bilateral visual loss (ie, cortical blindness) or a homonymous hemianopia, often in association with brainstem and cerebellar symptoms or deficits.
A binocular visual disturbance having a geometric quality (eg, a hexagonal “chicken wire” pattern) strongly suggests occipital lobe dysfunction (eg, migraine, ischemia, or seizure). Whiteout of vision in both eyes simultaneously or a gradual constriction (ie, “closing in”) of peripheral vision without positive visual phenomena may also signal occipital lobe ischemia.
Associated symptoms and additional signs. Positive visual phenomena and headache accompanying transient visual loss suggest migraine. Persistent headaches and intracranial noises are typical for increased intracranial pressure. In an elderly patient, transient visual loss associated with headaches, weight loss, fever, malaise, and scalp tenderness strongly suggest giant cell arteritis. The presence of other neurologic symptoms and signs can help localize the vascular territory involved. Loss of consciousness, dizziness, diplopia, dysarthria, or focal weakness accompanying the visual loss suggests global perfusion problems, often involving the brainstem or cortex. Skin or joint changes or Raynaud phenomenon may accompany collagen vascular disease.
Donders RC; Dutch TMB Study Group. Clinical features of transient monocular blindness and the likelihood of atherosclerotic lesions of the internal carotid artery. J Neurol Neurosurg Psychiatry. 2001;71(2):247–249.
Examination
Although the patient may report complete recovery of visual function, a thorough examination is crucial to rule out ocular and orbital causes of transient visual loss, to assess the afferent visual function, and to look for retinovascular clues such as emboli, cotton-wool spots, vascular attenuation, or hemorrhage that might suggest the correct diagnosis. Examination should include testing for bestcorrected visual acuity, visual fields, color vision, and relative afferent pupillary defect, as well as dilated ophthalmoscopy. A positive photostress recovery test may indicate macular ischemia (see Chapter 3).
Transient Monocular Visual Loss
Table 5-1 outlines the most common ocular, orbital, and systemic causes of TMVL.
Table 5-1
Ocular Causes
Nonvascular ocular causes of transient visual loss include tear film abnormalities. Blurred vision caused by irregularity of the tear film usually improves with a blink or application of a tear supplement. Slit-lamp examination may reveal an abnormal-appearing tear film with rapid tear breakup time and punctate keratopathy suggestive of keratitis sicca. Dry eyes can also provoke blepharospasm, which can lead to moments of vision loss (see Chapter 11, Fig 11-10). Opacities, inflammation, or blood in the media of the anterior chamber or the vitreous can also cause episodic visual disturbance. For example, recurrent hyphema occasionally causes TMVL in patients with intraocular lenses who have uveitis-glaucoma-hyphema (UGH) syndrome.
Transient monocular visual obscurations accompanied by halos and pain should always prompt gonioscopy of the anterior chamber angle to assess for angle-closure glaucoma. The anterior lens should be inspected for glaukomflecken, which indicate prior episodes of angle-closure glaucoma.
Transient visual loss, prolonged visual recovery, or persistent afterimages following exposure to bright light (eg, sunlight) suggests macular disorders, such as detachment or age-related macular degeneration, or ocular ischemia. In such patients, results of a photostress recovery test are often abnormal (see Chapter 3). At times, patients with well-developed papilledema or congenital disc anomalies such as drusen or coloboma experience grayouts or blackouts of vision. Such episodes are typically brief and often precipitated by changes in posture, although they may occur spontaneously. Dimming of vision lasts less than 10 seconds, may involve 1 eye at a time, and clears completely. In patients with idiopathic intracranial hypertension, these obscurations are not prognostic of optic nerve damage (see Chapter 4).
Kaiboriboon K, Piriyawat P, Selhorst JB. Light-induced amaurosis fugax. Am J Ophthalmol. 2001;131(5):674–676.
Orbital Causes
Sometimes TMVL is specifically induced by moving the eyes toward a certain direction, particularly downward. Such a history of gaze-evoked visual loss suggests an orbital mass such as hemangioma or meningioma. The mechanism is presumably ischemia from positional vascular obstruction. Other orbital findings such as proptosis or limited ocular motility are usually revealed through careful examination.
