This article includes discussion of ulnar neuropathies, Guyon canal neuropathy, ulnar neuropathy at the wrist, and flexor carpi ulnaris exit compression.
Jun. 07, 2021
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This article includes discussion of transient visual loss, cerebral visual loss, monocular visual loss, and visual loss involving central pathways. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.
Clarification of the mechanism and cause of transient visual loss first depends on separating monocular and binocular symptoms and signs. Binocular transient visual loss usually reflects cerebrovascular vertebrobasilar circulation thromboembolism, systemic hypoperfusion, or migraine. Monocular transient visual loss is often attributable to arteriostenotic disease of the internal carotid artery in the cervical or intracranial segment, or stenosis of the ophthalmic artery or its central retinal artery branch. However, reports show that migrainous vasoconstriction and various nonvascular mechanisms are also common causes of monocular transient visual loss and that familial hemiplegic migraine can be associated with multiple daily episodes of transient monocular vision loss in families with SCN1 mutations. Case reports also document that Whipple disease with bilateral optic disc edema and the use of latanoprost for glaucoma have both been associated with transient monocular vision loss in individual patients. In this article, the author cites case reports in which acute glaucoma led to transient vision loss in one or both eyes, which is important for the neurologist to include in the differential diagnosis so that an appropriate ophthalmologic referral can be made in order to prevent permanent vision loss.
• Transient binocular visual loss usually results from cerebrovascular vertebrobasilar circulation thromboembolism, systemic hypoperfusion, or migraine.
• “Reversible posterior leukoencephalopathy” refers to transient cortical binocular blindness with occipital white matter edema that is most commonly associated with acute systemic hypertension and eclampsia or preeclampsia. It has also been associated with various immunosuppressive and cytotoxic drugs.
• Transient monocular visual loss usually results from arteriostenotic disease of the internal carotid artery in the cervical or intracranial segment, or stenosis of the ophthalmic artery or its central retinal artery branch.
The complaint of transient visual loss or simply difficulty seeing can be related to any disorder that temporarily perturbs the afferent visual system. The disorder can affect the eye, retina, optic nerve or tracts, lateral geniculate body, geniculocalcarine tract, or the calcarine visual striate and peristriate cortices. Conditions that affect the oculomotor system can also cause difficulty focusing, double vision, oscillopsia, and other eye movement disorders that compromise binocular vision and are interpreted by the patient as sight difficulties. The alert clinician can usually determine from patient history and examination that these disorders are due to eye movement abnormalities: paresis of movement of an eye muscle, a conjugate gaze or internuclear gaze abnormality, or nystagmus. This article will limit the detailed discussion to disorders that affect visual perception, that is, those that affect the afferent visual system.
Visual loss can be located in 1 eye (monocular) or both eyes (binocular), or may be referable to a portion of 1 homonymous visual field, in which case the defect is detectable in both eyes. In other patients, the disorder is caused by dysfunction of the visual cortex on both sides of the brain, and there is a loss of vision in both eyes and both visual fields. Many patients fail to distinguish between eye and visual field. They have never thought of vision as being brain-related and do not understand the concept of a visual field. Many have not attempted to localize the visual deficit. Because monocular and visual field abnormalities that cause transient visual loss have different clinical manifestations, causes, diagnostic strategies, and treatments, the discussion will be divided sharply between visual loss related to the eyes and visual loss related to the brain and the tracts that connect the eye to the brain.
The clinical importance of monocular visual loss (ie, amaurosis fugax, transient monocular blindness, transient visual obscuration) was described in detail by Miller Fisher (18; 19), who emphasized that transient visual loss in a single eye often provided a clue to the presence of severe occlusive disease of the ipsilateral internal carotid artery in the neck, especially if patients with attacks of monocular visual loss had transient attacks of dysfunction of the contralateral limbs as well. Fisher also described and illustrated the funduscopic findings in a patient that he observed during an attack of transient monocular blindness (17). Pessin and colleagues subsequently showed that nearly all patients who had episodic transient monocular visual loss and transient hemispheric dysfunction referable to the ipsilateral cerebral hemisphere had severe stenosis or occlusion of the ipsilateral internal carotid artery (58).
Bilateral loss of vision referable to the brain (cortical blindness) had been recognized for centuries, but Sir Charles Symonds and Mackenzie deserve credit for demonstrating that the cause was usually infarction of the calcarine visual cortices, most often caused by an embolus that reached the rostral basilar artery and moved into both posterior cerebral arteries (73).
Monocular visual loss.
Symptoms. Transient ocular ischemia is the most common mechanism of transient visual loss (04). Patients usually report negative symptoms. The visual loss is usually described as a graying, blurring, darkening, fogging, obscuring, or dimming of vision in the eye. The visual loss can involve the entire field of vision in that eye, or an altitudinal, lateral, or central sector of vision can be involved in the attack. Some patients describe a shade, blind, or curtain that descends quickly over the eye. Less often, the curtain could ascend or be drawn laterally across the eye; the curtain sometimes creates a uniform line across the vision. In other patients, there is a step in the middle. At times, patients with retinal ischemia describe positive phenomena including scintillations, bright, often colored visual displays, as well as streaks, lines, and shimmers. Miller Fisher's original patient who was examined during an attack of transient monocular blindness “likened the failure of vision to the snowing up of a television screen. . . colorless snowflakes were bright, shining, and jumping. As the cloud took form he could still see through it, but as the cloud became more dense, a total blackout occurred” (17).
