg RE and Walsh PN. Retinal artery obstruction in children and adults. Ophthalmology 1981;88:18-25.
Duker JS, Brown GC. Neovascularization of the optic disc associated with obstruction of the central retinal artery. Ophthalmology 1989; 96:87-91.
Frayser R, Hickham JB. Retinal vascular response to breathing increased carbon dioxide and oxygen concentrations. Invest Ophthalmol 1964;3:427-431.
Gold D. Retinal arterial occlusion. Trans Am Acad Ophthalmol Otolaryngol 1977; 83:392-408.
Hayreh S and Podhajsky P. Ocular neovascularization with retinal vascular occlusion, II. Occurrence in central and branch retinal artery occlusion. Arch Ophthalmol 1982;100:1585-96.
Hayreh SS, Kolder HE, Weingeist TA. Central retinal artery occlusion and retinal tolerance time. Ophthalmology 1980; 87:75-78.
Perraut LE, Zimmerman LE. The occurrence of glaucoma following occlusion of the central retinal artery. A clinicopathologic report of six cases with a review of the literature. Arch Ophthalmol 1959; 61:845-865.
Recchia FM, Brown GC. Systemic disorders associated with retinal vascular occlusion. Curr Opin Ophthalmol 2000; 11:462-467.
Rudkin AK, Lee AW, Chen CS. Ocular neovascularization following central retinal artery occlusion: prevalence and timing of onset. Eur J Ophthalmol 2010 May 28 Epub.
Savino PJ, Glaser JS, Cassady J. Retinal stroke: Is the patient at risk? Arch Ophthalmol 1977;95:1185-89.
Sharma S, Grown GC, Cruess AF for the RECO Study Group. The accuracy of visible retinal emboli for the detection of cardio-embolic lesions requiring anticoagulation or cardiac surgery. Br J Ophthalmol 1998; 82:655-658.
Sharma S, Pater JL, Lam M, Cruess AF. Can different types of retinal emboli be reliably differentiated from one another? An inter- and intraobserver agreement study. Can J Ophthalmol 1998; 33:144-148.
Silberberg DH, Laties AM. Occlusive migraine. Trans Pa Acad Ophthalmol Otolaryngol 1974; 27:34-38.
Jennifer I Lim MD