associated with stenosis of the ipsilateral ophthalmic artery [24].

Pain

Pain is present in the affected eye or orbital region in about 40% of OIS cases [5]. We have referred to this pain as “ocular angina” [5]. Most often, it is described as an intermittent dull ache. Neovascular glaucoma can be the cause, although in those eyes with normal intraocular pressure, the cause may be ischemia to the globe and/or ipsilateral dura.

Visual Acuity

The presenting visual acuities of eyes with the OIS are bimodally distributed, with 43% of affected eyes having vision ranging from 20/20 to 20/50 and 37% having counting fingers or worse vision [25]. Absence of light perception is generally not seen early but can occur in the later stages of the disease, usually secondary to neovascular glaucoma. Among all eyes, treated and untreated, with the OIS at the end of 1 year of follow-up, 24% remain in the 20/20–20/50 group, while a large 58% have counting fingers or worse.

Signs

External

A prominent superficial temporal artery can occasionally be seen with the OIS (Fig. 24.3). This vessel is typically a collateral artery that allows blood flow from the ipsilateral external carotid system to pass across the midline and supply an occluded, contralateral, carotid arterial system. Giant cell arteritis can also cause an enlarged superficial temporal artery, although it is typically tender and irregular, while that associated with the OIS is not. Caution should be exercised if an enlarged superficial temporal artery is encountered with OIS symptoms and signs since

Fig. 24.3 A prominent superficial temporal artery in a patient with the ocular ischemic syndrome with a 100% left common carotid obstruction. Blood from this vessel crosses over to supply the left carotid arterial system

a temporal artery biopsy to confirm giant cell arteritis could suddenly interrupt blood flow to the contralateral brain and result in a cerebrovascular accident.

Anterior Segment Changes

Unfortunately, neovascularization of the iris is already seen in approximately two-thirds of eyes with the OIS at the time of presentation (Fig. 24.4a, b) [5]. This finding is associated with a 90% incidence of counting fingers vision at 1 year [25]. Nevertheless, only half of these eyes have or develop increased intraocular pressure, even if the anterior chamber angle is closed by fibrovascular tissue [5]. Impaired ciliary body perfusion, with a subsequent decrease in aqueous production, likely accounts for this phenomenon.

Flare in the anterior chamber is present in most eyes with iris neovascularization. An anterior chamber cellular response is seen in about one-fifth of eyes with the OIS [5] but rarely exceeds grade 2 using the Schlaegel classification [26]. Keratic precipitates can be present but are unusual.

In unilateral cases, there is generally little difference between the degree of cataractous lens change in each eye. As the disease progresses, however, cataractous changes can develop. In advanced cases, the lens may become mature.

Posterior Segment Findings

The retinal arteries are usually narrowed in OIS eyes, while the retinal veins are most often dilated but not tortuous (Fig. 24.5) [5]. The venous dilation may be accompanied by beading but usually not to the extent seen in eyes with marked preproliferative or proliferative diabetic retinopathy. Dilation of the veins seems to be a nonspecific response to ischemia in the OIS, diabetic retinopathy, threshold retinopathy of prematurity, and other vasculopathies.

In contrast to OIS eyes, those with central retinal vein obstruction usually have generally dilated veins that are also tortuous. The fact that the OIS occurs secondary to impaired inflow, while a central retinal vein obstruction is associated with compromised outflow from thrombus formation at or near the lamina cribrosa [27], differentiates the ocular response to inflow and outflow vasculopathies.

Retinal hemorrhages are seen in about 80% of affected eyes. They are most commonly seen in the mid-periphery (Fig. 24.6) but can also extend into the posterior pole. While dot and blot hemorrhages are the most common variant, superficial retinal hemorrhages in the nerve fiber layer are occasionally seen. The hemorrhages likely arise secondary to leakage from the smaller retinal vessels with endothelial damage secondary to ischemia. Similar to the case with diabetic retinopathy, these hemorrhages may also result from

Fig. 24.5 Posterior pole of the right fundus of an ocular ischemic syndrome in a patient with a 100% internal carotid occlusion. The retinal arteries are narrowed and the retinal veins are dilated and slightly beaded, but the tortuosity seen with outflow occlusions, such as central retinal vein occlusion, is absent

the rupture of microaneurysms. In general, the hemorrhages seen with the ocular ischemic syndrome are considerably less numerous than those accompanying central retinal vein obstruction. They are virtually never confluent in OIS eyes.

Microaneurysms are frequently observed outside the posterior pole but can be seen in the macular region as well. Hyperfluorescence with fluorescein angiography (Fig. 24.7a, b) differentiates these abnormalities from hypofluorescent retinal hemorrhages. Retinal telangiectasia has also been described [28].

Fig. 24.6 (a) Dot and blot hemorrhages in the midperipheral fundus of a patient with the ocular ischemic syndrome. (b) Histopathologic correlate of dot and blot hemorrhages in association with the ocular ischemic syndrome. Blood, typically present in the inner nuclear/outer plexiform layer, has spread through almost the full thickness of the retina (Fig. 24.6b Hematoxylin-eosin ×100; courtesy of Dr. W. Richard Green)

Posterior segment neovascularization can occur on the optic disk (Figs. 24.8 and 24.9) and/ or on the retina (Figs. 24.10 and 24.11). Neovascularization of the disk is encountered in about 35% of eyes, while neovascularization of the retina is seen in about 8% [5]. Vitreous hemorrhage arising from traction upon the neovascularization by the vitreous gel (Fig. 24.9) has been reported to occur in 4% of eyes with the ocular ischemic syndrome in a retrospective study [5]. Rarely, the neovascularization can progress to severe preretinal fibrovascular proliferation.

A cherry-red spot characteristic of acute central retinal occlusion is seen in approximately 12% of eyes with the OIS [5]. It can occur secondary to inner layer retinal ischemia from embolic obstruction or hemorrhage under an atherosclerotic plaque in the central retinal artery. Nonetheless, it probably develops more often when the intraocular pressure exceeds the perfusion pressure within the central retinal artery, especially in eyes with neovascular glaucoma. When iris neovascularization develops several weeks after central retinal artery obstruction, severe carotid artery obstruction may or may not be present. When iris neovascularization is present, however, at time of presentation of a central retinal artery obstruction, a severe obstruction of the ipsilateral carotid arterial system should be suspected.

Fig. 24.7 (a) Positive intravenous fluorescein angiogram in an ocular ischemic syndrome eye at 4.5 min after injection shows multiple small hyperfluorescent dots corresponding to microaneurysms in the mid-peripheral

retina. (b) Histopathologic correlation of a large microaneurysm (MA) from an eye with the ocular ischemic syndrome (Fig. 24.7b Hematoxylin-eosin ×100; courtesy of Dr. W. Richard Green)