In a prospective 4-year follow-up study of 341 consecutive patients with transient monocular blindness, Volkers and colleagues identified the relative risk of various vascular outcome events imparted by specific clinical features of the visual episodes (80). The outcome events occurred in 60 patients and included a subset with ipsilateral ischemic stroke (14 patients) and ipsilateral retinal infarction (6 patients). The clinical features of the vision loss that predicted subsequent ipsilateral vascular events in this subset included (in order of diminishing potency) 1) involvement of only peripheral visual field (not central), 2) constricting onset of visual field loss, 3) downward onset of visual field loss, 4) upward resolution of visual field loss, and 5) more than 3 episodes.
In some patients, transient monocular visual loss is precipitated by standing rapidly, or when blood pressure is excessively lowered by a new antihypertensive drug. In others, the monocular visual loss is precipitated by exposure to bright light. An onset or disappearance of symptoms from above or below (altitudinal), rapid onset within seconds, and duration of 1 to 10 minutes was associated with severe (70% to 99%) ipsilateral internal carotid artery stenosis in 1 study (14). Transient monocular blindness is most common in patients with heterogeneous, hypoechoic plaques that cause severe stenosis (75). When there is tenuous ocular perfusion, exposure of the retina to intense light increases metabolic activity in the retina beyond the perfusion ability of the compromised carotid-ophthalmic artery system.
Signs. The most important and common ophthalmoscopic finding in patients with transient monocular blindness is the presence of embolic particles within retinal arteries. The commonest particles that are seen are cholesterol crystals (Hollenhorst plaques), which are white but may appear bright, often glinting, and yellow-orange in color. These crystals are usually small (10 to 250 micrometers in diameter). They most often lodge at bifurcations of retinal arteries and do not ordinarily block flow. They can move or disappear rapidly but may injure the vascular wall leading to sheathing of the artery. Compressing the orbit may cause crystals to move, flip over, or "flash," making them more visible with the ophthalmoscope. Even when crystals are no longer seen through an ophthalmoscope, fluorescein angiograms may show hyperfluorescent crystals or leakage of dye in regions of arteries damaged by the crystal emboli.
In contrast to cholesterol crystal emboli, platelet-fibrin emboli ("white clots") are longer, gray-white columns that gradually progress through small retinal arteries with distal fragments breaking off as the column moves. Fisher described and drew these white clots as they traversed the retina in a patient with episodes of transient monocular blindness. The third type of embolic material is calcium fragments that appear chalky white and usually remain in 1 location obstructing blood flow (17). Talc, cornstarch, and other foreign body emboli have been described in retinal arteries of patients who inject intravenously mashed-up pills intended for oral use after dissolving the tablets in water.
In some patients, ophthalmoscopy will show branch retinal artery occlusions. Retinal infarcts and focal cotton-wool spots called cytoid bodies that represent retinal microinfarcts are often seen.
Some individuals who have attacks of transient visual loss, especially those whose attacks are induced by exposure to bright light or by orthostatic provocation, have evidence of chronic ocular ischemia. These findings include "venous stasis retinopathy," rubeosis iridis, irregular or fixed pupil, dilated episcleral veins, corneal edema, conjunctival hyperemia, and anterior chamber cells and flare (10). The diagnosis of venous stasis retinopathy is made on the basis of small blot and dot hemorrhages (especially at the mid-periphery of the retina), darkening and dilatation of retinal veins, disc edema, and retinal edema (29; 39).
There are fewer observations of the eye in patients with ocular ischemia related to migraine. The retinal arteries are often narrowed, threadlike, and nonperfused, and the retinal veins may show segmental constriction indicating sluggish or absent blood flow. The optic disc may be pale, visual acuity reduced, or a scotoma found, and the pupil may lose its light reaction during an attack.
In patients with transient visual obscuration caused by increased intracranial pressure, the optic disc is invariably swollen with relatively obvious papilledema.
Optic disc drusen can cause transient and persistent visual loss most often in the form of altitudinal or arcuate defects or centrocecal scotomas (62).
Transient smartphone blindness is a new term that describes transient monocular loss of vision that may happen when using a smartphone in the dark while lying down on one side. Transient smartphone blindness is a benign and physiological phenomenon caused by unequal light adaptation of the afferent visual systems of the two eyes. The eye ipsilateral to the side on which the subject is lying may be blocked from the illumination of the smartphone screen and retains dark adaptation, while the other eye is exposed to the smartphone’s luminance and becomes light adapted. As the subject sets the smartphone aside and starts binocularly exploring the surrounding dark environment, he notices this transient monocular vision loss that lasts for several minutes in the light-adapted eye.
Alim-Marvasti and colleagues reported recurrent transient monocular vision loss consistent with transient smartphone blindness in 2 women 25 and 40 years of age who underwent extensive testing for vascular causes of transient monocular vision loss that included magnetic resonance angiography, echocardiography, and thrombophilia screening (01). Both patients were initially diagnosed with transient ischemic attack and were started on aspirin. Tests were all normal and didn’t show any vascular abnormality. The authors conducted a study in which 2 of the authors monocularly viewed a smartphone screen at arm’s length, and the time course of recovery of sensitivity in the dark was quantified both psychophysically and electrophysiologically by means of electroretinography. Visual sensitivity was appreciably reduced after smartphone viewing, taking several minutes to recover. Irshad and Adhiyaman reported 2 similar cases--a 25-year-old man and 36-year-old woman, both of whom were diagnosed by their primary care practitioners as having transient ischemic attacks (35).
