In adults, transient visual loss is a frequently encountered complaint that, in most cases, has an identifiable cause. The loss of vision may be monocular or bilateral and may last from seconds to hours. Episodes are usually ischemic in origin. Causes of ischemic transient visual loss include giant cell arteritis, cerebrovascular ischemia, retinal arteriolar emboli, and amaurosis fugax syndrome. Transient visual loss can therefore be a symptom of a serious vision or life-threatening condition, requiring urgent investigation and treatment, or it may have a more benign origin (eg, migraine).
Transient visual loss is a symptom rather than a diagnosis. It may be a manifestation of a number of different ophthalmic and systemic conditions,  including the following:
Hypoperfusion (eg, hypotension, cardiac arrhythmias, anemia, heart failure)
Increased plasma viscosity (eg, leukemia, lymphoma)
Atherosclerotic and arteritic cerebrovascular disease
Orbital apex mass or retrobulbar tumors
Epileptic seizure (occipital lobe seizures)
Transient hypoxia of any part of the visual system can result in a temporary disturbance of vision. Compromised perfusion of the occipital lobe, the visual pathways, or the eye may be secondary to thromboembolism, hypoperfusion, or angiospasm.
Embolic occlusions of the arteries supplying the eye are a common cause of transient visual loss in adults. Emboli causing circulatory disturbances may originate in the heart or the carotid arteries. Embolic events are usually isolated, so, if visual disturbance occurs frequently, it is less likely that emboli are responsible.
Hypoperfusion may be due to hypotension, cardiac arrhythmias, anemia, heart failure, or atherosclerotic and arteritic cerebrovascular disease. Arteritic and nonarteritic anterior ischemic optic neuropathy may also present with transient visual loss.
Angiospasm may cause a temporary reduction in blood flow to the visual system and transient visual disturbance.
Children with transient visual loss are less likely to have an ischemic cause for their symptoms and are more likely to have a benign disorder. In some children, a cause for the visual disturbance cannot be identified, and the symptoms remain medically unexplained. 
The etiology of transient visual loss includes the following:
Local ocular conditions
Ingestion of a large meal
Elevated intracranial pressure (ICP)
Minor head injury (occipital trauma)
Transient visual loss may be related to local ocular conditions, such as ocular surface disorders, intraocular foreign bodies, central or branch retinal vein occlusion, central or branch retinal artery occlusion, anterior ischemic optic neuropathy, intermittent angle closure glaucoma, and optic neuritis. Transient visual loss is also recognized in association with optic disc drusen and colobomas. [4, 5] The mechanism for transient visual loss in these conditions is not fully understood but may be related to hypoperfusion of the optic nerve.
Transient visual loss has been reported to occur after ingestion of a large meal.  Visual loss occurs secondary to hypoperfusion of the eye, as blood is shunted to the mesenteric system. Postprandial visual loss is most common in individuals whose ocular perfusion is already compromised (eg, carotid disease). 
Transient visual loss when exercising may be due to the Uhthoff phenomenon associated with demyelination.
Entopic phenomena are images produced by the eye’s own structures. These images may occur in the normal eye or may reflect abnormalities of ocular structure. Examples of entopic phenomena include the following:
Floaters – These may be due to posterior vitreous detachment or vitreous hemorrhage or may be from the normal vitreous
Phosphenes – These are luminous sensations that may be induced by mechanical distortion of the retina resulting from eye rubbing or saccadic eye movements 
After-images – These are persistent images that remain after the object is removed; they are normal sensation that depend on the intensity and duration of the stimulus
Transient visual obscurations are episodes of visual disturbance that last only seconds and are often associated with raised ICP.
Posttraumatic transient cortical blindness is thought to be due to transient hypoxia and cerebral dysfunction. [8, 9] In these cases, vision returns to normal within minutes to hours, with no permanent neurologic sequelae.
Occasionally, transient visual loss is familial. Multiple episodes of transient visual loss have been described in children with elicited repetitive daily blindness. This rare condition is associated with childhood epilepsy and familial hemiplegic migraine. 
