Ocular Ischemic Syndrome With Congenital Absence of Internal Carotid Artery

Abstract

Purpose:

This article describes a case of ocular ischemic syndrome (OIS) in a patient with a congenitally absent left internal carotid artery (ICA).

Methods:

Retrospective case report with anterior-segment and fundus photography, fluorescein angiography (FA), and computerized tomography angiography (CT-A).

Results:

A 31-year-old-man was found to have neovascularization of the iris (NVI) and angle of the left eye. FA showed capillary nonperfusion in the temporal periphery. He required intravitreal bevacizumab and triamcinolone injections and 2 panretinal photocoagulation treatments for persistent rubeosis and cystoid macular edema. Transient right-eye vision loss prompted CT-A, revealing an absent left ICA. Three years following presentation, FA continued to show delayed arteriovenous flow suggestive of OIS. He has required intravitreal bevacizumab injections every 12 weeks for persistent NVI.

Conclusion:

Congenitally absent left ICA with resultant cerebrovascular insufficiency is a rare cause of OIS, underscoring the pathophysiological principles of insufficient blood supply to the ophthalmic artery.

Introduction

Ocular ischemic syndrome (OIS) is a rare ophthalmic condition caused by chronic hypoperfusion of the common or internal carotid artery (ICA), resulting in insufficient blood supply to the ophthalmic artery. Presentations of the condition include vision loss, orbital pain, iris neovascularization, corneal edema, neovascular glaucoma, dilated retinal veins, microaneurysms, retinal hemorrhage, and more. ¹ While atherosclerosis is the main cause of OIS, other systemic vascular diseases such as peripheral vascular disease, hypertension, diabetes, and more have been associated. ² Less-common causes of reduced blood flow to the eye include giant-cell arteritis, aortic arch syndrome, and Takayasu arteritis. ²

The absence of an ICA is a rare vascular anomaly occurring in less than 0.01% of the population. ^3,4 The most common pathway of collateral circulation is through the circle of Willis. ⁵ This rare vascular anomaly can be incidentally found on imaging with sufficient collateral circulation pathways or present as acute ischemia such as transient ischemic attack, stroke, amaurosis fugax, or ischemic optic neuropathy. ⁶ There has not previously been any reported case of absent ICA with OIS, to the best of the authors’ knowledge.

Case Report

A 31-year-old white man with a medical history of bilateral congenital glaucoma, hypertension, and treated retinal tear was found to have new neovascularization of the iris (NVI) and angle. Visual acuity was 20/40 in the right eye and 20/50 (pinhole 20/40) in the left eye. Intraocular pressure (IOP) was 18 mmHg in the right eye and 6 mmHg in the left eye. Anterior-segment examination of the right eye showed buphthalmos and mild corneal endothelial striae, but an otherwise normal anterior chamber without rubeosis. There was a centered posterior-chamber intraocular lens (PCIOL) intact with peripheral iridotomy superiorly.

Posterior-segment examination of the right eye showed optic nerve cupping with a cup-to-disc ratio of 0.9. The vitreous and retina examination was unremarkable. Upon examination of the left eye, mild buphthalmos was observed. The anterior segment showed significant corneal microcystic edema with endothelial striae. The anterior chamber was of normal depth and quiet. The iris examination showed new NVI and angle at 3, 6, and 9 o’clock in addition to a peripheral iridotomy superiorly. The PCIOL was centered and intact. Corneal clouding due to endothelial compromise limited the view to the fundus. Limited posterior-segment examination of the left eye showed optic nerve cupping and a well-treated retinal tear at 10 o’clock. Congenital glaucoma caused Haab striae and thus blurry images on fluorescein angiography (FA) of the left eye. The first image was captured at 27 seconds. Arteriovenous filling was complete and choroidal filling was unable to be appreciated. Mid- to late-phase FA showed capillary nonperfusion and retinal vascular changes in the periphery with a wedge-like infarct temporally, suggestive of peripheral retinal ischemia. FA of the right eye had no abnormal findings. Fundus photography of the left eye and FA of the left eye at time of presentation are shown in Figure 1. The patient was treated empirically with an intravitreal injection of bevacizumab in the left eye.