Sathiamoorthi and Wingerchuk also reported another case of transient smartphone blindness in a 58-year-old female patient who underwent extensive laboratory and imaging work-up. The patient was diagnosed with multiple sclerosis based on associated nonspecific white matter lesions in her brain MRI scan. Disease-modifying therapy was recommended. Review of the history with the patient 6 months later shifted the diagnosis towards transient smartphone blindness (68).
Although any history of transient monocular vision loss should be taken seriously, careful history taking can help avoid unjustified risk and expense in addition to the psychological consequences of unnecessary testing and treatment if this new modern-day cause of transient monocular vision loss is recognized.
Visual loss involving central pathways. Involvement of the optic chiasm, optic tract, lateral geniculate body, geniculocalcarine tract, and striate cortex can cause visual loss that is usually persistent, but occasionally transient, involves both eyes, and most often affects homonymous visual fields.
The most common symptom is transient hemianopic visual loss. Some patients describe positive phenomena within the visual field (ie, spots, stars, lines, circles, fortifications), or less often, forms of inanimate objects, animals, and people. There may be simply a void to 1 side or the other, darkness, or grayness. Some patients are unaware of the visual field defect and are accident-prone because of this ignorance. When the visual field defect is bilateral and severe, cortical blindness results.
The most important finding in patients during visual loss is a visual field defect. The pupils invariably react normally to light unless the lesion involves the optic tract, in which case a Wernicke hemianopic pupil may be found. Homonymous scotomas can be found. In some patients, elements of Balint syndrome (simultagnosia, optic ataxia, optic apraxia) are found on examination (08). Abnormalities in reading; color recognition and naming; face identification; revisualization of objects, people, and directions; and comprehension and conveyance of language may accompany the visual field defects (08). Visual neglect, abnormal optokinetic nystagmus, and poor drawing and copying are sometimes found.
Seizures. Seizure discharges from the posterior parietal, posterior temporal, and occipital lobes can give rise to temporary visual symptoms and transient hemianopia. Positive visual phenomena are the rule, but in some patients a transient hemianopia results. Tumors and vascular malformations are the most common cause of occipital lobe seizures. In a study of 43 patients with posterior cortical epilepsy, Yu and colleagues found that 4 patients had visual aura described as blurry vision, whereas 14 had “elementary visual hallucinations,” and 4 had “visual illusions.” None described transient visual blackouts (87).
Prognosis depends on the etiology of the transient visual loss and the treatment of the causative condition.
Case 1. A week prior to presentation, a 75-year-old man noted a black shade descend over his right eye for about 30 seconds, with the shade lifting from the bottom up. He had a past history of hypertension and coronary artery disease as well as coronary artery bypass surgery and claudication of the right leg when he walked. Two days prior to presentation, he noted clumsiness and weakness of his left hand for 3 minutes. He had been having headaches, which were unusual for him, during the past 3 weeks.
Examination showed a loud, long, high-pitched right carotid artery bruit. A bright cholesterol crystal was seen in his right eye at a bifurcation point distally along a superior retinal artery. His neurologic exam, visual acuity, and visual fields were normal.
Duplex sonography showed a severe stenosis of his right internal carotid artery, a finding corroborated by CT angiography of the neck. CT showed no brain infarction. He had an uneventful right carotid endarterectomy.
Case 2. A 38-year-old woman suddenly became agitated and restless. No prior history was available. On examination it became apparent that she could not see. She also could not recall information given to her moments before. Pupillary light responses and funduscopic examination were normal, as was the remainder of her neurologic examination.
MRI scan after sedation showed bilateral infarcts in the occipital and temporal lobes in the distribution of the bilateral posterior cerebral arteries. Transthoracic echocardiogram showed a large myxoma in the left atrium. She had cardiac surgery to remove the myxoma.
Monocular vision loss. The known mechanisms of transient visual loss can be divided into 3 main groups: embolism, hypoperfusion, and retinal angiospasm (06). At times, mechanical, serological, hemodynamic, and hematological factors contribute to these mechanisms.
Cerebral visual loss. The major causes are ischemia due to (1) atherosclerotic disease of the intracranial posterior cerebral, anterior choroidal, and middle cerebral arteries; (2) embolism to these arteries; and (3) migraine. Seizures can also cause transient central visual loss.
Common causes of monocular visual loss.
Atherosclerotic occlusive disease of the common carotid artery. Transient monocular blindness may be more prone to occur when occlusive disease involves the common carotid artery than when it involves the internal carotid artery (4 of 8 symptomatic cases of common carotid artery disease vs. 9 of 137 symptomatic patients with internal carotid artery stenosis) (33). Hoya and colleagues postulate that hemodynamically significant flow reduction in both the internal and external carotid arteries underlies a propensity for retinal ischemia with common carotid artery disease. The relative incidence of internal carotid disease is, however, much greater than that of common carotid artery disease.
