Headache & Pain
Neuroimaging of headache
Dec. 02, 2023
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Transient visual loss, meaning vision loss that resolves spontaneously within 24 hours, can have causes ranging from benign to emergent and potentially catastrophic, making proper evaluation urgent. Any disorder that can cause temporary dysfunction of the afferent visual system, including the eye, retina, optic nerve or tracts, lateral geniculate body, geniculocalcarine tract, or calcarine visual striate and peristriate cortices, can cause transient visual loss. As the vision loss is transient, the examination is often unrevealing, making the history particularly essential for diagnosis.
Differentiating monocular and binocular symptoms is the first step toward identifying the etiology. Binocular transient visual loss may be due to posterior circulation ischemia, migraine visual aura, or seizure. Monocular transient visual loss may be due to thromboembolism or vasospasm of the central retinal artery, ocular causes such as acute angle closure glaucoma and pigmentary dispersion syndrome, or other causes, including migraine visual aura.
For the purposes of this review, transient vision loss refers to relatively brief (hours or shorter) episodes of transient visual loss or transient visual disturbances that resolve spontaneously. Causes of vision loss that are reversible by treating the underlying cause, such as posterior reversible encephalopathy syndrome and hyperglycemic nonketotic homonymous hemianopia, are outside the scope of this review. Conditions that affect the efferent visual system, meaning the oculomotor system, may also cause transient or intermittent visual symptoms, including difficulty focusing, double vision, and oscillopsia, but this article focuses on disorders that cause a transient change to the afferent visual system.
• Transient binocular visual loss may be due to posterior circulation ischemia, migraine, or seizure.
• Transient monocular visual loss may be due to thromboembolism or vasospasm of the central retinal artery; giant cell arteritis; papilledema; ocular causes, such as acute angle closure glaucoma; or other causes, including migraine.
• The most important job of the clinician is to identify and protect the patient from dangerous causes of transient vision loss (ischemic, arteritic, angle closure glaucoma, papilledema).
The clinical importance of transient monocular visual loss was initially described in detail by C Miller Fisher (20; 21; 16), who emphasized that transient visual loss in a single eye may occur due to thromboembolism from severe occlusive disease of the ipsilateral internal carotid artery in the neck. Associated episodes of contralateral hemibody weakness are also suggestive of thromboembolic events due to carotid stenosis. Fisher also described and illustrated the funduscopic findings in a patient that he observed during an attack of transient monocular blindness (18). Pessin and colleagues subsequently showed that a high percentage of 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 (48).
The term “amaurosis fugax,” Greek for “swift, transient, or fleeting darkness,” is sometimes used as a synonym for transient monocular vision loss, specifically transient monocular vision loss due to a thromboembolic cause. Some providers may use it as a description of undifferentiated symptoms, and others may assume that it means that a thromboembolic cause has already been confirmed. Given these different usages, this term is imprecise and can mistakenly imply to other providers that an ischemic etiology has been confirmed; thus, it is best avoided (19; 07; 42).
• Localization starts with distinguishing whether a transient visual loss event was monocular or binocular.
• Taking a detailed history of the event is a key part of diagnosis.
• Evaluation requires a thorough ophthalmic examination, including ocular surface examination; evaluation of the depth of the anterior chamber; and evaluation for optic disc swelling, retinal emboli, and cotton wool spots, as well as for any focal neurologic signs.
Monocular and binocular visual loss have different localizations. Monocular vision loss localizes to the eye or the anterior visual pathways, whereas binocular vision loss localizes to the chiasm or retrochiasmal visual pathways. Thus, they require different diagnostic strategies. Additionally, some causes of transient vision loss are monocular phenomena that commonly affect both eyes simultaneously, such as transient visual obscurations and dry eye (Table 1).
Providers must be cognizant that patients may not accurately identify the localization of an episode of transient vision loss. For example, a right hemifield defect affecting both eyes may be described by the patient as vision loss affecting the right eye. During the event, many patients will not have attempted to localize the visual deficit, which is best done by covering one eye and then the other. In cases of ongoing vision loss, examination maneuvers, such as visual acuity testing, color vision testing, the swinging flashlight test, and visual field testing, allow providers to distinguish between monocular and binocular vision loss. However, in cases of transient vision loss, the patient’s history may be the sole source of diagnostic information. Historical clues that can suggest that a transient vision loss event affected both eyes include difficulty reading (which should not be seen in patients with monocular vision loss) and noticing a respect of the vertical.