Migraine is probably the most common cause of transient visual loss in children.  Migraine with aura is a common cause of transient visual disturbance at any age. In a study of 83 patients younger than 45 years with episodic visual loss, migraine was the most likely cause in the majority of cases.  In children, 3.5-5% suffer from recurrent migraine headaches; however, only 18% have migraine with aura, and only 5% have aura without headache.
Migrainous visual disturbances are also common in the elderly. Visual aura occurs in 1-2% of elderly patients, and in 58%, aura is not associated with a headache. 
Migraine auras are typically bright and shimmering with a dynamic quality, whereas ischemia tends to produce dark and static defects. These differences notwithstanding, it may be difficult to distinguish between migraine and amaurosis fugax. The International Headache Society (IHS) defines an aura as a recurrent disorder that develops over 5-29 minutes and lasts for less than 1 hour. 
Migraine with visual aura is thought to be due to dysfunction of the striate cortex arising from a reduction in cerebral blood flow from the terminal branches of the basilar artery. Visual symptoms include photopsia, teichopsia (fortification spectra), scotoma, hemianopia, and diplopia and are usually homonymous.  There may also be associated neurologic symptoms, such as paresthesia, weakness of limbs, speech disturbance, and vertigo.
Unilateral symptoms are rare but may occur in retinal or ocular migraine. Retinal migraine is presumed to be due to isolated hypoperfusion of the retina or the optic nerve.  This condition is defined as a fully reversible monocular visual disturbance associated with migraine headache and a normal neuro-ophthalmic examination between attacks. Retinal migraine is not as common as was once thought; one literature review found only 5 cases meeting the IHS criteria for diagnosis. 
Medically unexplained visual loss
Sometimes, despite investigations, the cause of the visual loss cannot be determined. Medically unexplained visual loss has been defined as an apparent afferent or efferent dysfunction that is not associated with an identifiable lesion in the visual pathway.  The diagnosis of medically unexplained visual loss depends on a normal examination, normal investigations, nonphysiologic patterns, and an observation period. Tests for suspected medically unexplained visual loss include the following  :
4-D base-out prism tests
Monocular vertical prism dissociation tests
Visual field tests
Color vision assessments
However, in transient visual loss, the use of orthoptic tests is limited by the temporary nature of the symptoms.
Patients with medically unexplained symptoms are frequent attenders. In primary care, 1 of every 5 new consultations involves a patient with symptoms for which no organic cause is found.  Despite the frequency of unexplained symptoms, there has been little research in this area.
Studies in adults suggest that childhood experiences, including illness in family members and previous medical consultations, are contributing factors to unexplained symptoms in later life. A series by Taich et al found that 26.7% of patients with medically unexplained visual loss had a previous diagnosis of depression, anxiety, or attention deficit hyperactivity disorder, and 31% had significant stress at school or at home.  Many patients have been seen by other specialties with unexplained symptoms.
A study of 58 patients with medically unexplained visual loss found that 79% were female and 21% were male.  Of these patients, 36% had been seen in other medical specialties with unexplained symptoms. Only 22% of patients showed improvement in visual function, a figure considerably lower than that cited by a previous study, in which 60% improved. 
If no medical explanation is found for visual loss in a child, parents may be anxious and keen for further investigations. A supportive approach is required, and the need for investigations must be balanced against the risks of exacerbating fears of disease.  It is important to establish a good rapport with the parents and the child with transient visual loss.
The frequency of transient visual disturbance in children is not known with certainty but is understood to be low. Worldwide, transient visual loss is uncommon.
Transient visual disturbance is more common in adults than in children. In addition, its etiologic profile in adults differs from that in children.
The overall sex distribution of transient visual loss in children is not known. However, migraine, a common cause of transient visual loss at all ages, is more common in females than in males. In the United States, the 1-year prevalence of migraine is 14-18% in females and 6% in males, although the female predominance is not seen until after menarche.  In children younger than 7 years, boys are affected by migraine approximately as often or slightly more often than girls are. 
