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Patient with type 2 diabetes presents with mild unilateral retinopathy
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A 73-year-old African American man presented for a periodic eye exam. He expressed no visual complaints and denied any changes in his visual acuity since his last exam 5 years ago. His medical history consisted of type 2 diabetes for 15 years and hypertension. Medications included metformin, glipizide, and lisinopril. Recent HbA1c was 6.8%, and his blood pressure was 148/80 mm Hg.
A fundus photo of the patient’s right eye shows no signs of diabetic retinopathy. The fundus photo of the left eye was of poor quality secondary to dense asteroid hyalosis. Images here show examples of midperipheral retinal hemorrhages and cotton-wool spots along inferior temporal arcade.
Images: Perkins E
At examination, his best-corrected visual acuity was 20/20 OD and 20/25 OS. His anterior segments were unremarkable. The corneas were clear, conjunctivas were white, anterior chambers were deep and quiet, and irides were intact and negative for neovascularization. Intraocular pressures were 20 mm Hg OD and 21 mmHg OS.
Dilated exam revealed 2+ nuclear sclerosis cataracts in both eyes and dense asteroid hyalosis in the left eye. The optic nerves had good color, small cup-to-disc ratios and intact neural retinal rims. The retinal venules were dilated without tortuosity, with the left eye more pronounced than the right.
The right fundus showed no signs of diabetic retinopathy or hypertensive retinopathy. The left fundus demonstrated a few midperiphery blot hemorrhages and a single cotton-wool spot along the inferior temporal arcade.
The differential diagnosis for unilateral retinopathy includes diabetic retinopathy, central retinal vein occlusion, chronic ocular ischemia and ocular ischemic syndrome. Diabetic retinopathy is typically characterized by the presence of microaneurysms, dot-blot hemorrhages, cotton-wool spots, hard exudates and venule caliber changes. Diabetic retinopathy tends to be bilateral and symmetric. Unilateral or marked asymmetric retinopathy in a patient with diabetes warrants further investigation.
An audible bruit was auscultated at the angle of the jaw on the left side. The patient denied experiencing any visual disturbances or neurological symptoms such as numbness or weakness. A tentative diagnosis of early chronic ocular ischemia was given based on the presence of a bruit and unilateral retinopathy limited to the posterior segment. A carotid artery duplex Doppler study was ordered and performed within 2 weeks of the eye exam.
The results of the carotid artery ultrasound found a mild stenosis (less than 49%) of the right internal carotid artery and a severe stenosis (70% to 99%) of the left internal carotid artery. Primary care was notified and consults were placed to cardiology and vascular surgery. Vascular surgery ordered a computed tomography angiography (CTA) to confirm the ultrasound findings. The CTA estimated the stenosis of the left carotid artery to be moderate (50% to 69%) instead of severe.
Elizabeth Perkins
Carotid artery stenosis is a progressive narrowing of the arteries caused by atherosclerotic changes in the blood vessel walls. Diabetes is one of the leading vascular risk factors for the development of atherosclerosis. One in five patients with diabetes and unilateral or pronounced asymmetric retinopathy will have a significant carotid artery stenosis (Duker and colleagues).
Effects on ocular blood flow
Carotid artery occlusive disease can have a significant effect on ocular blood flow. Kawaguchi and colleagues studied ocular circulation before and after carotid artery revascularization surgery in 90 patients with moderate to severe carotid artery stenosis and signs of ocular ischemia. Using color Doppler flow imaging they recorded a marked decrease in peak systolic flow velocities within the ophthalmic artery (OA) and the central retinal artery (CRA) compared to those of the controls. A few of the participants with high-grade carotid artery stenosis demonstrated reversed blood flow within the OA. Instead of anterograde or towards the globe, the blood flowed away from the globe towards the ICA. Following revascularization surgery the peak systolic flow velocities in both the OA and CRA returned to normal levels, and any reverse flow within OA were corrected to anterograde.