Transient monocular vision loss
Monocular phenomena that may affect both eyes simultaneously
Transient binocular vision loss
Ischemic (embolic, hypoperfusion, venous congestion, giant cell/temporal arteritis)
Transient visual obscurations
Migraine visual aura
Central retinal artery vasospasm
Transient intraocular pressure elevations
Posterior circulation transient ischemic attack
Orbital mass (“gaze-evoked amaurosis”)
Dry eye or ocular surface
Occipital lobe seizure
Smartphone amaurosis/transient monocular vision loss on awakening
Transient monocular vision loss on awakening
Additional ocular causes, such as vitreomacular traction, hyphemia, postsurgical complications
Further, pinpointing the etiology depends on taking a careful, detailed history to elucidate the character of the vision loss episode or episodes (Table 2). However, the patient’s description alone may not allow the physician to determine the cause (07). It is important to have a low threshold and consider arteritic and ischemic causes in order to protect patients from permanent vision loss and other complications.
• One eye or both eyes?
• How did the vision loss onset (sudden versus gradual)?
• How did the vision loss evolve?
• Pattern and degree of vision loss (blackout versus blur, respect of vertical, horizontal)
• Positive visual phenomena
• Duration of each individual episode (how long does each episode last?)
• Duration of overall symptoms (how long ago did the episodes start?)
• Triggers/provoking factors (positional changes, bright lights, exercise, head, eccentric gaze)
• Associated symptoms (focal neurologic symptoms, systemic symptoms of giant cell arteritis)
• Relevant past medical history (vascular risk factors, recent surgeries)
Transient monocular vision loss occurs due to pathology affecting the anterior visual pathways, including the prechiasmal optic nerve, retina, and other ocular structures. Even after determining that an episode of transient vision loss is monocular, the differential diagnosis remains broad, including ischemic causes, ocular causes, and migraine (Table 1). The most common cause of transient monocular vision loss is ischemia (07).
Embolic occlusion of central or branch retinal artery. Ischemic transient monocular vision loss can represent a transient embolic occlusion of the central retinal artery or a branch retinal artery, particularly thromboembolism from carotid disease (63).
This type of transient monocular vision loss is expected to be sudden-onset, painless vision loss and is classically described as a dark “shade,” “curtain,” or complete blackout of vision lasting 1 to 4 minutes. Patients may also describe an altitudinal cut-off or a “line” in their vision. Ischemia is not typically expected to cause frank positive visual phenomena, but patients with retinal ischemia occasionally describe shimmering or whiteness, such as “Autumn mist” (author’s own case files) or “snowing up of a television screen” (18). Examination showing retinal emboli can be supportive of a diagnosis of embolic occlusion, but a normal fundus examination does not rule it out.
Ischemic transient monocular vision loss can also be described as a retinal transient ischemic attack and is a cerebral stroke/transient ischemic attack equivalent. In fact, 20% to 30% of patients who present with transient monocular vision loss have acute silent strokes on diffusion-weighted imaging (28; 56; 06; 04). A full stroke work-up, including urgent carotid imaging, is appropriate. If recent, emergency department or inpatient work-up may be appropriate (06).
Neck pain and ipsilateral Horner syndrome should raise suspicion for carotid dissection as thromboembolism from a carotid artery dissection may cause monocular vision loss.
Giant cell arteritis or temporal arteritis. Giant cell arteritis (also known as temporal arteritis) may cause episodes of transient vision loss and transient diplopia. It is seen in elderly patients and is more common in women and Caucasians. It is important to ask patients about systemic symptoms suggestive of giant cell arteritis, such as fevers, chills, unintentional weight loss, achy shoulders and hips, headaches, scalp tenderness, and jaw claudication. Jaw claudication is ischemic pain that develops when using the jaw muscles (typically when chewing) and improves with rest because the arteries affected by arteritis are not able to respond to the increased perfusion requirements when the muscles are in use. Fundus examination may show additional signs of ischemia, such as cotton wool spots. Fluorescein angiogram may show choroidal hypoperfusion. As patients with transient vision loss due to giant cell arteritis are likely to have permanent vision loss due to ischemia within hours to days, it is essential to have a low threshold to evaluate for this diagnosis. It is a good rule of thumb to send inflammatory markers (ESR, CRP, and platelet count) in all patients aged 50 and older who report transient monocular vision loss episodes, even if they do not report additional systemic symptoms.
