In 1859, Van Graefe first described central retinal artery occlusion (CRAO) as an embolic event to the central retinal artery in a patient with endocarditis. In 1868, Mauthner suggested that spasmodic contractions could lead to retinal artery occlusion. There is a multitude of causes of CRAO, but patients typically present with sudden, severe, and painless loss of vision.
Visual loss from CRAO occurs from the loss of blood supply to the inner layer of the retina. The ophthalmic artery is the first branch of the internal carotid artery and enters the orbit underneath the optic nerve through the optic canal. The central retinal artery is the first intraorbital branch of the ophthalmic artery, which enters the optic nerve 8-15 mm behind the globe to supply the retina. Short posterior ciliary arteries branch distally from the ophthalmic artery and supply the choroid. Anatomical variants include cilioretinal branches from the short posterior ciliary artery, which gives additional supply to the macula from the choroidal circulation. A cilioretinal artery occurs in approximately 14% of the population.
Acutely, obstruction of the central retinal artery results in inner layer edema and pyknosis of the ganglion cell nuclei. Ischemic necrosis results, and the retina becomes opacified and yellow-white in appearance. The opacity is most dense in the posterior pole as a result of the increased thickness of the nerve fiber layer and ganglion cells in this region. Furthermore, the foveola assumes a cherry-red spot because of a combination of 2 factors: (1) the intact retinal pigment epithelium and choroid underlying the fovea, and (2) the foveolar retina is nourished by the choriocapillaris. The late stage shows a homogenous scar replacing the inner layer of the retina.
Approximately 14% of the general population has cilioretinal arteries and 25% of eyes with acute CRAO have cilioretinal artery. The cilioretinal artery supplies part or all of papillomacular bundle. In 10% of eyes, the cilioretinal artery supplies some or all of the foveola. In such an eye, the visual acuity generally returns to 20/50 or better in 80% of eyes over a 2-week period.
The opacification takes as little as 15 minutes to several hours before becoming evident and resolves in 4-6 weeks. The resulting anatomy reflects a catastrophic insult to the inner retinal layers with attenuated retinal arterioles and optic nerve pallor. Pigmentary changes are typically absent since the retinal pigment epithelium remains unaffected. Boxcar appearance of the blood column can be seen in both arteries and veins. Hayreh has shown that irreversible cell injury occurs after 90-100 minutes of total CRAO in the primate model.  Controversy exists regarding the optimal window of treatment in humans, but the conservative approach involves treatment up to 24 hours.
CRAO is found in 1 per 10,000 outpatient visits. Of these patients, 1-2% present with bilateral involvement.
Patients with visualized retinal artery emboli, whether or not obstruction is present, have a 56% mortality rate over 9 years, compared to 27% for an age-matched population without retinal artery emboli. Life expectancy of patients with CRAO is 5.5 years compared to 15.4 years for an age-matched population without CRAO.
Men are affected slightly more frequently than women.
The mean age of presentation is in the early 60s, although a few cases have been reported in patients younger than 30 years. The etiology of occlusion changes depending on the age of presentation.
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