Introduction
Ocular ischemic syndrome (OIS) encompasses a spectrum of variable signs and symptoms arising from chronic ocular hypoperfusion, usually secondary to severe carotid artery obstruction. Additional names given to this condition include hypoperfusion retinopathy, hypotensive retinopathy, ischemic ocular inflammation, and ischemic oculopathy. In 1963 Kearns and Hollenhorst introduced the term venous stasis retinopathy to first describe findings in patients with advanced carotid artery insufficiency. In order to avoid confusion, this term is best avoided, as it has been used by others when referring to nonischemic central retinal vein occlusion (CRVO), an entirely different condition.
Epidemiology and Pathogenesis
OIS rarely develops before age 50, with a mean age of 65 years at presentation. Men are affected twice as often as women (reflecting the higher incidence of atherosclerotic cardiovascular disease in men) without racial predilection. Bilateral involvement occurs in approximately 20% of cases. The incidence of the syndrome is estimated at 7.5 cases per million population annually, a figure that may be falsely low since the condition can often be clinically mistaken for other vascular diseases.
Approximately 5% of patients who have hemodynamically significant atherosclerotic carotid artery disease develop OIS, with most cases generally showing 90% obstruction of the ipsilateral carotid artery system. Patients with poor collateral circulation between the external and internal carotid systems are susceptible to developing OIS at even lesser degrees of occlusion, whereas those with well-developed collaterals may not develop the syndrome even with total occlusion of the internal carotid artery. Uncommonly, in patients without carotid disease, isolated obstruction of the ipsilateral ophthalmic artery has been reported as a cause for OIS.
The period and extent of the impaired blood flow necessary to develop this syndrome still is not clear. Color Doppler imaging of eyes with OIS has revealed decreased peak systolic flow velocities of the central retinal artery and reversal of flow within the ophthalmic artery. Reversal of the ophthalmic artery flow represents collateralization to the external carotid artery system as a result of obstructions in the internal carotid artery system. This further contributes to hypoperfusion and subsequent ischemia of the optic nerve, choroid, retinal pigment epithelium, and outer segments of the photoreceptors, likely resulting in the visual loss seen in OIS.
Ocular Manifestations
Symptoms
A history of transient vision loss is reported by 10%–15% of patients with OIS. Decreased visual acuity is present in over 90% of affected patients at initial evaluation. Loss of vision generally occurs gradually, over a period of weeks to months, but can occur abruptly. The severity is variable: 35% of affected eyes at the time of evaluation have a visual acuity of 20/40 (6/12) or better; 30% range from 20/50 (6/15) to 20/400 (6/120); in 35%, acuity is sufficient to count fingers or worse. The absence of light perception is an uncommon finding initially but may develop as a sequela of severe posterior segment ischemia frequently in combination with neovascular glaucoma. Varying patterns of visual field loss, positive visual phenomena, and prolonged recovery of vision after exposure to bright lights are also associated symptoms. A dull ache over the eye or brow, referred to by some authors as ocular angina, is reported in up to 40% of patients with OIS and can result from ischemia of the globe or elevated intraocular pressure (IOP) caused by neovascular glaucoma.
Anterior Segment
Anterior segment findings in OIS are common and rarely may be the sole ocular manifestation of carotid occlusive disease. Anterior segment neovascularization in a nondiabetic patient without evidence of venous occlusive disease or other predisposing cause, is suggestive of OIS. Approximately two-thirds of eyes exhibit neovascularization of the iris at initial examination, with neovascular glaucoma seen in half of these eyes. Despite complete angle closure by fibrovascular proliferation, some patients will demonstrate normal IOP due to decreased aqueous humor production as a result of impaired ciliary body perfusion from carotid occlusion. Anterior uveitis in eyes that have OIS has been well described. Iritis, present in 20% of these eyes, is generally mild. Flare is a more prominent feature than the cellular response, and keratitic precipitates are seen infrequently. The possibility of OIS must be considered in patients over 50 years of age who have new-onset iritis. Lens opacification, even formation of a mature cataract, may occur in the end stages of OIS.
Posterior Segment
Posterior segment signs are more frequent than those in the anterior segment and provide important clinical clues that support the diagnosis of OIS. Numerous changes can be seen in the fundus, including:
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Retinal arterial narrowing.
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Retinal venous dilation without tortuosity.
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Retinal hemorrhages and microaneurysms.
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Neovascularization of the optic disc or retina.
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Cherry-red spot.
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Cotton–wool spots.
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Spontaneous pulsations of the retinal arteries.