Ocular hypoperfusion. Severe carotid stenosis may also cause transient monocular vision loss due to hypoperfusion. When there is borderline ocular perfusion, exposure of the retina to intense light, which increases metabolic activity in the retina, may exceed the capacity of the compromised carotid-ophthalmic artery system, leading to transient vision loss due to ocular hypoperfusion. This is often progressive vision loss, with a duration of up to 5 to 10 minutes, and may be precipitated by maneuvers that lower the perfusion pressure, such as standing up, or by maneuvers that increase the metabolic demand on the retina, such as looking at a bright light (“light-induced amaurosis”) (59).
Chronic ocular hypoperfusion may result in ocular ischemic syndrome, damaging the structures of the eye and causing severe eye pain. Examination findings include narrowed retinal arteries; dilated retinal veins; midperipheral retinal hemorrhages; cotton wool spots; microaneurysms; corneal edema; and neovascularization of the iris, optic disc, or retina.
Venous congestion. Venous congestion, such as that due to an impending central retinal vein occlusion, may cause progressive loss of vision that is often described as blurry or incomplete loss of vision with a duration of 10 to 20 minutes. In these cases, tortuosity or dilation of the retinal veins is likely to be seen; dot-blot hemorrhages may also be seen.
Central retinal artery vasospasm. Central retinal artery vasospasm is a potential cause of stereotyped, recurrent episodes of painless transient monocular vision loss that typically last 30 to 60 seconds (a few minutes at the longest), with a complete return to baseline afterward, and may be seen in young patients without vascular risk factors. Some patients report triggers, such as emotional stress, cold, or exercising (58; 35). Drugs, such as phencyclidine and cocaine, may also trigger episodes (60). In practice, this is a diagnosis of exclusion as it is unlikely that the fundus will be observed during an episode. However, cases have been reported in which the fundus was observed and photographed or videotaped during an episode, showing transient narrowing of the retinal arteries (11; 49; 32; 45). Permanent vision loss is not typically expected to occur.
Gaze-evoked amaurosis. An orbital mass may intermittently compress structures within the orbit, such as the optic nerve itself or the vascular structures, depending on gaze position (10; 44; 37; 47). Abnormal measurements on Hertel exophthalmometry are suggestive, and orbital imaging is required to evaluate for a mass.
Angle closure glaucoma. Patients may report transient episodes of blurry vision and haloes around lights and will typically have severe eye pain and headache during episodes. Examination during an episode may show a red eye with a mid-dilated pupil and elevated intraocular pressure. Episodes may be triggered by activities that cause pupillary dilation, such as watching television in a dark room. At other times, examination may look normal other than a narrow anterior chamber angle, which is best seen via gonioscopy.
Transient smartphone blindness or “smartphone amaurosis.” Transient smartphone blindness describes transient monocular loss of vision occurring immediately after using a smartphone while lying down on one side in a dark or dimly lit environment. This is a benign, physiological phenomenon caused by unequal light adaptation 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 retain dark adaptation, whereas the other eye is exposed to the smartphone’s luminance and becomes light adapted. After setting the smartphone aside, there may be transient monocular vision loss lasting for several minutes in the light-adapted eye.
Alim-Marvasti and colleagues reported recurrent transient monocular vision loss consistent with transient smartphone blindness in two 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, all of which were negative (01). Two 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. Since then, multiple similar cases have been reported (33; 54).
Transient monocular vision loss only on awakening. Bouffard and colleagues reported on 29 patients with transient monocular vision loss only present on awakening that resolved within 15 minutes, all of whom had negative extensive evaluations (09). This phenomenon can be suspected if a patient only reports transient monocular vision loss on awakening and never in other settings. The authors propose that although this phenomenon may be due to unequal light adaptation (equivalent to smartphone blindness), it may represent a separate phenomenon, such as a neurovascular autoregulatory failure resulting in a supply and demand mismatch during low-light conditions. Fortunately, whatever the mechanism, this appears to be a benign phenomenon.
Additional ocular causes. Vitreomacular traction (traction on the macular by the vitreous) may rarely cause transient vision loss. Rarely, hyphemia and other postsurgical complications may cause transient monocular vision loss.