Figure 1.

(A) Fundus photograph of the left eye at presentation showing optic nerve cupping and vitreous debris. (B) Fluorescein angiography (FA) of the left eye at presentation, blurry due to corneal edema, showing first image captured at 27 seconds. (C) Mid-phase FA at 43 seconds with capillary nonperfusion in the periphery. (D) Late-phase FA at 2 minutes and 26 seconds with marked temporal capillary nonperfusion, no evidence of neovascularization, and scattered microvascular abnormalities.

Over the next 11 months, the patient’s vision vacillated between 20/30 and 20/400 in the left eye, depending on the amount of corneal edema and cystoid macular edema (CME). At times, he complained of photophobia and a “gray spot” over his central vision in the left eye. FA at follow-up appointments showed delayed choroidal flush at 16 seconds. Over that period, the patient received an additional 7 intravitreal bevacizumab injections, 2 intravitreal triamcinolone injections, and 2 panretinal photocoagulation (PRP) treatments for rubeosis and CME.

Eleven months following presentation, the patient endorsed worsening of the gray spot in his left eye but also experienced a sudden 30-minute episode of temporal vision loss in his right eye, prompting a hypercoagulability workup for suspected embolus, which returned negative for any inherited thrombophilia (including normal complete blood count with differential, prothrombin time, partial thromboplastin time, dilute Russell viper venom time, antithrombin III activity, beta 2 glycoprotein 1 antibodies, anticardiolipin antibodies, protein S antigens, protein C and S activity, factor VIII activity, activated protein C resistance ratio, paroxysmal nocturnal hemoglobinuria evaluation, and negative factor V Leiden mutation, prothrombin-20210A mutation, phospholipid neutralization, lupus anticoagulant assay, and antinuclear antibody screen). Angiography of the right eye showed retinal arteriole transit time of 19 seconds with focal hyperfluorescence consistent with microaneurysms. The patient was referred to a cardiologist for a cardiovascular workup. A 24-hour Holter monitor revealed sinus rhythm without significant arrhythmias. A carotid duplex scan found mild intimal thickening of the right ICA and suggested left internal and common carotid artery occlusion without Doppler flow. A follow-up computerized tomography angiograph (CT-A) of the neck was completed, revealing an aberrant right subclavian artery (arteria lusoria) and absent left common carotid and ICA (Figure 2). What was initially thought to be occlusion on the ultrasound scan was found to be hypoplastic tissue on CT-A. Given his abnormal cardiovasculature, the diagnosis of OIS of both eyes, left worse than right, was made.

Figure 2.

(A) Normal right common carotid artery indicated by arrows pointing right. Common carotid artery bifurcates into the internal carotid artery (arrowhead) and external carotid artery (arrow pointing left). (B) No evidence of left common carotid or left internal carotid artery. Left external carotid artery originated from the aortic arch indicated by arrows pointing left.

Over the next 3 years and 7 months, the patient received 11 intravitreal bevacizumab injections in the left eye and 3 intravitreal triamcinolone injections in the left eye. He underwent bilateral Ahmed valve shunt placement for better IOP control for congenital glaucoma. Descemet stripping automated endothelial keratoplasty (DSAEK) surgery was performed on the left eye to restore corneal endothelial function, resulting in resolution of the corneal clouding and improvement of the view to the fundus, which showed PRP scars and recurrent CME. He continued to experience blurry vision in both eyes, with decreased vision more notable in the morning. The former complete dark circle in the center vision of his left eye improved to appear as a “dark ring.” FA retinal artery transit time 3 years after initial presentation still showed a delay of 37 seconds on the left eye (Figure 3). Iris rubeosis continues to persist on the left eye, requiring continued intravitreal bevacizumab injections every 12 weeks to limit angle rubeosis (Figure 4). No retinal treatments have been given to the right eye. Verbal informed consent for use of patient information and images was obtained from the patient.