Otto CS, Coppit GL, Mazzoli RA, et al. Gaze-evoked amaurosis: a report of five cases. Ophthalmology. 2003;110(2):322–326.
Systemic Causes
After ocular and orbital causes of TMVL have been ruled out, retinovascular and cardiovascular causes must be considered. Amaurosis fugax (“fleeting blindness”) is used to describe TMVL due to retinal emboli. Visual loss is typically abrupt, painless, and descends (or ascends) like a curtain over part or all of the visual field in 1 eye. Visual loss usually resolves in 10–15 minutes but can take up to 1 hour in some cases. At resolution, the curtain may either retract or dissolve like a clearing fog. Amaurosis fugax is not associated with other neurologic deficits. Results of ocular examination of patients with this condition are often normal, although abnormalities of the retinal vasculature are present occasionally.
Emboli
In the late 1950s, C. Miller Fisher called attention to retinal emboli as a significant cause of TMVL after he observed embolic material passing through the retinal circulation. Emboli that cause TMVL usually travel to and lodge in blood vessels that supply the retina. Because emboli can be observed with an ophthalmoscope and frequently appear distinctive, their probable site of origin can often be inferred. Such an inference may be crucial in directing appropriate patient evaluation.
The 3 most common types of emboli—cholesterol (Hollenhorst plaque), platelet-fibrin, and calcium—are shown in Figure 5-1 and their characteristics are reviewed in Table 5-2. Other less common varieties of emboli include those resulting from cardiac tumors (myxoma), fat (long-bone fractures, pancreatitis), sepsis, talc, air, silicone, and depot drugs (corticosteroids).
Figure 5-1 Common retinal emboli. A, Cholesterol embolus (Hollenhorst plaque) at the bifurcation of a retinal arteriole. B, Platelet-fibrin embolus. C, Calcific embolus with branch retinal artery occlusion. (Courtesy of Karl C. Golnik, MD.)
Table 5-2
Atheroma formation occurs most commonly at the bifurcation of the common carotid artery into the internal and external carotid arteries and in the carotid siphon (Fig 5-2). Atheromas can remain stationary, become fibrotic, regress, ulcerate, narrow and occlude the lumen, or release emboli. It is thought that the internal carotid lumen must be reduced by 50%–90% before distal flow is affected. Hypertension, diabetes mellitus, hypercholesterolemia, and smoking are treatable risk factors.
Cardiac emboli can arise from many causes, including
ventricular aneurysms hypokinetic wall segments endocarditis
infectious (associated with subacute bacterial endocarditis)
noninfectious (marantic) valvular heart disease
mitral valve prolapse atrial myxoma
Figure 5-2 Magnetic resonance angiogram showing high-grade stenosis (arrow) of the cervical internal carotid artery at
the bifurcation. (Courtesy of Aki Kawasaki, MD.)
Other cardiac causes of emboli include cardiac arrhythmia, particularly atrial fibrillation and other paroxysmal arrhythmias, and unsuspected patent foramen ovale with right-to-left cardiac shunt.
Clinical and laboratory evaluation An embolic cause of TMVL requires complete vascular and cardiac evaluation because such patients have increased rates of morbidity and mortality from stroke, myocardial infarction, aortic aneurysm, and other related vascular events. Clinical examination should include measurement of blood pressure, cardiac auscultation, and auscultation for carotid bruits (best heard at the angle of the jaw, where the bifurcation is located). A bruit indicates turbulent flow within the vessel, and it may be heard with narrowing of the external or internal carotid artery. However, a bruit will be absent if flow is undisturbed or if carotid occlusion is complete.
Angiography remains the gold standard for quantifying the degree of carotid stenosis. The procedure is invasive, requiring intra-arterial injection of iodinated contrast dye. In centers where angiography is performed regularly, the risk of serious complications (such as stroke or death) is less than 1%.