Atherosclerotic occlusive disease of the internal carotid artery in the neck. The most important etiology of transient monocular blindness is occlusive carotid artery disease in the neck. Patients with severe internal carotid occlusive disease with less than 1 mm residual lumen (90% stenosis) often have relatively frequent brief attacks of dimming of vision in the entire visual field of the ipsilateral eye. The attacks may be brought on by standing up quickly. Occasionally, patients with severe internal carotid artery occlusive disease in the neck may have attacks of brief, transient, monocular blindness brought on in relation to neck position (eg, during archery or violin playing). Some patients with severe carotid artery stenosis develop repeated attacks after eating (48). Patients with plaque disease that causes less severe stenosis more often have isolated infrequent episodes of loss of vision in a part of the visual field correlated with emboli to branch retinal arteries. When the internal carotid artery is completely occluded, patients may show periodic dimming of vision when exposed to bright light. Occasional patients with bilateral internal carotid occlusive disease have had bilateral dimming of vision on bright light exposure (38). Some patients who have had attacks of transient monocular blindness when their internal carotid arteries were stenotic stop having the attacks when the internal carotid artery fully occludes. Monitoring of the ipsilateral middle cerebral artery (using transcranial Doppler ultrasound) in patients with transient monocular blindness related to severe carotid stenosis shows many high-intensity transient signals that represent microemboli emanating from carotid plaques (71; 82; 15). After the internal carotid artery occludes, microemboli diminish and soon are no longer detectable by transcranial Doppler. These same patients with carotid artery occlusion may have a recurrence of their transient monocular blindness when the contralateral external carotid artery, which is the main collateral artery supply of the eye, becomes stenotic or occluded.
Atherosclerotic disease of the internal carotid artery is most common in white men. White men with atheromatous carotid artery occlusive disease also have a high frequency of hypertension, hyperlipidemia (high LDL cholesterol and low HDL cholesterol), coronary artery disease, and peripheral vascular occlusive disease with claudication of the legs. Women and individuals of Asian and African American origin have a lower frequency of carotid artery occlusive disease in the neck. Occasionally, other occlusive lesions (ie, Takayasu arteritis) can cause transient monocular visual loss (72; 52).
Internal carotid artery dissection in the neck. Acute carotid artery dissections usually involve the artery within its pharyngeal segment, above the carotid bifurcation and below penetration of the artery into the cranium. The dissections can be caused by direct trauma but most are called spontaneous; they are likely precipitated by stretching or pulling movements that tear the wall of the artery. When the artery becomes acutely narrowed or occluded, patients often have episodes of transient monocular visual loss as well as spells of transient ipsilateral hemispheric ischemia. The episodes are often brief but repeated over a short period of time ("carotid allegro") and are likely caused by decreased ophthalmic artery blood flow.
Occlusive disease of the intracranial carotid artery in the carotid siphon and intracranially. Disease of the internal carotid artery in the siphon proximal to the ophthalmic artery origin can also give rise to attacks of monocular visual loss. In Chinese and other patients of Asian origin, stenotic lesions of the intracranial carotid artery are as common as those in the neck as causes of transient monocular visual loss (34). Sometimes the cause is an aneurysm that harbors a clot. The aneurysm may lie within the cavernous sinus and cause cranial nerve signs. Most patients with carotid artery siphon stenosis and those with aneurysms have a high frequency of hypertension.
Stenosis of the ophthalmic artery: atheromatous and arteritic. The frequency of atheromatous occlusive disease of the ophthalmic artery as a cause of episodes of transient monocular visual loss is unknown. Such a case is provided by Park and colleagues with angiographic demonstration of the ophthalmic artery stenosis and discussion of proposed mechanisms (56). Some diabetic patients develop intrinsic ophthalmic artery disease. Giant cell arteritis is probably the most frequent cause of ophthalmic artery disease but most such patients have persistent rather than transient monocular visual loss.
Migraine. Occasional patients with migraine have attacks of visual loss that are monocular. These are usually described as graying or blurring of vision; sometimes a gray or white curtain covers vision. Descriptors of the visual loss are not different from those used by patients with carotid artery occlusive disease and are distinct from the bright scintillations of occipital migraine. Most patients have had complete loss of monocular vision rather than altitudinal symptoms (84; 83). Some have had aching or discomfort in the eye during attacks. Attacks can be frequent and occur more than once a day. Observation of the ocular fundus in patients with vasospastic transient monocular blindness usually shows constricted retinal arteries and rouleaux formation in veins in relation to slowed blood flow. The arteries may appear threadlike and the optic disc may look pale (07; 84; 83).
Not all monocular migrainous auras are, however, clearly vasospastic. Robertson, an ophthalmologist, provided a useful personal account of his own binocular migrainous auras and monocular “retinal” migraines spanning several decades. Retinal examination during 1 monocular episode did not reveal any vascular spasm, which suggested to him that spreading depression might be the mechanism of some monocular episodes. Amsler grid charts of what Robertson described as absolute monocular scotomas were remarkably similar in recurrent episodes over many years – the extent, shape, and position of the scotoma were the same each time (66).