Medically unexplained visual symptoms are more common in women than in men. According to Griffiths et al, of those affected with medically unexplained visual loss, 79% are female and 21% are male. 
Because of the many causes of transient visual disturbance, a structured approach to both the assessment and the management of these patients is essential. The likely causes of transient visual loss vary according to the age of the patient. Ischemic causes are more common in patients older than 45 years; however, cases of central retinal artery occlusion and central retinal vein occlusion have been reported in children. 
Perhaps the most important element to ascertain from the history is whether the visual disturbance is monocular or binocular. [25, 26] A monocular visual disturbance is more likely to be secondary to a circulatory disturbance of the anterior circulation (eg, carotid artery) than a binocular visual disturbance, which is often due to a disturbance of the posterior circulation (eg, vertebral or basilar artery). Unfortunately, patients, particularly children, often have difficulty distinguishing between monocular and binocular symptoms.
Transient monocular visual loss is often referred to as amaurosis fugax, irrespective of the cause. However, it is more accurate to reserve the term amaurosis fugax for episodes of transient monocular blindness resulting from ischemia.  A vertebrobasilar disturbance may cause a visual transient ischemic attack (TIA).
Amaurosis fugax and a visual TIA are similar in several respects: Both are of sudden onset, last 2-30 minutes, and resolve quickly without pain. Amaurosis fugax typically consists of a gray curtain that progresses from the periphery and moves toward the center of vision. It is vital to identify patients whose visual disturbance is ischemic because these patients are at greater risk for cerebrovascular accident, cerebral TIA, and myocardial infarction (MI).
The risk of further thromboembolic events is less after amaurosis fugax than after a visual TIA.  Repeated episodes of visual loss may be of thrombotic rather than embolic origin.
Whereas amaurosis fugax lasts only a few minutes (rarely longer), with vision returning to normal within 10-30 minutes, a migraine headache tends to last 2-3 hours (rarely more than 12 hours). The visual disturbance in migraine expands slowly over 10-20 minutes and rarely lasts more than 30 minutes.
Any precipitating factors for the visual loss should be elicited. For example, visual loss related to orthostatic changes may occur in patients with papilledema. The patient should be asked about the specific nature of the disturbance. Ischemic visual disturbances, such as amaurosis fugax, are classically associated with negative phenomena (eg, a blackout of vision or a curtain across the vision). Migraine tends to produce positive phenomena (eg, sparkling lights or zigzag lines).
Associated symptoms may provide important clues to the etiology. Adults should be specifically asked about the symptoms of giant cell arteritis. Children should be asked about headaches and specifically about features of headaches that may suggest raised intracranial pressure (ICP) or migraine.
As part of the medical history, the patient’s ischemic risk factors should be assessed, including any history of hypertension, diabetes, or high cholesterol levels. Inquire about a personal history of migraine, as well as about a family history. Consider whether the patient has any systemic conditions (eg, collagen vascular disease, sickle cell disease, or vasculitis).
The examination should look for ocular and systemic causes of the visual disturbance, as follows:
Check visual acuity; in children who are old enough to report a visual disturbance, it is possible to measure a Log Mar or Snellen visual acuity.
Check the pupils for a relative afferent pupillary defect
Examine the visual fields, perform a cover test, and examine extraocular motility
Examine the eye; transient visual disturbance may be caused by intermittent angle-closure glaucoma, corneal disease (eg, corneal ulcers, corneal abrasions), or uveitis
Perform a slit-lamp examination of the anterior segment, including fluorescein examination of the tear film, conjunctiva, and cornea, and measure the intraocular pressure (IOP); anterior-segment causes of transient visual loss are many, ranging from tear film abnormalities to intermittent angle closure 
Perform dilated funduscopy; this may reveal optic disc edema, retinal emboli, or ocular ischemia
If pain is present, look for its specific causes (eg, angle-closure glaucoma, optic neuritis, or optic disc edema, suggesting increased IOP)
The differential diagnosis includes the following:
Other problems to be considered include the following:
Ocular surface problem
Orbital apex lesion
Children with transient visual loss should undergo a basic laboratory workup. Blood pressure should be checked, in that hypotension is a not infrequent cause of visual disturbance. The following blood investigations should be considered:
Complete blood count (CBC) to check for conditions such as anemia and polycythemia
Connective tissue diseases (eg, Wegener granulomatosis)
Coagulopathy studies (eg, for antiphospholipid syndrome)
Sickle cell test
A hypercoagulable thrombotic state may exist as a consequence of increased activity of procoagulant compounds (eg, prothrombin, factor Va, thrombin, and fibrinogen), decreased levels of anticoagulants (eg, protein C, protein S, and antithrombin III), or decreased levels of fibrinolytic compounds (eg, plasminogen and plasmin).