Because of the time, expense, and morbidity associated with conventional angiography, noninvasive imaging modalities are often used, especially as screening tests. The 3 most frequently used modalities are carotid ultrasonography (duplex scanning), magnetic resonance angiography (MRA), and computed tomographic arteriography (CTA). Ultrasonography is a sensitive method of detecting ulcerated plaques, but its reliability varies. Results of MRA and CTA studies tend to overestimate the degree of carotid stenosis, especially stenosis of moderate to high grade, compared with conventional angiography. But besides being noninvasive, MRA and CTA allow the visualization and characterization of the plaque in question, as well as of the surrounding arterial wall. MRA, along with magnetic resonance imaging (MRI), is extremely useful for detecting carotid artery dissection.
Echocardiography is useful for detecting valvular and cardiac wall defects, intracardiac tumors, and large thrombi. Transesophageal echocardiography is more sensitive than conventional transthoracic echocardiography. A normal-appearing echocardiogram does not exclude the possibility of emboli because very small particles are not revealed. With carotid artery disease, a routine echocardiogram is mandatory. Coincident myocardial and cerebral ischemia should always be considered. Prolonged inpatient cardiac monitoring or ambulatory Holter monitoring may document previously undetected cardiac arrhythmias. Suspected endocarditis should prompt blood culture testing.
If a cardiac or carotid source of embolism formation is not found, other systemic processes may be contributing to stroke. Major risk factors include advanced age, hypertension, hypotension and syncope (possibly iatrogenic from overtreatment of hypertension or from other medications), ischemic heart disease, diabetes mellitus, hypercholesterolemia, smoking, and sleep apnea. Most of these conditions are treatable. Laboratory studies should be obtained to evaluate for these conditions and any others under clinical suspicion such as thyroid disease, hypercoagulable states, collagen vascular diseases, vasculitis, or syphilis.
Biousse V, Trobe JD. Transient monocular visual loss. Am J Ophthalmol. 2005;140(4):717–721. Epub 2005 Sep 2.
Newman NJ. Evaluating the patient with transient monocular visual loss. The young versus the elderly. Ophthalmol Clin North Am. 1996;9:455–465.
Prognosis and treatment Among patients with TMVL, significant carotid artery stenosis or occlusion is present in 53%–83%. The risk of stroke after a retinal transient ischemic attack (TIA) related to carotid atherosclerosis is relatively low (2% risk per year) and substantially lower than that after a hemispheric TIA (approximately 8% risk per year). Consequently, the guidelines for management of high-grade (>70%) internal carotid artery stenosis differ slightly between these 2 groups of patients with symptomatic carotid disease, tending to favor medical therapy for patients with isolated TMVL.
However, other factors have been used to stratify stroke risk in patients with TMVL: male sex, age 75 years or older, previous history of hemispheric TIA or stroke, intermittent claudication, stenosis of 80%–94%, and absence of collateral vessels on angiography. Having a greater number of these risk factors was associated with a higher risk of stroke. Patients with none or only 1 of these risk factors had a very low 3-year risk of ipsilateral stroke (1.8%). The stroke risk was 12.3% for patients with 2 risk factors, and for patients with 3 or more risk factors, the stroke risk increased to 24.2%. Thus, surgical management (eg, carotid endarterectomy [CEA]) may have benefit for patients with TMVL who have 3 or more risk factors of stroke.
Based on independent cases or series, CEA is sometimes performed for ophthalmic conditions other than TMVL, such as ocular ischemic syndrome or retinal artery occlusion. However, there are no definitive data on the efficacy of CEA in these conditions.
Carotid artery stenting (CAS) may be a valid alternative to, and a less invasive procedure than, CEA. The Carotid Revascularization Endarterectomy Versus Stent Trial (CREST), a multicenter, randomized prospective clinical trial, found no statistically significant differences between CEA and CAS on stroke rate for up to 4 years postoperatively in symptomatic patients and asymptomatic patients with high-grade (>70%) stenosis. Younger patients (under age 70 years) tended to have slightly better outcomes with CAS and older patients with CEA.