Reduced ocular blood flow can lead to chronic ocular ischemia. Initially chronic ocular ischemia can have subtle ocular manifestations involving the posterior segment only. This is considered by some to be hypoperfusion retinopathy and an early stage of chronic ocular ischemia. It is evident by unilateral dilated retinal venules, midperipheral hemorrhages, cotton-wool spots and microaneurysms. Up to 20% of patients with carotid artery stenosis will manifest hypoperfusion retinopathy (Malhotra and Gregory-Evans). This may be the initial indicator of carotid artery occlusive disease.
When chronic ocular ischemia progresses to involve both the anterior and posterior segments it is considered to be ocular ischemic syndrome (OIS). OIS is a rare and devastating form of chronic ocular ischemia. The annual incidence of OIS is estimated to be 7.5 cases per million, and it has a 5-year mortality rate of 40% (Malhotra and colleagues). Typically it requires a carotid artery stenosis of 90% or greater to evolve (Tahmasebpour and colleagues). At that degree of stenosis, the perfusion pressure within the CRA is diminished by 50%. Patients with a total occlusion of the internal carotid artery may not develop OIS if anterograde flow is maintained within the ophthalmic artery by a well-developed collateral circulation via the circle of Willis.
The classic triad of OIS is dilated retinal veins, midperipheral retinal hemorrhages and rubeosis iridis. Neovascular glaucoma holds a poor visual prognosis, with 95% of patients developing profound vision loss within a year (Atebara and Brown).
Treatment
Treatment of carotid artery stenosis depends on the degree of the stenosis and whether the patient is symptomatic or asymptomatic. Two large randomized studies, the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and the European Carotid Surgery Trial (ECST), demonstrated that carotid endarterectomy (CEA) surgery was superior over aspirin in preventing a stroke in symptomatic patients with carotid artery stenosis greater than 50% (Biller and Thies).
Arrow points to the narrowing of the left internal carotid artery on the patient’s axial CT scan.
CEA to treat asymptomatic carotid artery stenosis is controversial because the stroke risk for patients not experiencing any neurological symptoms is 2% or less, while the perioperative risk of stroke and death is between 2% to 4% (Eliaswiz and colleagues). According to the American Heart Association, it is appropriate to consider CEA in asymptomatic patients with artery stenosis of greater than 60% if the life expectancy is at least 5 years and the surgical risk is less than 3% (Biller and colleagues).
For patients who are not candidates for surgical intervention, following a comprehensive medical therapy program that combines both medication and lifestyle modifications can greatly decrease their risk of stroke. Important lifestyle modifications include regular exercise, smoking cessation, proper diet and blood pressure management. Recommended medications include antiplatelets, anticoagulants, statin drugs that are known to stabilize atherosclerotic plaques and antihypertensives. Angiotensin-converting enzyme inhibitors are especially effective in reducing inflammation and preventing thrombosis formation. Adherence to a combined medical therapy regimen can reduce the relative risk of a stroke by up to 80% (Louridas and Junaid). Stroke is the third leading cause of death and the leading cause of serious long-term disability in the U.S.
This patient’s treatment
Management of this patient involves close follow-up by primary care, cardiology and optometry. The patient was initially seen every 2 to 3 months but is now being monitored every 6 months for the onset of neurological symptoms, a worsening of ocular ischemia or an increase in the degree of stenosis to the level appropriate for surgical intervention. Changes to the patient’s medications include the addition of aspirin, simvastatin and amlodipine to lower the blood pressure.
The Northern Manhattan Study (NOMAS) found that 25% of asymptomatic participants with an audible bruit had a hemodynamically significant carotid artery stenosis of 60% or greater (Ratchford and colleagues). Early diagnosis of carotid artery occlusive disease with the initiation of a comprehensive medical therapy regimen and surgical intervention when indicated provides the best approach to preventing a stroke and preserving vision.
This case illustrates the important role optometrists play in the diagnosis of carotid artery occlusive disease. Unilateral or pronounced asymmetric retinopathy in a patient with diabetes deserves a second look and may be the first indicator of carotid artery stenosis. Auscultation for a carotid bruit is a quick and valuable screener for asymptomatic patients and, if present, justifies further evaluation.