Uncommon causes of transient monocular vision loss. Hyphemia after intraocular surgery can cause temporary visual loss (34; 02). Transient visual loss has been reported after sub-Tenon anesthesia given for cataract surgery (Feibel and Guyton 2003) and in patients with leaking blebs following trabeculectomy for glaucoma (23). Neurologists should remain aware that ophthalmic history and a complete ophthalmic examination are important parts of the evaluation of a patient with transient monocular vision loss.
Familial hemiplegic migraine with an SCN1A mutation occurred with a highly stereotyped form of transient monocular vision loss in several members of two families (61). 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 and is presumably from transient hypotension and ischemia. Vision loss can occur in both eyes after rubbing just one eye, with a 1- to 2-second delay before onset in the second eye (39). During an episode, the pupil is dilated and unresponsive to light. The episodes typically occur multiple times daily for decades without resulting in permanent vision loss (61).
There are several causes of transient monocular vision loss that patients may notice occurring in both eyes simultaneously. These are monocular phenomena involving the anterior visual pathways and, thus, often occur in one eye but can also, not uncommonly, occur in both eyes at the same time.
Transient visual obscurations. Transient visual obscurations are very brief, 5- to 15-second black or gray outs of vision that are usually precipitated by positional changes, such as bending over, or Valsalva. They occur due to high tissue pressure at the optic nerve head, usually due to optic disc edema but also occasionally due to optic nerve head drusen or anomalous optic discs.
These are most classically associated with papilledema, which is often symmetric, but in cases of unilateral optic edema or unilateral optic disc pathology, unilateral transient visual obscurations may be seen.
Uhthoff phenomena. Uhthoff phenomena may cause transient vision loss. This can be suspected in a patient with a history of demyelinating optic neuritis who notices transient recurrent visual blurring when hot, such as after a shower. Visual worsening due to Uhthoff phenomena will be less severe than the vision loss that occurred during the initial demyelinating episode.
Pigmentary dispersion syndrome. Pigmentary dispersion syndrome is due to excessive release of pigment from the iris, which can accumulate in the trabecular meshwork and reduce aqueous humor outflow. Patients may report transient episodes of blurry vision and haloes around lights. Physical exercise may be a trigger for the episodes. Patients with pigmentary dispersion syndrome may have iris transillumination defects, pigment on the corneal endothelium, pigment in the anterior chamber, and heavy pigmentation of the trabecular meshwork, also best seen via gonioscopy.
Dry eye or ocular surface. Patients with dry eye may report transient episodes of visual loss, but further questioning will reveal that this is visual blurring rather than dimness or darkness. They may also notice intermittent monocular diplopia. Symptoms are typically worse later in the day and worse with activities that decrease blink rate, such as driving, reading, and screen time. Slit lamp examination using fluorescein stain may show superficial punctate epithelial erosions and decreased tear break up time.
Migraine visual aura. Migraine visual aura is believed to be the most common cause of transient binocular vision loss.
Patients with transient vision loss due to migraine classically describe stereotyped visual disturbance events involving both eyes, which are often noted to include positive visual phenomena. The positive visual phenomena are usually described as moving and may be described as sparkles, lights, shimmering, flickering, rotating, oscillating, or a kaleidoscope phenomenon. The visual disturbance starts in one area of vision and spreads or “marches” to involve a larger area of the visual field. “Fortification spectra” is a term used to describe the characteristic phenomena and is based on an early migraineur who described his aura as consisting of lines that looked like a fortified town with bastions. As the leading edge of positive visual phenomena spreads, vision loss (scotoma) will often be noted behind it. Episodes typically evolve over the course of 15 to 30 minutes and should not last longer than 60 minutes. The visual aura may be followed by a headache with migrainous features, but this varies, and the presence of headache is not required for the diagnosis (27).
Examination may show a homonymous visual field defect during an episode, but interictal examination should be normal (22).
Migraine visual aura is a benign cause of transient visual disturbance. Red flags that should raise concern for an alternative etiology include sudden onset without build up; static location of the visual disturbance without migration; atypical time course, including very brief (such as lasting seconds) or prolonged (such as lasting more than an hour) duration; persistent unilateral location; and abnormal interictal examination.
The patient’s report of the transient visual episode as monocular should not rule out migraine as the cause for episodes that otherwise fit the description of migraine visual aura, including, most importantly, the evolution of symptoms (with gradual onset and gradual resolution), typical time course, and presence of positive symptoms, with normal baseline between episodes. Patients do not always recognize the visual disturbance to be binocular. Patients are more likely to notice the visual phenomena in the eye with the temporal field affected, possibly because the temporal field is larger than the nasal field. Patients also may not have covered one eye or the other during an episode.