Medical treatment of TMVL due to carotid artery stenosis (ie, retinal TIA) begins with aspirin. Although the addition of dipyridamole is controversial, an aspirin-dipyridamole combination is often prescribed. Clopidogrel bisulfate is useful for patients who are intolerant of or allergic to aspirin. A selective cyclic adenosine monophosphate phosphodiesterase inhibitor, cilostazol, inhibits platelet aggregation and is a direct arterial vasodilator; it may be more protective than either aspirin alone or clopidogrel. Once antiplatelet therapy is maximized, consideration should be given to adding a statin or increasing the dose of a statin that the patient is already taking. There is some evidence that high doses of statins can reduce plaques and the frequency of stroke. Finally, inhibitors of angiotensinconverting enzymes (ACE) and ACE receptor blockers may be useful for their favorable effects on endothelial tissue.
Benavente O, Eliasziw M, Streifler JY, Fox AJ, Barnett HJ, Meldrum H; North American Symptomatic Carotid Endarterectomy Trial Collaborators. Prognosis after transient monocular blindness associated with carotid-artery stenosis. N Engl J Med. 2001;345(15):1084–1090.
Mantese VA, Timaran CH, Chiu D, Begg RJ, Brott TG; CREST Investigators. The Carotid Revascularization Endarterectomy versus Stenting Trial (CREST): stenting versus carotid endarterectomy for carotid disease. Stroke. 2010;41(10 Suppl):S31–34.
Trobe JD. Carotid endarterectomy: who needs it? Ophthalmology. 1987;94(6):725–730.
Additional systemic causes
Other possible systemic causes of transient monocular blindness and carotid territory ischemia are ophthalmic artery disease, giant cell arteritis, Raynaud disease, vasculitis, hyperviscosity syndromes, antiphospholipid antibody syndrome, and vasospasm (migraine). Carotid dissection should be considered in patients with painful ipsilateral monocular visual loss, particularly if associated with Horner syndrome and contralateral neurologic signs (Fig 10-4).
Fisher CM. Observation of the fundus oculi and transient monocular blindness. Neurology. 1959;9(5):333–347.
Ramakrishna G, Malouf JF, Younge BR, Connolly HM, Miller FA. Calcific retinal embolism as an indicator of severe unrecognized cardiovascular disease. Heart. 2005;91(9):1154–1157.
Vasculitis
TMVL in older patients (usually age 50 years or more) can be caused by giant cell arteritis (GCA), and in this setting, TMVL signals impending acute and permanent visual loss in 1 or both eyes. Therefore, in older patients with monocular or binocular transient visual loss, a directed history should inquire about the following symptoms
headache
scalp tenderness jaw claudication weight loss depressed appetite proximal joint pain
muscle aches and myalgias malaise
Tests for erythrocyte sedimentation rate, C-reactive protein concentration, and platelet count should be taken (see also BCSC Section 1, Update on General Medicine). Evidence of choroidal hypoperfusion (low intraocular pressure or changes on fluorescein angiogram) is a suggestive finding. If GCA is the suspected cause of transient visual loss, immediate treatment with high-dose corticosteroids is the only way to prevent progression to permanent visual loss.
Hypoperfusion
Hypoperfusion may lead to TMVL in several situations. The first is in patients with central retinal vein occlusion. Patients may report transient visual impairment lasting seconds to minutes, with recovery to normal vision. Such symptoms may predate more lasting visual loss by days or weeks, or the symptoms may cease when collateral vessels develop.
The second situation is TMVL precipitated by a change in posture from a sitting to a standing position, usually related to cardiac arrhythmia, severe stenosis of the great vessels, or GCA. Here the patient notes progressive restriction of vision from the periphery (“iris diaphragm pattern”), lasting from seconds to 1–2 minutes.
The third entity in which hypoperfusion leads to TMVL is the ocular ischemic syndrome. This syndrome is characterized in part by a hypotensive, ischemic retinopathy with low retinal artery pressure, poor perfusion, and midperipheral retinopathy. Recurrent orbital or facial pain that improves when the patient lies down is highly suggestive of carotid occlusive disease. In the early stages, there may be transient or persistent blurred vision or transient visual loss on exposure to bright light. Dot-and-blot hemorrhages characterize early ocular ischemia. At times, such