Most patients with evidence for retinospastic transient monocular blindness do not meet standardized criteria for diagnosis of migraine and should be classed simply as vasospastic amaurosis fugax or transient monocular blindness (30). Vasospastic transient monocular blindness is most common in relatively young women but also occurs in men (21; 26). Some patients have clustering of attacks that can occur many times a day (60). Patients with systemic lupus erythematosus have vasospastic transient monocular blindness (70). Vasospastic transient monocular blindness has also been described as occurring repeatedly in a patient during sexual intercourse (76) and after vigorous exercise (37). Drugs such as phencyclidine and cocaine can also trigger vasospastic transient monocular visual loss (78). Transient monocular visual loss can also develop during hypertensive crises and eclampsia presumably related to vasoconstriction of retinal, ciliary, and choroidal arteries (77). Some patients with vasospastic transient monocular visual loss also have Raynaud phenomenon (20), and a number of conditions, such as parathyroid adenoma, can cause retinal secondary vasoconstriction (20). Prescription of calcium channel blocking drugs has been reported to prevent these attacks (84; 83).
Embolism from the heart. Occasional patients with disorders of the heart that promote systemic and brain embolism will have an attack of transient monocular blindness (09). It is, however, unusual for patients with cardiogenic embolism to have repeated attacks of visual loss. Mouradian and colleagues found a cardiac or aortic potential embolic source among 16 of 73 patients (22%) who had retinal ischemia (53).
A variety of different cardiac conditions including mural thrombi, hypokinetic segments, cardiac aneurysms related to coronary artery disease, myocarditis and myocardiopathy, cardiac tumor, atrial fibrillation, paradoxical embolism, and valvular heart disease can lead to ocular and brain embolism (09). In patients with systemic lupus erythematosus and the antiphospholipid antibody syndrome, transient monocular visual loss is most often due to emboli from fibrous valve disease (Libman-Sacks type), but migraine is also common (22). However, retinal embolism and transient monocular visual loss is more common in patients with carotid stenosis than in patients with atrial fibrillation (03).
Atheromatous embolism usually arising from the aorta. The aorta has been recognized as an important source of embolism, especially during and after cardiac surgery. Angiography of the aorta and coronary circulation can also precipitate atheromatous embolism. Patients may have repeated attacks of transient monocular blindness after coronary or other angiography. Cholesterol crystals may be seen within retinal arteries. Renal dysfunction, ischemia of the digits of the hands and toes, and muscle pain and tenderness are frequent accompanying symptoms. Most patients with embolism arising from the aorta have atheromatous, often protruding plaques that can be seen on transesophageal echocardiography. Most plaques are located in the curvature of the aortic arch from the distal ascending aorta to the proximal portion of the descending aorta. These plaques can also be shown by duplex sonography using supraclavicular windows (81). Occasional patients with aortic trauma, aortic dissection, and Takayasu disease have emboli to the eye arising from the aorta.
Increased intracranial pressure in patients with pseudotumor cerebri. Patients with pseudotumor cerebri (benign intracranial hypertension) have transient visual obscuration (51). These are often monocular but can be binocular. The episodes are usually brief and often are precipitated by coughing, straining, or other maneuvers that elevate intracranial pressure. Prominent headaches are invariably associated (12). The mechanism is presumed to be insufficient arterial perfusion to surmount the increased intracranial pressure, which causes increased pressure in retinal veins. The arterial and venous difference becomes insufficient to perfuse the retina, especially when retinal vein pressure rises. The same mechanism probably occurs in patients with glaucoma and cavernous sinus arteriovenous fistulae and extensive dural sinus thrombosis (23; 54).
Unusual and rare causes. A number of unusual disorders can cause transient monocular visual loss or bilateral visual loss attributable to the retinal circulation. Some common causes of persistent visual loss on unusual occasions also cause transient visual loss. Iridoplegia and dilated pupils, eg, in relation to a migraine attack, can cause visual dysfunction that is temporary.
Familial hemiplegic migraine with SCN1A mutation has been found to occur together with a highly stereotyped form of transient monocular vision loss in several members of 2 families (79). The vision loss lasts between 3 and 10 seconds; it can occur spontaneously but is often elicited by rubbing the eye, sudden exposure of the eye to bright light, or standing up quickly – presumably from transient hypotension and ischemia. Vision loss can occur in both eyes after rubbing just 1 eye with a 1- to 2-second delay before onset in the second eye (45). During an episode, the pupil is dilated and unresponsive to light. The fundus appearance has not been observed during an attack. One theory holds that these episodes represent spreading depression in the retina rather than ischemia or vasospasm because they typically occur multiple times daily for decades without resulting in permanent vision loss (79).
Patients with ischemic optic neuropathy, the arteritic and nonarteritic forms, can occasionally have an attack of reversible visual loss. Detachment of the retina can rarely manifest as transient loss of vision. Glaucoma and vitreous and aqueous humor abnormalities (hemorrhages, infections, neoplasms) can rarely cause acute transient visual loss invariably accompanied by other ocular symptoms and signs. The uveitis-glaucoma-hyphema syndrome is an unusual cause of transient monocular visual loss that can follow cataract extraction and intraocular lens implantation. Patients with this disorder often have reddening of vision, an ache in the eye, and hyphemia with signs of an anterior uveitis and raised intra-ocular pressure (11). Central retinal vein occlusion can sometimes be preceded by episodes of transient monocular visual loss. Transient visual loss can occur in an eye after a variety of different surgical procedures on that eye. Hyphemia after intraocular surgery can cause temporary visual loss (36; 02). Transient visual loss can also occur after sub-Tenon anesthesia given for cataract surgery (16; 40). Transient monocular visual loss has also been reported after deep sclerotomy (02) and in patients with leaking blebs following trabeculectomy for glaucoma (25).
