branch retinal artery occlusion (Fig. 7.22). These cases have led to the broader terminology of patchy ischemic retinal whitening.14

Approximately 4% of CRVOs have associated cilioretinal arteriolar insufÞciency (CRAI) (Fig. 7.14).51 Many of these cases occur in patients with nonischemic CRVOs in patients under age 50 without hypertension and often with relatively low blood pressure.46,51,90,143,147 The mean age of the 21 patients with CRAI in two case series was 54.2±SD17.0 compared to a mean age for CRVO in general of 61.8±SD16.5 in a case series of 612 CRVOs (P=0.0385, unpaired T test).13,60,91 The proportion of cases of CRVO with CRAI that are nonischemic is higher than the proportion of nonischemic CRVOs in general.51 If rapid-sequence frames are taken in the ßuorescein angiogram during the early phase, it is often possible to see the cilioretinal arteries in these cases Þlling before the retinal arteries and demonstrating pulsatile blood ßow and intermittent retrograde ßow, implying that the increased venous pressure associated with the CRVO is imposing hypoperfusion on the region of the retina supplied by the cilioretinal artery.48,51,99

Visual acuity outcomes are often excellent in patients with CRAI. They need not have absolute or any scotomata in the area of the cilioretinal arteriolar whitening indicating that these need not be infarctions, though they have been termed such.51,69 Cilioretinal arteriolar insufÞciency may be a more accurate term for the clinical phenom-

ena.51,143 When scotomata are present upon diagnosis, they usually diminish in size and elevation of threshold with follow-up.13,51 Many patients with CRVO or HCRVO with cilioretinal arteries donotdevelopcilioretinalarteriolarinsufÞciency.51 It is important to distinguish this syndrome from combined CRVO and central retinal artery occlusion because they have different prognoses; visual outcome in the latter is much worse.111

Mcleod has contended that CRAI in CRVO is not due to increased cilioretinal arteriolar resistance to ßow either due to the Bayliss effect or due to an excessively high vasomotor tone of cilioretinal arterioles.91 Instead, he hypothesized that an unusually distal origin of the posterior ciliary artery along the ophthalmic artery (which would lower its pressure relative to that of a more proximally offshooting central retinal artery) or partial arteriolar narrowing of the posterior ciliary arteries from atherosclerosis might plausibly explain the pathophysiology.91 Others have suggested local arteriolar vasospasm of the cilioretinal artery.20

High-grade obstruction of the central retinal vein can cause central retinal artery insufÞciency as well, along with ischemic retinal whitening of the macula similar to that seen with central retinal artery occlusion. Although these cases are often called combined central retinal artery and vein occlusions, they can be entirely explained as a consequence of high-grade central vein occlusion (see Fig. 2.24).120