Hypercoagulability may also be caused by antibodies against membrane phospholipids and plasma proteins (eg, lupus anticoagulant and anticardiolipin antibodies). Young people with transient focal neurologic events, particularly those with monocular visual symptoms and no family history of migraine, may have antiphospholipid antibodies. 
Urinalysis should be done to check the urine for glucose.
Although transient visual loss in children is most often benign, a serious underlying cause should be excluded. If symptoms are medically unexplained, clinical judgment should be used in deciding on appropriate circumstances for neuroimaging studies and further investigations.
Neuroimaging studies should be considered in the following:
History of recent head trauma
Focal neurological deficits
Limited eye movement
There should be a low threshold for neuroimaging studies in young children or where there are any suspicious features.
Echocardiography and Electrophysiology
Consideration should be given to echocardiography, depending on the history and systemic examination findings.
When visual loss is medically unexplained, it is important to address the possibility that a subtle pathologic condition may be present that was missed on an initial examination. Accordingly, electrophysiology should be considered to exclude abnormalities such as Batten disease or Stargardt disease.
Transient monocular visual loss in adults is usually caused by an atheromatous plaque in the carotid bifurcation that creates a temporary reduction in retinal blood flow.  Therefore, in adults with transient monocular visual loss, it is essential to evaluate the carotid circulation. In contrast, no cases of transient visual loss due to atheromatous carotid disease have been reported in children.
Treatment & Management
The treatment of transient visual loss depends on the cause.
If an ischemic event is suspected, then the patient should be referred to a physician for investigation of any cardiovascular and cerebrovascular risk factors. Some of these patients benefit from antithrombotic therapy or carotid surgery. If the transient visual loss is monocular, then the carotid system should be investigated, usually by means of carotid Doppler ultrasonography.
Other investigations may include echocardiography, a complete blood count (to rule out anemia), and inflammatory markers when giant cell arteritis is suspected. Neuroimaging is important for ruling out intracranial pathology affecting the visual pathway, particularly in patients with binocular disturbance.
In cases where the diagnosis is uncertain, adequate follow-up care is important. Children with unexplained transient visual disturbances should be closely monitored.
The prognosis of transient visual disturbance is better for children than for adults. In a study of the long-term prognosis for adolescents and young adults with transient bilateral visual loss, Bower et al followed 13 patients aged 8-38 years who had 1 or more sudden transient attacks of bilateral blindness; none of the 13 suffered a major vascular event over a mean follow-up of 10 years.  . The authors concluded that investigations are unlikely to reveal a cause for visual loss and that the prognosis for these patients appears benign.
When a patient presents with transient visual disturbance, the underlying cause must be ascertained and any serious treatable disorder excluded. In adults, identifying risk factors (eg, hypertension, hypercholesterolemia, and carotid artery disease) and treating systemic disease are important.
For example, if retinal emboli are found, the patient must be promptly referred for evaluation and management of cardiovascular risk factors. The Beaver Dam Eye Study found that participants with retinal emboli who present at baseline had a 3-fold higher risk of 8-year mortality from stroke than persons without emboli. 
Although children are more likely to have a benign cause of their symptoms, some may have a serious underlying problem. For example, cases of central retinal artery occlusion and central retinal vein occlusion in children have been reported to be associated with trauma, vasculitis, antiphospholipid antibody syndrome, sickle cell disease, and leukemia. [32, 33]