Systemic disorders that cause hypercoagulability and hyperviscosity such as polycythemia vera, thrombocytosis, and Waldenstrom macroglobulinemia can cause sluggish retinal artery blood flow that can give symptomatic transient visual loss. Hypercalcemia caused by hyperparathyroidism and ingestion of large amounts of licorice (13) can give rise to retinal artery vasospasm and cause transient visual dysfunction in 1 or both eyes. Tumors of the orbit and cavernous angiomas within the orbit can cause visual loss that is transient and often gaze evoked (41). Optic disc drusen can occasionally cause transient visual loss and anterior ischemic optic neuropathy (62). The neuro-ophthalmologic form of sarcoidosis characterized by sheathing of retinal veins, candle dripping retinal exudates, and granulomas of the optic nerve have also been known to cause temporary episodes of visual loss. Preretinal arterial loops that extend into the vitreous arise from the central retinal artery (65). These loops are often kinked and flow can become temporarily or persistently diminished within the loop causing transient loss of a portion of monocular vision. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), a disorder of cerebral penetrating arteries, can occasionally involve the retinal and choroidal arteries, causing transient or persistent monocular visual loss (67). Some patients with retinal inflammatory disorders such as Lyme disease and cat-scratch disease may report transient visual blurring and visual loss (42; 64). One patient report describes a patient who had transient bilateral visual loss of presumed ocular origin after unilateral electric shock therapy for bipolar disease (43).
A patient with Whipple disease (Tropheryma whippelii) presented with transient visual obscurations in the presence of severe bilateral optic disc edema and later had retinal vasculitis (69).
A 59-year-old man with primary open-angle glaucoma started having left-eye total vision loss (no light perception) on first waking in the morning (lasting 2 hours) 6 weeks after adding latanoprost to a treatment regimen that included timolol and dorzolamide. After this happened once, he omitted latanoprost, and no vision loss occurred the next morning. He then resumed taking latanoprost intermittently, and episodes of left-eye vision loss recurred the next morning after each dose but not on the mornings after he omitted the drug. Vasoconstriction in previously compromised circulation in the left eye was deemed the most likely cause by the authors (49).
A 59-year-old woman started having episodic binocular visual blurring 2 days after a third epidural steroid injection for herniated lumbar disc, and it was determined that she was having intermittent glaucoma with elevated intraocular pressure (50). The episodes resolved spontaneously within 3.5 months without the addition of pressure-lowering eye drops. A 51-year-old man started having episodes of transient monocular right eye visual loss lasting 20 to 30 minutes, with onset uniformly 10 to 15 minutes after sexual intercourse (46). His intraocular pressures were normal on exam when he was asymptomatic, but he was found to have narrow angles on gonioscopic exam of the anterior segments of each eye, which is the substrate for acute glaucomatous attacks. Laser peripheral iridotomy was performed on both eyes, and he remained free of symptomatic episodes for 6 years of follow-up thereafter.
Gaze-evoked transient monocular vision loss has been seen in the presence of intraconal orbital masses, most commonly meningioma or hemangioma (05; 55). A rare instance of gaze-evoked monocular visual loss was reported in a patient with an orbital metastasis, in this case from a primary breast carcinoma (57). Another rarely reported cause of gaze-evoked transient monocular blindness is Churg-Strauss vasculitis (27).
Common causes of cerebral visual loss.
Atherosclerosis of posterior circulation arteries. Severe stenosis or occlusion, or less often, dolichoectatic dilatation of the intracranial vertebral or basilar arteries can cause intermittent decrease in blood flow to the occipital lobes, so that patients describe transient loss of vision or frank blindness. These patients also often have attacks of dizziness, diplopia, limb weakness, ataxia, and other symptoms indicative of brainstem dysfunction. Stenosis involving both of the intracranial vertebral arteries is the lesion most often likely to cause attacks of bilateral visual loss (08). Some patients have severe stenosis of the distal basilar artery that causes attacks of bilateral visual loss.
Patients with stenosis of 1 posterior cerebral artery may have transient ischemic attacks that include transient hemianopic visual abnormalities (59; 08). They may report scintillations or brightness, but more often note temporary lack of vision in the visual field contralateral to the stenotic posterior cerebral artery. In some patients, the hemivisual abnormality is accompanied by paresthesias or numbness on the side of the body where visual loss occurs. The most common cause of posterior cerebral artery territory infarction is embolism to the posterior cerebral artery from the heart, aorta, or extracranial and intracranial vertebral arteries (08; 85). Sometimes embolism to the posterior cerebral artery causes only transient hemianopic visual loss.
Occlusion of the anterior choroidal artery can cause ischemia of the optic tract, lateral geniculate body, and the proximal portion of the geniculocalcarine tract. Most often the hemianopic visual loss that results is persistent and consists of a homonymous hemianopia, an upper quadrantanopia, or a homonymous sectoranopia involving the upper and lower quadrants but sparing the horizontal meridian. A hemiparesis and hemisensory loss often accompanies the visual field loss. Occasionally, the hemianopic visual loss can be temporary. Although infarction in the territory of the middle cerebral artery can cause a hemianopia and visual neglect, it never causes a temporary hemianopic visual loss.