Occipital transient ischemic attack. Patients who have a transient occlusion of the basilar or posterior cerebral arteries may have a transient episode of homonymous hemianopia. This should be suspected when a patient reports the sudden onset of vision loss respecting the vertical, particularly if they can confirm the vision loss was present in both eyes during the episode. Associated neurologic symptoms that localize to the posterior circulation, such as vertigo, dizziness, diplopia, ataxia, and focal weakness, are also highly suggestive of a posterior circulation transient ischemic attack. Positive visual phenomena should not be seen. The duration of the episodes should be minutes. Some patients may report an associated headache.
Seizures. Seizures occurring in the posterior parietal, posterior temporal, and occipital lobes can give rise to temporary visual symptoms and transient hemianopia. Brief, simple positive visual phenomena lasting seconds to minutes, such as flashes, are typical and may be followed by a transient hemianopia (postictal cortical blindness). Patients may have other seizures or other symptoms concerning for seizure, such as loss of consciousness or lost time. Structural lesions, such as 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 four patients had visual aura described as blurry vision, whereas 14 had “elementary visual hallucinations,” and four had “visual illusions” (68). None described transient visual blackouts.
As a transient visual loss event, by definition, resolves spontaneously, discussion of the prognosis refers to the likelihood of subsequently developing permanent vision loss or related complications. The provider’s first obligation is to identify patients who may have had transient vision loss due to a serious underlying cause that could cause permanent vision loss and serious neurologic complications if not treated quickly, particularly ischemic causes, arteritic causes (giant cell arteritis), seizures, and transient visual obscurations.
Transient intraocular pressure elevations and vitreomacular traction episodes could potentially lead to permanent vision loss, if not treated. Other causes, such as migraine visual aura, transient smartphone blindness, transient monocular vision loss on awakening, central retinal artery vasospasm, dry eye, and Uhthoff phenomena, are benign, meaning that they are not expected to cause permanent vision loss or other complications.
Patients who have episodes of transient monocular vision loss from an ischemic cause have a serious risk of subsequent permanent vision loss or cerebral stroke. A prospective study of patients presenting with ischemic causes of vision loss that included 440 eyes with central retinal artery occlusion and branch retinal artery occlusion, 1202 eyes with central retinal vein occlusion and branch retinal vein occlusion, 39 eyes with ocular ischemic syndrome, 946 eyes with nonarteritic anterior ischemic optic neuropathy, and 147 eyes with vision loss due to giant cell arteritis showed that transient monocular vision loss episodes preceded the onset of permanent vision loss in many of these patients—particularly giant cell arteritis, in which more than 30% of patients had noted transient monocular vision loss prior to the onset of permanent vision loss (26).
Another prospective study of 341 consecutive patients found that over the 4 years after a presentation for transient monocular vision loss, 4.4% per year had vascular death, stroke, myocardial infarction, or retinal infarction (62).
A prospective study of 198 patients with transient monocular blindness found that the risk of ipsilateral stroke within 3 years ranged from 2% to 24%, depending on the number of additional risk factors (05). Patients with multiple risk factors who underwent carotid endarterectomy had a decreased risk.
A prospective study capturing 826 patients with transient visual symptoms found that a major embolic source was identified in around 20%, and patients with a homonymous hemianopia were more likely to have atrial fibrillation (38). Another retrospective review that included 400 patients with monocular ischemia, including 263 patients with transient monocular vision loss due to ischemia, showed that 9% had atrial fibrillation, but this was likely an underestimate as only 53% underwent prolonged cardiac monitoring; 14% had ipsilateral carotid stenosis (69).
A study of 439 consecutive untreated patients with transient or permanent retinal artery occlusions from 1973 to 2000 showed that approximately more than 65% had ipsilateral carotid artery plaques, 30% had more than 50% ipsilateral carotid artery stenosis, and more than 50% had an abnormal echocardiogram (25). The authors emphasized that patients may have both carotid artery and cardiac disease and that patients should be evaluated for both. A prospective study of 654 patients with an episode of transient or permanent monocular vision loss found that more than 6% had a stroke within the next 5 years and more than 4% had a stroke in the carotid territory ipsilateral to the symptomatic eye, with a higher risk in patients with carotid stenosis (15). These were typically large vessel strokes.
