Asymmetric diabetic retinopathy

Abstract

Diabetic retinopathy is primarily a microangiopathy. In response to the ischemia, retinal tissues release various angiogenic and inflammatory factors that enhance vascular growth and permeability, leading to progression of diabetic retinopathy. The fundoscopic findings in the vast majority of patients tend to be symmetrical. Asymmetric findings should prompt further investigation. A 73-year-old man with Type 2 diabetes mellitus for the past 15 years was routinely followed-up on an annual basis in the eye clinic. Over the duration of follow-up, fundoscopy had shown only minimal background diabetic retinopathy. Over a period of 10 months, the patient developed very marked asymmetric retinopathy that was resistant to extensive treatment with panretinal photocoagulation. During this period, the patients HbA1c was 8.6%. His medical history included hypertension and hypercholesterolemia, for which he was on oral medication. He also had a history of peripheral vascular and ischemic heart disease. At examination, corrected visual acuities were 6/12 in the right eye and 6/6 in the left eye. The right fundus had extensive proliferative changes, with a fan of new vessels arising from the optic disc with an inner fibrous band. In contrast, the left fundus showed signs of mild non-proliferative diabetic retinopathy (Fig. 1). Ocular examination was otherwise normal. In view of the asymmetry in the severity of the patient’s diabetic retinopathy and his history of vascular disease, underlying ocular ischemic syndrome (OIS) was suspected. Clinical fundus photographs showing the (a) left and (b) right fundi of a 73-year-old diabetic man with severe right carotid artery stenosis. Further examination revealed a considerably reduced right carotid artery pulse. This was subsequently confirmed by Doppler studies that showed near complete occlusion of the right internal carotid artery and 50% stenosis of the left internal carotid. Carotid stenosis was undoubtedly the predominant factor in producing such marked asymmetric retinopathy. The resultant ocular ischemia caused by aortic arch atherosclerosis or by stenosis of the carotid arteries may cause neovascularization of the iris, disc, and peripheral retina. Although panretinal photocoagulation may be of some benefit in such patients, the outcome is usually less successful, perhaps because the vasoproliferative stimulus is so intense and diffuse within the eye. A variable spectrum of signs and symptoms may result from chronic ocular hypoperfusion. Collectively, they may be encompassed under the heading of OIS. This was first described by Kearns and Hollenhorst in 1963.1 The mean age at presentation is usually 65 years and the condition affects men twice as frequently as it does women. In 20% of cases, the syndrome affects both eyes. Symptoms of OIS include decreased vision, eye pain (including a dull ache over the eyebrow) and a history of transient ischemic attacks or amaurosis fugax. A constellation of signs may be seen in the fundus, including retinal arterial narrowing, retinal venous dilatation without tortuosity, retinal hemorrhages and microaneurysms, pulsation of the retinal arteries, cotton wool spots, and retinal neovascularization. Differentiation from proliferative diabetic retinopathy may, indeed, be difficult. Usually, OIS is associated with widespread atherosclerosis: 50% of patients have evidence of previous ischemic heart disease, whereas previous cerebrovascular accidents have occurred in 25% of patients.2 The severity of the syndrome is reflected by a 40% 5-year mortality rate, the main cause of death being ischemic heart disease.2 The presentation of marked asymmetric retinopathy should raise suspicion of OIS and should prompt urgent investigation of blood supply to the head and neck, namely the patency of the carotid arteries. Indeed, reversal of the carotid stenosis may be the most important avenue to maintain or improve vision in such cases. The North American Symptomatic Carotid Endarterectomy Trial3 found that the 2-year stroke rate was 9% in patients who had undergone carotid endarterectomy compared with 26% in patients only managed with antiplatelet therapy. However, the decision to undertake carotid endarterectomy may be difficult given the high rate of immediate postoperative risk of severe stroke (2.1%) compared with only 0.9% in patients treated with antiplatelet therapy.3 In summary, marked asymmetrical diabetic retinopathy should raise suspicion of OIS and prompt further investigation. This is important because OIS is associated with high morbidity and mortality from both ischemic heart disease and cerebrovascular accident. Early intervention, including carotid endarterectomy, may result in improved outcome for these patients.