Migraine. Migraine is undoubtedly the commonest cause of transient visual loss on a CNS basis. Attacks usually last from 15 to 30 minutes. Most often, the attack begins with a small formed object or objects. The objects vary greatly; stars, circles, squares, zigzags, pointed lines, fire-flies, lightning bolts, heat waves, pinwheels, rods, and beads are just a few of the descriptors that patients give to the forms. Sometimes the forms are linear and have angles and straight edges. An early migraineur described his aura as consisting of lines that looked like a fortified town with bastions. The resemblance of the edges and lines to forts led to the frequent use of the term "fortifications" and fortification spectra to describe this type of visual experience. Often the forms are bright and may be colored, especially red, green, blue, extra-white, or purple. Migraineurs usually describe some type of motion, both in-place and across the visual field. Motion in-place is often described as flickering, shimmering, rotating, oscillating, or like a kaleidoscope. A key feature of the visual symptoms is build-up of the visual forms. The forms often become brighter, larger, or more objects may appear with time, and the objects usually gradually move across the visual field.
Characteristically, the forms move slowly across the visual field, leaving in their wake a void or darkness (ie, scotoma). Often as the forms move, the scotoma enlarges.
In some patients, the predominant symptom is loss of vision without illusory forms. This can take the form of a black spot but more often the visual loss is that of a hemianopia. Altitudinal or quadrantic visual field defects occur occasionally but are less common than hemianopic defects. The visual field loss is usually binocular and similar in the 2 eyes. It may begin abruptly or progress during minutes. A case of migrainous right homonymous hemianopsia was documented using frequency doubling technique, and residual partial right homonymous defect was mapped using static threshold perimetry 4 hours later (24). Repeat threshold testing 1 week later showed nearly complete resolution of the right homonymous visual field defect. Total obscuration of vision with dimness or blackness is also common. Sometimes the attacks of blindness last seconds to 10 minutes or more and may be repeated. In some, dimness or black spots gradually spread. In others, blindness has a sudden onset as if someone shut off the lights in an instant.
Rare patients have had visual distortions or metamorphopsia as a manifestation of their migraines.
Uncommon causes of cerebral visual loss.
“Reversible posterior leukoencephalopathy” refers to temporary cortical blindness, altered mental state, seizures, headache, and other focal neurologic deficits associated with vasogenic edema without infarction in the occipital-parietal white matter. It typically accompanies acute hypertension, as in eclampsia or preeclampsia (31), but is also encountered in other hypertensive states such as acute glomerulonephritis or hemolytic-uremic syndrome or secondary to immunosuppressive drugs, especially the calcineurin inhibitors cyclosporine and tacrolimus (47; 32). Lee and colleagues reviewed 38 episodes of posterior reversible encephalopathy syndrome at the Mayo Clinic and found the following comorbidities in the group: hypertension in 53%, kidney disease in 45%, dialysis dependency in 21%, and bone marrow or solid organ transplantation in 24%. Sixteen percent were also alcoholic, and 32% had some form of cancer. Symptoms included clinical seizures in 87%, seizures with focal onset in 26%, encephalopathy in 92%, visual loss in 39%, and headache in 53%. Clinical recovery occurred in a mean of 5.3 days with a range of 0 to 32 days. The MRI characteristic of vasogenic edema is high-signal intensity on T2-weighted and fluid-attenuated inversion recovery (FLAIR) images along with isointensity in diffusion-weighted images and high-signal (bright) in apparent diffusion coefficient (ADC) maps (47). MRI abnormalities are not restricted to the posterior hemisphere white matter and are not infrequent in the frontal lobes, basal ganglia, thalami, cerebellum, and brainstem, as well as in cerebral cortex. Although the reversibility of the syndrome has been attributed to the presence of mainly vasogenic edema, as opposed to cytotoxic edema, Yilmaz and associates presented a case of posterior reversible encephalopathy syndrome in a 9-year-old boy on tacrolimus after liver transplant in which the MRI showed evidence of cytotoxic edema (increased signal on diffusion-weighted imaging), and there was still good reversibility of clinical abnormalities after discontinuation of the drug (86). The authors emphasize that an MRI showing evidence of cytotoxic edema should not be used to rule out the diagnosis of posterior reversible encephalopathy syndrome in the setting of drug toxicity. Rao and coworkers described a case of reversible posterior encephalopathy in a patient with cystic fibrosis, status post 2 lung transplants, on tacrolimus in whom right homonymous hemianopsia and seizures were precipitated immediately after saline flushing of a peripherally inserted central catheter (PICC line) that had been erroneously inserted into the left internal jugular vein instead of the left atrium. The authors cite this case as evidence that a primary feature in the etiology of posterior reversible encephalopathy is increased venous pressure leading to cerebral vascular autoregulatory failure and vasogenic edema (63).