Of note, these studies were done in an era of secondary stroke prevention treatment. The risks are likely to be higher in patients who do not undergo stroke work-up and receive secondary stroke prevention as the older literature—preceding advances in urgent stroke evaluation and treatment—showed higher rates of major stroke after an initial presentation for stroke or transient ischemic attack (06).
A week prior to presentation, a 75-year-old man had an episode of a black shade that had descended over his right eye. He had a past medical history of coronary artery disease status post coronary artery bypass surgery, hypertension, and claudication of the right leg when he walked. After about 30 seconds, he noticed the shade lifting from the bottom up. Two days prior, he had noted an episode of transient clumsiness and weakness of his left hand that resolved after 3 minutes. He had also noticed 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 otherwise normal.
Duplex sonography showed a severe stenosis of his right internal carotid artery, a finding corroborated by CT angiography of the neck. MRI showed no brain infarction. He had an uneventful right carotid endarterectomy.
The differential diagnosis of transient vision loss is broad and includes vascular, ophthalmic, and other causes—each with a different pathogenesis. The most relevant etiologies are ischemic etiologies and migraine.
Transient ischemia. Transient ischemia of the anterior circulation may cause transient monocular vision loss, whereas transient ischemia of the posterior circulation may cause transient binocular vision loss.
Transient monocular vision loss can occur due to ischemia of the anterior circulation. The internal carotid artery’s first major branch is the ophthalmic artery, which gives off the central retinal artery that supplies the retina and the posterior ciliary arteries that supply the optic nerve head. Transient ischemia can occur due to embolism, which is often due to carotid disease, or to hypoperfusion, which can occur due to severe carotid stenosis. Although stenosis of the internal carotid artery in the neck is commonly discussed, common carotid artery disease (30) and disease of the intracranial internal carotid artery (31) can also cause transient visual loss. Transient monocular vision loss due to stenosis of the ophthalmic artery has been reported as well (46). Patients with transient vision loss have a risk of subsequent ischemic stroke, but the risk is not as high as in patients who have had a cerebral transient ischemic attack. In a retrospective review of 28 patients with retinal vision loss and 26 patients with transient ischemic attack or middle cerebral artery stroke who had undergone cerebral angiogram, Rossin and colleagues found that patients who had experienced a retinal ischemic event had a more proximal angular origin of the ophthalmic artery than patients who had experienced a cerebral transient ischemic attack or stroke (53).
Episodes of transient monocular vision loss due to hypoperfusion may be seen in patients with less than 1 mm residual lumen (90% stenosis). The attacks may be brought on by standing up quickly, changes in neck position (eg, during archery or violin playing), or after eating (40). When the internal carotid artery is completely occluded, patients may show periodic dimming of vision when exposed to bright light. Patients with bilateral internal carotid occlusive disease may have had bilateral dimming of vision on bright light exposure (36).
Carotid artery dissection may also cause transient monocular vision loss. This may occur when the artery becomes acutely narrowed or occluded and may be associated with other focal neurologic symptoms due to transient ipsilateral hemispheric ischemia.
Embolism from the heart may also cause transient monocular vision loss (12; 43; 25; 69). This is a less common cause than carotid stenosis (03; 69) but may be underestimated as not all patients undergo long-term cardiac monitoring after a transient monocular vision loss event (69).
Embolism from the aorta is another potential cause, particularly during and after cardiac surgery or angiography.
Transient binocular vision loss can occur due to ischemia of the posterior circulation. Severe stenosis or occlusion or, less often, dolichoectatic dilatation of the intracranial vertebral or basilar arteries can cause an intermittent decrease in blood flow to the occipital lobes. 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 (13; 67; 38).
Pathophysiology of migraine visual aura. Migraine visual aura is thought to be due to cortical spreading depression within the occipital cortex, and the classic semiology of positive visual phenomena with fortification spectra is thought to correspond to the anatomy of the occipital cortex (52; 08; 57; 29; 55; 24). Of note, terms such as “retinal migraine,” “ocular migraine,” and “ophthalmic migraine” are sometimes used to describe migraine visual aura, particularly if it is reported to have been perceived monocularly. They are also sometimes used to describe brief (minutes) episodes of transient vision loss with negative symptoms only, consistent with central retinal artery vasospasm. When used to describe a classic migraine visual aura with features such as fortification spectra, these terms incorrectly imply a retinal or ocular localization rather that the true localization in the occipital cortex.
