Table 24.2 Systemic abnormalities associated with the ocular ischemic syndrome at baseline [43]

on the optic disk, retinal arterial pulsations are always abnormal.

Systemic Associations

The OIS is associated with systemic abnormalities related in some way to atherogenesis (Table 24.2) [43]. The prevalence of systemic arterial hypertension in OIS patients is 73%. Diabetes mellitus is found in 56% of patients, while 50% have had a myocardial infarction, the latter demonstrating that arterial atherosclerosis in an OIS population is not confined to only the eye. Approximately 27% of OIS patients have had a previous stroke, while the stroke rate for people with the OIS is approximately 4% per year [43]. At the time of presentation, almost one-fifth of patients relate a history of having peripheral vascular disease for which previous bypass surgery was required [43].

Mortality data [43] have shown that the 5-year death rate for patients with the OIS is 40% (Fig. 24.15). The leading cause of death is cardiovascular disease, which accounts for about twothirds of cases. Stroke is the second leading cause of death.

Differential Diagnosis

The differential diagnosis for the OIS includes primarily mild (nonischemic) central retinal vein obstruction, diabetic retinopathy, radiation retinopathy, hypertensive retinopathy, and vasculopathies such as those encountered with polycythemia and collagen vascular diseases.

Treatment

Systemic Therapy: Carotid Artery

The natural course of vision loss with the ocular ischemic syndrome is uncertain. Nonetheless, most eyes with the fully developed entity probably have a poor long-term outcome. When iris neovascularization is present, over 90% of eyes become legally blind within a year of discovery [25].

When a carotid artery is 100% obstructed, endarterectomy is generally not effective since a thrombus can propagate anterograde and/or retrograde. In these cases, extracranial to intracranial bypass surgery, usually from the superficial temporal artery to the middle cerebral artery, has been attempted to alleviate the obstruction. Although this procedure was of benefit in 20% (3/15) of cases in salvaging vision in eyes with the OIS, the visual prognosis at 1 year after the surgery was universally poor [25]. Additionally, the procedure has not been shown in a large randomized study to be of benefit in preventing the risk of ischemic stroke [44].

Although there are no randomized studies that compare the natural history of the disease to the course after carotid endarterectomy, this surgery may also stabilize or improve vision in the eyes of patients who undergo successful endarterectomy prior to the development of iris neovascularization [25, 45]. Notwithstanding, the visual results associated with this treatment are fair at best. In the series of Sivalingam et al. [25] at the end of 1 year, 7% of eyes with the ocular ischemic syndrome that underwent endarterectomy experienced visual improvement or stabilization, 33% were unchanged, and 60% had worse vision. Among the 60 total OIS eyes in the group, an endarterectomy was performed for only 3 without iris neovascularization. At the end of 1-year follow-up the vision was better in one, stable in one, and worse in the third.

Endarterectomy appears to rarely cause regression of iris neovascularization eyes with the OIS [46]. It should be noted that eyes with the OIS will occasionally develop a severe increase in intraocular pressure after ipsilateral carotid

endarterectomy. This is most likely to occur in eyes with iris neovascularization and anterior chamber angle compromise from fibrovascular tissue formation. Although aqueous outflow is impaired in such eyes, ciliary body perfusion and aqueous humor formation are also decreased secondary to the carotid stenosis. When the carotid obstruction is suddenly reversed, ciliary body perfusion and aqueous humor formation increase, but the outflow obstruction in the anterior chamber angle is still present. Thus, the intraocular pressure rises drastically. Ciliary body destructive procedures or glaucoma filtering surgery may be required in these cases [47, 48].

Several large randomized studies have recently been published concerning the indications for carotid endarterectomy in general [49–52]. Carotid endarterectomy has been proven to be efficacious both in symptomatic patients with high-grade (70–99%) carotid artery stenosis and in asymptomatic patients with greater than (or equal to) 60% stenosis. Specifically, the investigators of the North American Symptomatic Carotid Endarterectomy Trial [50] noted a 17% absolute risk reduction in the cumulative 2-year risk of ipsilateral stroke and a 10% absolute risk reduction in fatal ipsilateral stroke when those randomized to endarterectomy were compared to those who were treated medically. The European Carotid Surgery Trialists’ Collaborative Group [49] also was able to demonstrate a similar treatment effect of carotid endarterectomy for patients

with 70–99% stenosis (sixfold reduction in 3-year risk of ipsilateral stroke) but also found that in the 0–29% stenosis group the early risks of surgery (2.3% died or had a disabling stroke within 30 days of surgery) outweighed the 3-year benefit when compared to medical therapy.

The investigators of the Asymptomatic Carotid Atherosclerosis Study [51] were able to demonstrate an aggregate risk reduction of 53% in the incidence of death or stroke, when those randomized to surgery were compared to those who received medical treatment. Asymptomatic patients with carotid artery stenosis of 60% or greater reduction in diameter were eligible to benefit. Accordingly, any patient with the OIS and severe carotid artery stenosis should be considered for carotid endarterectomy.

Marx et al. [53] demonstrated that percutaneous carotid artery angioplasty with stenting stabilized or improved vision in each of three cases, while Kawaguchi et al. [54] demonstrated that stenting of the carotid artery improved the OIS in seven of eight patients. Stenting for restenosis of the carotid artery and the OIS has also been reported [55].

Ophthalmic Therapy

Full scatter panretinal laser photocoagulation has been advocated for OIS eyes with iris neovascularization and/or posterior segment neovascularization