A study of 2398 patients with suspected transient ischemic attacks presenting to a French stroke center included 826 patients with transient visual symptoms. The most frequent visual symptom was transient monocular blindness (36.3%), followed by diplopia (13.4%), homonymous hemianopsia (12.3%), bilateral positive visual phenomena (10.8%) and lone bilateral blindness (4.5%). Positive diffusion-weighted MRI was most often abnormal in patients with homonymous hemianopsia (11.8%). In a subset analysis of 1850 patients with transient ischemic attack, the 595 patients with isolated transient visual symptoms had an identifiable source for emboli (19.6%) than those with other transient symptoms (28.1%, P< 0.001). Patients with homonymous hemianopsia had a higher rate of atrial fibrillation (23.2%) than the patients with other transient visual symptoms (4.0%) or nonvisual transient symptoms (9.1%) (44).
Monocular vision loss. Epidemiology depends on the cause. Atherosclerosis of the internal carotid artery and migraine are common. The other causes are more unusual.
In a retrospective review of 464 patients seen at 13 collaborating stroke centers in Japan with transient ischemic attack (TIA), 13 patients with transient monocular blindness (TMB) were compared with the other TIA patients. Patients with TMB were more likely to have internal carotid artery stenosis (33% vs. 9.1%, P=.022) (74).
Hayreh analyzed the frequency of transient monocular blindness in patients with various intraocular vascular disorders, including 271 with central retinal artery occlusion (12.18%), 169 with branch retinal artery occlusion (14.20%), 39 with ocular ischemic syndrome (15.38%), 864 with central retinal vein occlusion (37.84%), 67 with hemi-central retinal vein occlusion (13.43%), 864 with branch retinal vein occlusion (0.35%), 964 with non-arteritic anterior ischemic optic neuropathy (2.54%), and 147 with giant cell arteritis and vision loss (32.4%) (28).
A retrospective analysis was carried out on 77 patients with nonembolic transient monocular blindness at Moorfield’s Eye Hospital in London. The mean age at onset was 37 years (14 to 77). Five percent had attacks alternating eyes, the rest occurred in one eye only. Twelve percent had a past history, and 8% had a family history of migraine. Headache followed the visual attacks in 14%. Vision loss was permanent in 3 patients who did not have headache. Nifedipine treatment of 13 patients with more than one attack per week reduced the attack frequency in all, suggesting a vasospastic etiology (61).
Cerebral visual loss. This depends on the cause. Atherosclerosis of the internal carotid artery and migraine are common. The other causes are more unusual.
Prevention of both monocular and cerebral visual loss depends heavily on etiology and mechanism. This has been described above.
Testing, of course, must be individualized. For transient monocular visual loss, a thorough ophthalmologic exam is always important. Blood tests are often important and include (1) sedimentation rate, (2) serum calcium, (3) complete blood count including a platelet count, and (4) serum lipid analysis. In some patients antinuclear antibodies and tests for systemic lupus erythematosus are appropriate.
Most important in adult patients with atherosclerotic risk factors is imaging of the internal carotid artery in the neck and intracranially. The internal carotid artery in the neck can be studied using (1) duplex ultrasound of the neck, (2) magnetic resonance angiography, (3) CT angiography, or (4) standard catheter dye angiography. The intracranial internal carotid artery can be studied using CT angiography, magnetic resonance angiography, standard catheter angiography, and transcranial Doppler ultrasound. The ophthalmic artery can be studied using color-flow Doppler examination of the orbit. Transcranial Doppler ultrasound monitoring of patients with retinal ischemia often documents the presence of microemboli emanating from the heart, aorta, or carotid arteries (82).
In patients suspected of having temporal arteritis, B-mode examinations of the superficial temporal arteries and temporal artery biopsy are often diagnostic.
Echocardiography, especially transesophageal, can show cardiac and aortic sources of embolism to the eye.
Workup for visual loss of CNS origin should include, in most patients, a brain image (CT or MRI) as well as vascular studies of the posterior circulation arteries. B-mode ultrasound and color-flow Doppler can provide good images of the proximal vertebral arteries in the neck. The Doppler probe can explore the neck to determine the direction (anterograde or retrograde of flow in the remainder of the extracranial vertebral arteries). Transcranial Doppler gives accurate information about occlusive disease of the intracranial vertebral arteries. Magnetic resonance angiography and CT angiography as well as standard dye contrast catheter angiography allow imaging of both the extracranial and intracranial posterior circulation arteries. Electroencephalography is often useful when seizures are suspected.
Treatment depends much on the cause. For persisting monocular vision loss, ocular massage, carbon dioxide inhalation, acetazolamide, inhaled isuprel, and sublingual nitroglycerin all have been advocated with variable success. In some patients with ophthalmic artery occlusion, intra-arterial thrombolysis has been used. When the internal carotid artery is tightly stenotic, carotid endarterectomy and angioplasty with stenting are possible treatments. Temporal arteritis is usually treated with high-dose corticosteroids.
Clearly, treatment depends heavily on the cause of the CNS symptoms. Antiplatelet aggregates, standard anticoagulants (heparin and warfarin), surgery in the form of endarterectomy or bypass, and angioplasty with stenting have all been used to treat occlusive posterior circulation disease (08). Various prophylactic agents are used to prevent migraine and seizures.
Eclampsia can cause monocular visual loss and cortical blindness in relation to the development of vasoconstriction within the eye and a posterior leukoencephalopathy within the brain (31; 77).
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