Retinal arterial narrowing and straightening, which are associated with areas of focal constriction, are commonly seen in eyes with OIS. Retinal veins may exhibit beading similar to that seen in diabetic retinopathy. Retinal veins are often dilated but not characteristically tortuous or only minimally so ( Fig. 6.23.1 ). This latter feature may help to ophthalmoscopically differentiate OIS from CRVO, in which retinal veins are both dilated and often markedly tortuous.
Retinal hemorrhages are seen in 80% of affected eyes. Typically, these are deep retinal hemorrhages of the dot-and-blot variety, though hemorrhages from ruptured microaneurysms and less frequently nerve fiber layer hemorrhages can also be seen. Characteristically, hemorrhages are found in the midperiphery but can extend into the posterior pole ( Fig. 6.23.2 ). Neovascularization, which ranges from mild to severe, may occur on the optic disc in more than one-third of patients who have OIS. Retinal neovascularization has been described in 8% of eyes.
During examination, a cherry-red spot is seen in 12% of eyes with OIS. This finding most commonly occurs as the IOP from neovascular glaucoma exceeds the central retinal artery’s perfusion pressure. Cotton–wool spots and spontaneous pulsations of the retinal arteries are each found in 5% of eyes that have the syndrome. They are typically multiple and occur predominantly in the peripapillary region. When not present spontaneously, retinal arterial pulsations can be elicited easily by minimal pressure on the globe, because of the severe diminution in ocular perfusion pressure. In contrast, eyes that have nonischemic CRVO require a normal amount of digital pressure to induce retinal arterial pulsations. Though rarely performed currently, ocular plethysmography can be used to quantitatively assess diminished ocular perfusion pressure in OIS. Ischemic optic neuropathy, which presents with acute, pale swelling of the disc, has been infrequently reported in eyes affected by OIS. Otherwise, the optic disc tends to be normal in appearance, unlike the disc edema seen with central retinal vein occlusion.
Symptoms
A history of transient vision loss is reported by 10%–15% of patients with OIS. Decreased visual acuity is present in over 90% of affected patients at initial evaluation. Loss of vision generally occurs gradually, over a period of weeks to months, but can occur abruptly. The severity is variable: 35% of affected eyes at the time of evaluation have a visual acuity of 20/40 (6/12) or better; 30% range from 20/50 (6/15) to 20/400 (6/120); in 35%, acuity is sufficient to count fingers or worse. The absence of light perception is an uncommon finding initially but may develop as a sequela of severe posterior segment ischemia frequently in combination with neovascular glaucoma. Varying patterns of visual field loss, positive visual phenomena, and prolonged recovery of vision after exposure to bright lights are also associated symptoms. A dull ache over the eye or brow, referred to by some authors as ocular angina, is reported in up to 40% of patients with OIS and can result from ischemia of the globe or elevated intraocular pressure (IOP) caused by neovascular glaucoma.
Anterior Segment
Anterior segment findings in OIS are common and rarely may be the sole ocular manifestation of carotid occlusive disease. Anterior segment neovascularization in a nondiabetic patient without evidence of venous occlusive disease or other predisposing cause, is suggestive of OIS. Approximately two-thirds of eyes exhibit neovascularization of the iris at initial examination, with neovascular glaucoma seen in half of these eyes. Despite complete angle closure by fibrovascular proliferation, some patients will demonstrate normal IOP due to decreased aqueous humor production as a result of impaired ciliary body perfusion from carotid occlusion. Anterior uveitis in eyes that have OIS has been well described. Iritis, present in 20% of these eyes, is generally mild. Flare is a more prominent feature than the cellular response, and keratitic precipitates are seen infrequently. The possibility of OIS must be considered in patients over 50 years of age who have new-onset iritis. Lens opacification, even formation of a mature cataract, may occur in the end stages of OIS.
Posterior Segment
Posterior segment signs are more frequent than those in the anterior segment and provide important clinical clues that support the diagnosis of OIS. Numerous changes can be seen in the fundus, including:
- •
Retinal arterial narrowing.
- •
Retinal venous dilation without tortuosity.
- •
Retinal hemorrhages and microaneurysms.
- •
Neovascularization of the optic disc or retina.
- •
Cherry-red spot.
- •
Cotton–wool spots.
- •
Spontaneous pulsations of the retinal arteries.
Retinal arterial narrowing and straightening, which are associated with areas of focal constriction, are commonly seen in eyes with OIS. Retinal veins may exhibit beading similar to that seen in diabetic retinopathy. Retinal veins are often dilated but not characteristically tortuous or only minimally so ( Fig. 6.23.1 ). This latter feature may help to ophthalmoscopically differentiate OIS from CRVO, in which retinal veins are both dilated and often markedly tortuous.
