Establishing the Diagnosis
A 6-year-old girl presents to the ophthalmologist after reporting to her parents that her vision was “black” the previous day, but has resolved, and now she reports that she is seeing normally. A complete ophthalmological exam is normal.
How should the ophthalmologist approach this child? How much of a work-up is warranted in a pediatric patient with a normal eye exam and an inexact history? It is most helpful to get as accurate a description of the visual changes from the child as possible. Ask the child to draw the visual images, or show examples of various visual phenomena to the child to see if she can relate her symptoms to these examples. Ask the parents to describe the child’s behavior during the episode. Was the child acting normally when she happened to mention a visual symptom, or was the child visibly disabled? Timing is also important, although this can be challenging to accurately assess in the young patient. It is often helpful to ask the parents how long the child was complaining or behaving differently when experiencing visual symptoms or visual loss. Exact times may not be defined, but it is useful to determine whether the symptoms lasted seconds, minutes, or hours. The frequency of the attacks can give other clues. Is this constant or episodic? Is this the first event, or is this a repeated phenomenon over months or years?1
Children, particularly bright, inquisitive, and highly observant ones, may present to the ophthalmologist with visual complaints not readily explained by objective examination. Unlike their parents, these children often are not distressed about the phenomena. The vast majority of these symptoms reflect benign entities, but could also signal migraine or a more ominous psychiatric disease or intracranial pathology. It is useful, when approaching the pediatric patient with a history of visual changes, to have an understanding of natural, entopic phenomena. The precocious child will often recognize these visual phenomena and describe what he or she sees to one or both parents. With a good understanding of normal, physiologic phenomena, the parents can be reassured that no pathologic process is involved in the visual changes the child is describing.2
Entoptic phenomena
Entoptic images result from structures “coming from within,” casting shadows onto the retina. These include vitreous floaters, the Purkinje tree (the vascular tree of the retina cast onto the photoreceptors), and the blue field entoptic phenomenon also known as Scheerer’s phenomenon. This latter entity is best seen when looking at the bright blue sky. It is the appearance of dots with “tails” resembling worms (nicknamed blue-sky sprites): They last a second or less and travel a short distance in a curvy path. They represent white blood cells moving within the capillary, followed by red cells. White blood cells do not absorb blue light, whereas red cells do; therefore, the white cells create the head of the squiggle while the red cells pile up behind it. Because of the foveal avascular zone, blue-sky sprites do not appear in the central visual field.
Mechanical pressure on the eye, such as eye rubbing, can cause fleeting sparkles of light, and also represents a form of entoptic phenomenon. These are sometimes referred to as phosphenes, defined as seeing light without light actually entering the eye. Rubbing the eye stimulates the retinal photoreceptors, causing an electrical discharge. The patient may sometimes remark upon a purple hue to the light.
Some authorities classify photopsias as larger and longer-lasting flashes of light than phosphenes. Photopsias are generated in other parts of the visual system outside the globe itself. However, most of the literature uses the two terms interchangeably. Photopsias are most commonly associated with vitreous detachment, retinal detachment, migraine with aura, migraine aura without headache, and occipital lobe disease.
Migraine aura
The most common cause of photopsias or visual disturbance in the child is migraine.3 Fifteen to 30% of children with migraine report visual symptoms. Five percent of these children only experience the aura without headache.4 As in adults, the visual symptoms are episodic visual hallucinations (not based on environmental images) that are typically unformed as colored or colorless flashes, and geometric patterns or lines. However, sometimes the hallucinations may be formed images of people, objects, or animals. In children, unlike in adults, the headache is often absent and the migraine manifests as night terrors, benign paroxysmal vertigo, cyclical vomiting, abdominal migraine, or motion sickness.
