Cervical Carotid Atherosclerosis: Retinal Embolism (Hollenhorst Plaque)
Atheromatous plaques in the cervical carotid bifurcation may send platelet-fibrin-cholesterol emboli up into the retinal arterioles. As they briefly interrupt retinal blood flow, these "Hollenhorst plaques" often cause transient monocular loss of vision lasting from seconds to minutes. They frequently get trapped at vessel bifurcations but do not obstruct flow there. Eventually they break up and disappear.
In middle-aged and elderly adults, abrupt transient monocular visual loss is presumptively caused by carotid-source emboli, although there are other reasons for this. In young individuals, transient vasospasm, perhaps a type of migraine, is the most common presumed cause, as carotid atheroma is rarely found.
What to do?
In adults aged over 40, a history of abrupt monocular visual loss should prompt an ophthalmologic examination to search for Hollenhorst plaques or other causes of this symptom.
Even if the ophthalmologic exam is normal, ultrasonography of the carotid arteries is recommended to rule out a source of embolism, particularly in patients with atheromatous risk factors. Based on collaborative trials, carotid endarterectomy is justified if high-grade (>70%) stenosis is found.
What should you do if you happen to find a Hollenhorst plaque in a patient without a history of visual loss? This is controversial. Most observers believe that it should prompt carotid ultrasound studies to establish whether there is substantial atherosclerosis. However, carotid endarterectomy is not indicated even in the presence of high-grade stenosis because the benefit of surgery is too low to justify its risks.