CHAPTER 46 RETINAL ARTERIAL OBSTRUCTION 369
15.How do you tell a retinal arterial obstruction from a retinal venous obstruction?
It is simple—white versus red. The hallmark of retinal arterial obstructions is ischemic retinal whitening. The hallmark of retinal venous obstruction is retinal hemorrhage in the territory of the obstructed vessel. In addition, the retinal veins will appear dilated and tortuous as opposed to thin and attenuated.
Warning: Rarely, a patient may present with a combined obstruction. Obstructions of a branch retinal artery or the central retinal artery in conjunction with a central retinal venous obstruction have been reported. This produces a combined fundus picture (i.e., whitening from ischemia with red from retinal hemorrhage).
16.Is acute obstruction of a retinal artery an emergency?
CRAO is considered a true ophthalmic emergency, even though there is no proven treatment. Because the retina is highly sensitive to ischemia, treatment should be initiated as quickly as possible if contemplated. Although animal studies indicate that more than 90 minutes of ischemia produce irreversible retinal cell death, clinical experience suggests that some eyes can tolerate ischemia for up to 72 hours and still recover. If a potentially risky intervention such as anticoagulation is contemplated, the visual loss should be no more than 48 hours old to maximize the possibility of recovery and the overall risk-to-benefit ratio. Optimal timing for anticoagulation is within 6 to 8 hours of visual loss. In addition, concurrent systemic diseases need to be ruled out.
17.What does the retina look like months or years after an arterial obstruction?
The retinal vessels look attenuated and the optic disc is often pale, owing to the loss of the retinal nerve fiber layer. Because the retina itself is transparent and the underlying retinal pigment epithelium and choroid are unaffected by a pure CRAO or BRAO, the retina itself looks normal.
18.Are there any other late complications after retinal arterial obstructions?
Neovascularization of the iris occurs in approximately 15% of patients with CRAO. It is usually seen within 3 months of the CRAO and can result in a severe type of glaucoma called neovascular glaucoma (NVI). If NVI is detected, a laser treatment to the ischemic retina, panretinal photocoagulation, is usually performed. Neovascularization is extremely rare after BRAO.
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