Figure 3.

Fluorescein angiography (FA) of the left eye 3 years following initial presentation showing (A) delayed arteriovenous transit time of 37 seconds, (B) venous laminar phase at 42 seconds, (C) full arteriovenous phase at 58 seconds, and (D) late-phase FA at 4 minutes and 28 seconds.

Figure 4.

Neovascularization of the iris at 4 years and 6 months after initial presentation of rubeosis.

Discussion

Patients with absent ICA often present with symptoms of cerebrovascular insufficiency such as transient ischemic attacks, with collateral circulation commonly through the circle of Willis. ⁴ Alternative presentations of unilateral ICA include mass effect symptoms, aneurysm complications, and a case of congenital Horner syndrome in which the patient presented with unexplained visual blurring and transient vision loss as well. ^4,7 This patient did not have signs or symptoms of Horner syndrome. Postulated causes of congenital unilateral ICA absence focus on mechanical and hemodynamic stresses placed on the embryo during development, including constriction by amniotic bands. ^4,8

Many cases of absent ICA remain asymptomatic until later in life when atherosclerosis begins to compromise the sole carotid artery responsible for cerebrovascular adequacy. ⁴ The carotid duplex scan revealed intimal thickening in the patient’s right ICA, which suggests that this typically minor disease burden in patients with normal vascularization was overwhelming the ability of a stressed vascular network to compensate adequate blood flow to the left ophthalmic circulation.

Much of the progression and severity of OIS depends on patients’ collateral circulations, such as between both ICAs. Therefore, those with collateral reserve may not develop OIS even if one ICA is completed occluded. ² Conversely, poor collateral circulation leads to a reduced threshold for disease. ² This patient’s CT-A showed a very enlarged left posterior communicating artery, which may be related to his collateral circulation and anastomoses in place. This compensatory pathway may have proved insufficient due to the developing atherosclerotic burden of the right ICA, resulting in chronic hypoperfusion of the ophthalmic artery. This may explain the patient’s abnormally young age to suffer from OIS, which rarely occurs before age 50 and has a mean age of 65 years at presentation. ²

Both Mendrinos et al and Hoyt report that transient monocular vision loss is regarded as a hallmark of carotid insufficiency, and Zink et al report that it is also a common presenting symptom of unilateral absent ICA. ^2,6,9 Our patient’s transient visual loss in his right eye prompted the imaging that led to the vascular anomaly findings. Given that this symptom occurred in the eye ipsilateral to the present ICA, carotid insufficiency may have affected both eyes through decreased total blood flow. The patient’s morning visual difficulties may suggest postural change decreasing perfusion pressure, and his light sensitivity may be related to bright light increasing retinal metabolic demands. ^2,10,11 Both scenarios have been documented as examples of borderline ocular blood flow unable to sustain maintenance in stress-inducing conditions. ²

The CT-A also showed an aberrant right subclavian artery, also known as arteria lusoria. Anatomically, in place of a brachiocephalic trunk arising from the aorta, 4 arteries arise in this order: right common carotid, left common carotid, left subclavian, right subclavian. ¹² The aberrant right subclavian then crosses the midline, typically behind the esophagus. ¹² The prevalence is 1.23%, with symptoms occurring in 7% to 10% of adult patients. ^12,13 Commonly reported symptoms include dysphagia, dyspnea, retrosternal pain, cough, and weight loss. ¹² There is no known association with OIS to the best of the authors’ knowledge.

This patient’s absent left ICA and resultant suspected cerebrovascular insufficiency causing OIS is a rare presentation of an uncommon condition, but it underscores the principles of the disease pathophysiology. To the authors’ knowledge, this is the first case of its kind to be reported.