Introduction

Neurologic disorders affecting the eye and the visual pathways are an important potential cause for decreased vision and morbidity in the pediatric population. Identification of these disorders is important in order to prevent vision loss but also to identify other potentially lethal abnormalities of the nervous system.

Cortical visual impairment

DEFINITION/OVERVIEW AND ETIOLOGY

Cortical visual impairment (CVI) implies visual abnormalities secondary to damage to the posterior visual pathways, and mainly to the lateral geniculate body, the optic radiations, and the occipital cortex. The term ‘cortical blindness’ is old terminology which is no longer in favor. Blindness implies that the patient has no vision and no ability to recover. Both of those implications are incorrect. Cerebral visual impairment is synonymous with CVI and is preferred by some authors.

The most common cause of CVI is hypoxic ischemic injury. This is particularly the case in preterm infants. Their immature vascular system is prone to pressure fluctuations with resultant wound ischemia to the watershed area lying in the periventricular region. Within the periventricular area are the optic radiations. Also residing in this area is the germinal matrix, the area of the brain where all neurons originate. It is a very metabolically active area in the ventricular wall. The vasculature is friable and prone to hypoxic ischemic injury, leading to hemorrhage, termed germinal matrix hemorrhage. This hemorrhage can break through from the periventricular white matter into the ventricle leading to intraventricular hemorrhage, and possible subsequent hydrocephalus.

CLINICAL PRESENTATION

Patients with CVI display a wide range of visual disability ranging from no light perception to normal visual acuity but with visual field deficits. Cognitive visual disability is also considered a form of cortical impairment and includes difficulties navigating and route finding,

difficulty finding objects in crowded scenes (making reading difficult), and difficulty recognizing people’s faces.1

Other causes of CVI include hypoxia and ischemia unrelated to preterm delivery. Asphyxia and ischemia can occur in term infants. Congenital cerebral malformations, head trauma, metabolic and neurodegenerative disorders, meningitis and encephalitis, and hydrocephalus can all cause CVI.

DIAGNOSIS AND DIFFERENTIAL DIAGNOSIS

Diagnosis is made using the patient’s history of brain injury and lack of visual attentiveness. Most patients have neurologic deficits that correspond to their vision loss. Vision loss very rarely occurs in isolation from any other neurologic problems or brain damage.2 Examination reveals variable degrees of decreased vision or visual attentiveness, no nystagmus, normal pupillary reactivity, and a normal retina and optic nerve examination. Because the damage to the visual pathways is behind the lateral geniculate body, there will be no optic atrophy in most cases. Therefore, a normal eye exam with very poor vision is a classic presentation for CVI. Magnetic resonance imaging (MRI) is the best means of studying the occipital cortices and may be helpful in patients with suspected CVI.

Differential diagnosis includes any anterior pathway visual disturbance causing vision loss.

MANAGEMENT/ TREATMENT

There is no treatment to improve vision. Treatment is aimed at providing low-vision services and supporting the vision available.

Migraine headache

DEFINITION/OVERVIEW AND ETIOLOGY

Migraine is not simply a headache but a constellation of abnormal neurologic events. It is often inherited and more often occurs in females than males; when children are analyzed separately, however, boys and girls under 7 years of age have an equal prevalence. Females predominate after that age. Children present differently from adults. Migraines typically begin at puberty and decrease in frequency at menopause. The median attack rate is 1.5 per month and the median duration is 24 hours, with a range of 4–72 hours, slightly less in children.

The neurologic events that lead to migraine all are poorly understood but felt to be secondary to hyperexcitable brainstem nuclei activating portions of the cortex. This increased activity leads to decreased blood flow and spreading cortical electrical depression, producing neurologic events such as visual aura. There is also dilation of the meningeal vessels with the release of inflammatory products leading to pain.

CLINICAL PRESENTATION

The migraine headache is often a throbbing hemicranial pain but can be anywhere on the head. It is also often accompanied by nausea and/or vomiting, photophobia, and phonophobia. Patients often sleep, and rest relieves the pain. Pediatric migraneurs often have a history of migraine equivalent which includes colic, recurrent abdominal pain, cyclic vomiting, or night terrors. Patients may experience irritability or lethargy. Triggering factors include menstruation, hunger, stress, chocolate and caffeine, sleep deprivation and, occasionally, visual triggers such as flickering lights or a computer screen. Approximately 4% of all pediatric headaches are migraine.

Transient visual disturbances occur more frequently in the pediatric age group, in some 18% of children with migraine. The stereotypical aura usually lasts 25–30 minutes. Since the visual aura is created by the brain, both eyes ‘see’ the image in the same hemifield. Some children can describe the classical scintillating scotoma which consists of a ‘fog’, or ‘seeing through water’, or

an area of loss of vision in one hemifield, surrounded by a colored shimmery zigzag line, which moves across the visual field. The scintillating scotoma then regresses. The clinical presentation described above is classic migraine. It can occur prior to a headache. If it occurs in the absence of a headache it is termed acephalgic migraine. If the scintillating scotoma occurs in just one eye it is a retinal event and is termed retinal migraine.

Some patients present with cranial nerve palsies such as cranial nerve 3, 4, and 6. The paresis begins at the peak of the headache and last days to weeks after the headache resolves. These are very rare.

DIAGNOSIS AND DIFFERENTIAL DIAGNOSIS

The diagnosis of migraine is based on history. There is often a family history of migraine or sick headaches. Intracranial masses can also cause headache and vomiting, particularly in the morning on awakening.