Some children may be able to describe the classical scintillating fortification scotoma that gradually expands or builds and lasts 5-30 minutes. Common descriptions of the migraine aura in children include “heat waves,” “water coming down a window,” “lines coming down the sky like it’s raining,” “sparkles,” “dancing lights,” or a “star breaking into a million pieces.” These phenomena start small then gradually enlarge to involve the entire visual field, and these visual symptoms reflect positive scotoma.5
Other children describe blurring of vision, “holes in their vision,” or kaleidoscopic vision. Migrainous visual loss can present in a variety of ways. Amaurosis fugax, or rapid onset and resolving monocular visual loss lasting minutes, is much more likely to occur in migraineurs who are children and young adults. It is rarely from embolic carotid disease, unlike in the middle-aged to older adult population. Migraineurs have also been reported to have episodes of retinal vasospasm that may represent migraine equivalents.3
Of note, some patients report changes in size of objects, or metamorphopsia of images. Images may move forwards or backwards, or only parts of the body or scene become distorted. This has been referred to as the Alice in Wonderland phenomenon.6
Visual snow
Some children may complain of constant, never-ending “TV static” that may or may not follow a stereotypical migraine event. The general public refers to this entity as “visual snow,” and it is currently classified in the International Headache Classification (IHC) as persistent migraine aura without infarction. The difficulty is in finding consistency in the medical literature because, prior to the IHC, it had been given many names including prolonged migraine aura status (first coined by Haas et al), persistent positive visual phenomenon, and migraine aura status.7
Persistent aura without infarction has been defined as aura symptoms over one week, without associated infarction. It is bilateral, lasts months to a lifetime, and most patients give a history of prior migraine or a variation thereof. They generally complain of snow or television-like-static affecting part of or the entire visual field most prominent against dark backgrounds. The visual symptoms range from “a million dots,” to “cracks and lines,” “blobs of white and gray,” comets, and grainy vision.8,9
Evaluation of these patients by neuro-imaging, electroretinogram, and electroencephalogram beyond the ophthalmological examination has proven to be inconsistent and generally yields little. Although persistent aura without infarction is classified as a form of migraine, traditional migraine medication has not been of benefit in treating it, except as indicated in anecdotal reports of single cases responsive to acetazolamide, valproic acid, lamotrigine, topiramate, and furosemide.
Synesthesia
Synesthesia is a condition in which stimulation of one sensory modality causes an experience in another sensory modality. Auditory-visual synesthesia is the term used for visual images, including photopsias in response to sound, usually unexpected and startling. For example, the most common form of auditory-visual synesthesia is when numbers, letters, or symbols generate a color. For example, number 7 may generate the color blue. Functional MRI has shown abnormal stimulation. Although these phenomena are traditionally associated with visual loss or intracranial pathology, they can also occur in the face of a normal ophthalmologic and neurologic examination.10
Occipital lobe epilepsy
There is some difficulty in distinguishing migraine visual aura from the epileptic photopsias of a seizure disorder. Occipital lobe epilepsy is most common in the pediatric group. Visual aura of migraine typically develops over minutes and there is mix of positive and negative scotomata. These scotomata typically start small, enlarge, scintillate, and migrate. The scotomata are often linear, with jagged edges. Headache or other signs and symptoms are often present, as noted with pediatric migraines.
The visual symptoms of occipital pole (area 17) epilepsy are also typically simple, elementary, unformed hallucinations. But they lack form and depth and generally do not create a fortification scotoma. They may be colored or colorless and are circular or spherical. Seizures in the visual association areas (areas 18 and 19) tend to have more elaborate form, color, depth, and movement. Photopsias of seizures last only seconds or, rarely, minutes before onset of a seizure. Twenty-nine percent of patients with occipital lobe epilepsy experience blackout of vision.11 These visual symptoms may be followed by minimal alterations in consciousness, therefore not raising suspicion for seizure disorder, or may be associated with dramatic seizure manifestations with generalization. It is important to recognize that postictal headache is a common complaint, making differentiation from migraine sometimes difficult. Finally, occipital lobe seizures tend to occur daily, whereas migraine-associated visual hallucinations occur with longer intervals between attacks.