Stereotyped, recurrent episodes of transient monocular vision loss with no positive visual phenomena, lasting minutes, are more likely to represent central retinal artery vasospasm than migraine (29; 45; 51; 14). Although the term “retinal migraine” is included in the ICHD-3 (27), it is very difficult to meet the diagnostic criteria, and some commentators have argued that the term is a misnomer—an outdated term for central retinal artery vasospasm based on the historical theory of migraine as a vasospastic process (64; 14).
The epidemiology varies based on the underlying cause of transient vision loss.
Prevention depends on the etiology and mechanism.
Underlying disorders of both monocular and cerebral visual loss depend on the etiology and mechanism. Most relevant are vascular risk factors, as they increase the risk of ischemic causes of transient vision loss, and personal or family history of migraine, as they increase the risk of migraine visual aura.
Distinguishing whether the transient vision loss event was monocular or binocular is the first step toward localization, and taking a detailed history of the event is a key part of diagnosis (Table 2). Next, evaluation requires a thorough ophthalmic examination, including ocular surface examination; evaluation of the depth of the anterior chamber; evaluation for the presence of pigment; and evaluation for optic disc swelling, optic disc drusen, retinal emboli, and cotton wool spots as well as any focal neurologic signs.
Patients who are over 50 years old should be screened for giant cell arteritis/temporal arteritis with sedimentation rate, C-reactive protein, and platelet count.
Vessel imaging is essential, particularly carotid imaging if monocular and imaging that includes the posterior circulation if binocular. Neuroimaging to evaluate for silent strokes can be important if ischemia is suspected. Dedicated orbital imaging can be useful to rule out orbital mass.
If an ischemic cause is suspected, a full stroke work-up is needed (41). Additional work-up depends on the suspected cause of the transient vision loss episode. For example, EEG is indicated if seizures are suspected.
Treatment is dictated by the cause of the transient visual loss. Some of the causes, such as angle closure glaucoma and orbital masses, are treated by ophthalmology. The following causes are frequently treated by neurologists.
Ischemic causes. A stroke work-up should be done to assess risk factors in patients who have a vascular cause of transient monocular or binocular vision loss (41). Secondary stroke prevention treatments should be initiated. Patients with atrial fibrillation should typically be treated with anticoagulation. Patients with transient monocular vision loss who have internal carotid artery stenosis should be treated appropriately, such as with carotid endarterectomy or angioplasty with stenting, if indicated.
Arteritic causes. If there is any suspicion of giant cell arteritis/temporal arteritis, the patient should immediately be treated with high-dose corticosteroids to prevent permanent loss of vision due to ischemic events. Once the diagnosis is confirmed by a positive temporal artery biopsy, the patient should be treated with high-dose steroids or steroid-sparing agents, typically over the course of at least one year. A rheumatologist can help manage the steroid course or use of steroid-sparing agents.
Seizures. Seizures must be treated with antiseizure drugs.
Migraine visual aura. Reassurance that the episodes are benign and will not lead to permanent vision loss is very helpful for patients with migraine visual aura. Some patients are not bothered by infrequent episodes once reassured of their benign nature. If the episodes are bothersome, start with headache hygiene (hydration, sleep, avoidance of triggers, etc.). Pharmacologic migraine prophylaxis can also be helpful for reducing the frequency of episodes. Migraine abortives are not helpful for the treatment of migraine visual aura as the onset will not be quick enough to prevent the aura. However, taking a migraine abortive at the time the visual aura is noticed may be very helpful for preventing headache in patients who typically have a severe headache following the migraine visual aura.
Central retinal artery vasospasm. Reassurance that the episodes are benign and will not lead to permanent vision loss is helpful. If the patient is bothered by frequent episodes, calcium channel blockers may decrease the frequency (66; 65; 50).
Papilledema. After a work-up to evaluate for the underlying cause of papilledema, medications such as acetazolamide, topiramate, and furosemide may be used to lower intracranial pressure. Surgical management, such as ventriculoperitoneal shunt, optic nerve sheath fenestration, or transverse sinus stenting, may be indicated in severe, vision-threatening cases.
All contributors' financial relationships have been reviewed and mitigated to ensure that this and every other article is free from commercial bias.
Leanne Stunkel MD
Dr. Stunkel of Washington University in St. Louis has no relevant financial relationships to disclose.See Profile
Heather E Moss MD PhD
Dr. Moss of Stanford University has no relevant financial relationships to disclose.See Profile
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