It is particularly important to differentiate between epilepsy and migraine in the child who harbors a tumor or arteriovenous malformation (AVM) in the occipital lobe. A lesion in the occipital lobe can irritate the surrounding brain matter, leading to seizure activity. Of note, the elementary, unformed hallucinations associated with a seizure focus tend to start more abruptly and remain stationary, contrasting with the building, growing fortification scotoma of migraine. In addition, the visual disturbances of an AVM will usually stay on the same side of the visual field (opposite the lesion).3
Some children with occipital lobe epilepsy may experience ictal cortical blindness, in which the major manifestation of the seizure is blindness. If the seizure remains isolated to the occipital lobe, the patient may not demonstrate other symptoms of seizure, and simply have episodes of complete blindness. Due to the short nature of the attacks, it may be difficult to obtain an EEG during an episode, so the diagnosis would come from history and interictal epileptiform activity.3 After a seizure, children may also develop visual loss or postictal blindness. This is typically a transient phenomenon, lasting hours to days; however, permanent visual loss after a seizure has been reported.
Transient visual obscurations
There are other causes of transient visual loss in children. Orthostatic hypotension can cause brief episodes of bilateral vision loss or blurring if the child stands too quickly. Visual loss lasting seconds, also known as transient obscurations of vision (TOV), is characteristic for papilledema and uncommon in patients with optic disc drusen. Patients with optic disc edema may complain of “grayouts” or “blackouts” of vision associated with changes in position. TOVs are probably explained by increased interstitial pressure, which causes a small decrease in perfusion pressure (such as is caused by positional changes) to cause hypoperfusion of the optic nerve. TOVs have been reported in optic disc drusen, peripapillary staphyloma, and other congenital anomalies of the optic nerve head. Contractile elements surrounding the optic nerve head are implicated as the mechanism.1
Psychogenic visual loss
Finally, a major difficulty in the diagnosis of transient visual loss in children is that a large proportion of children claiming visual loss suffer from nonorganic, or psychogenic, visual loss. This should be a diagnosis of exclusion, and the onus is on the ophthalmologist to rule out organic causes of visual loss. Psychogenic visual loss is most common in prepubescent girls ages 9-11, and was termed the "amblyopic schoolgirl syndrome" by Mantyjärvi.12 There are different theories as to why this occurs, many relating to stress at school or at home. Regardless, proving the nonorganic nature of the problem is sometimes difficult. Close follow-up is warranted; many conditions such as craniopharyngioma, Stargardt macular dystrophy, or X-linked adrenoleukodystrophy are initially diagnosed with nonorganic visual loss if there is no obvious optic nerve pallor or and there are no neuro-ophthalmic signs early in the disease.3
References
- Ahmed R, Foroozan R. Transient monocular visual loss. Neurol Clin. 2010; 28:619-629.
- Wright JD, Boger WP III. Visual complaints from healthy children. Surv Ophthalmol. 1999; 44:113-121.
- Brodsky MC. Transient, unexplained, and psychogenic visual loss in children. Pediatric Neuro-ophthalmology, 2nd New York: Springer. 213-252.
- Shevell MI. Acephalgic migraines in childhood. Pediatr Neurol 1996;14:211-215.
- Dooley JM, Pearlman EM. The clinical spectrum of migraine in children. Pediatr Ann 2010; 39:108-415.
- Lippman CW. Hallucinations of physical duality in migraine. J Nerv Ment Dis 1953;117:345-350.
- Headache Classification Subcommittee of the International Headache Society. The International Classification of Headache Disorders, 2nd Cephalalgia. 2004; 24 (Suppl 1) 9-160.
- Liu GT, Schatz NJ, Galetta SL, Volpe NJ, Skobieranda F, Kosmorsky GS. Persistent positive visual phenomena in migraine. Neurology. 1995; 45:664-668.
- Liu GT, Volpe NJ, Galetta SL. Visual hallucinations and illusions. In: Neuro-ophthalmology: Diagnosis and Management, 2nd New York: Saunders Elsevier. 393-414.
- Celesia GG. The mystery of photopsias, visual hallucinations, and distortions. Suppl Clin Neurophy 2006;59:97-103.
- Salanova V, Andermann F, Olivier A, Rasmussen T, Quesney LF. Occipital lobe epilepsy; electroclinical manifestations, electrocorticography, cortical stimulation and outcome in 42 patients treated between 1930 and 1991. Brain. 1992; 115:1655-1680.
- Mantyjärvi MI. The amblyopic schoolgirl syndrome. J Pediatr Ophthalmol Strabismus. 1981;18:30-33.