MANAGEMENT/ TREATMENT

Pharmacologic treatment for pediatric headache can be divided into abortive and prophylactic therapy. Most patients seek no treatment other than over-the-counter medications for symptomatic relief of their migraine headaches such as aspirin, acetaminophen, and ibuprofen. Medications can also include amitriptyline, propranolol, selective serotonin reuptake inhibitors, anticonvulsants, tricyclic antidepressants, calcium channel blockers, and 5-HT2 antagonists.

Nystagmus is an involuntary rhythmic movement of the eyes. The beating of the eyes in usually in the horizontal direction and is present in all positions of gaze. The etiology is unknown but it may be heritable. It is theorized that there is an ocular motor circuitry problem.

CLINICAL PRESENTATION

Patients with congenital nystagmus present with nystagmus at 2–4 months of age. At the time of onset the vision is somewhat reduced when compared to the visual attentiveness of children without nystagmus, but the vision improves quickly and the parents usually report no reduction in vision after 6 months of age. The typical eye exam reveals good vision, and normal pupils, retinas, and optic nerves.

Over time the amplitude of the nystagmus lessens and it becomes less noticeable. Head shaking may accompany the nystagmus. In time patients may develop a head turn. This forces the eyes into an extreme gaze position and quietens the nystagmus, termed a null point. Another dampening mechanism is convergence, so patients will hold near material very close for best vision. Patients do not complain of oscillation of the environment, termed oscillopsia. The ultimate visual acuity of these patients is usually better than 20/60, and can be near normal.

DIAGNOSIS AND DIFFERENTIAL DIAGNOSIS

The diagnosis is often made clinically. The eye exam reveals no retinal or optic nerve pathology. An electoretinogram to rule out any retinal dystrophy can also be considered. Neuroimaging is usually not performed unless other neurologic abnormalities are present and the nystagmus is atypical.

Care should be taken to rule out sensory causes of nystagmus such as any abnormality of the retina or optic nerve that leads to vision loss. Poor vision from congenital retinal or optic nerve disease causes an early-onset nystagmus and poor vision, unlike the normal or near normal vision in patients with congenital motor nystagmus. Common congenital retina and

MANAGEMENT/ TREATMENT

Drug therapy to dampen the nystagmus is not successful. Some advocate base-out prisms to induce convergence. Contact lenses may dampen the nystagmus. Surgery on the extraocular muscles can improve an abnormal head position that is adopted to dampen the nystagmus (null point). Surgery to improve visual function and dampen the amplitude of the nystagmus in some patients may be performed by detaching all four horizontal rectus muscles and then reattaching them at the same site.3

DEFINITION/OVERVIEW AND ETIOLOGY

Spasmus nutans is a constellation of nystagmus, head nodding, and a torticollis. It is an acquired form of nystagmus that generally appears between 1 and 3 years of age. The etiology of typical spasmus nutans is unknown. However, rarely a suprasellar tumor such as a chiasmal glioma can cause clinical findings identical to those seen in spasmus nutans.4

CLINICAL PRESENTATION

Children present with a shimmering, smallamplitude, high-frequency nystagmus that is often asymmetric between the two eyes; in some cases the condition appears to be monocular. It is usually horizontal in direction but there can be a vertical component. Vision is good. A combination of head nodding and lateral shaking is also present and may be compensatory. A head tilt or turn is a variable finding and presents in less than half the cases. The nystagmus often remits a few years after onset.5

DIAGNOSIS AND DIFFERENTIAL DIAGNOSIS

Diagnosis is based on the clinical findings. A suprasellar tumor can rarely present with spasmus nutans. Some neurodegenerative diseases have also occasionally been known to cause nystagmus typical of spamus nutans, such as Pelizaeus–Merzbacher disease and Leigh disease.

MANAGEMENT/ TREATMENT

There is no treatment for typical idiopathic spasmus nutans. Neuroimaging should be performed to rule out a suprasellar tumor.

DEFINITION/OVERVIEW AND ETIOLOGY

Opsoclonus is an acquired ocular movement abnormality that is characterized by involuntary chaotic bursts of multidirectional nystagmus. If the oscillations are purely horizontal, they are termed ocular flutter. Opsoclonus differs from nystagmus in that the oscillations are not rhythmic and are punctuated by silent periods.

The etiology of opsoclonus is secondary to neuroblastoma, due to a paraneoplastic phenomenon, and secondary to encephalitis affecting the cerebellum, and less often to exposure to toxins or drugs, meningitis, and intracranial tumors. It is felt that there is an inhibition of the pause cells of the cerebellum, allowing the burst cells to fire without interruption. In the case of neuroblastoma it has been hypothesized that a peptide produced by the tumor directly affects the cerebellum and causes the opsoclonus, or that the opsoclonus is due to an immunological cross-reactivity between the tumor and normal cerebellar neurons.

CLINICAL PRESENTATION

Patients present with a bizarre chaotic nystagmus, with the eyes moving in different directions, followed by periods of quiet. Young patients often complain of oscillopsia and have fairly good visual function in spite of the largeamplitude nystagmus. The eye exam is normal except for the movement abnormality. Patients with neuroblastoma may also exhibit myoclonus.

DIAGNOSIS AND DIFFERENTIAL DIAGNOSIS

After the diagnosis of opsoclonus is made, a work-up for neuroblastoma in the abdomen, chest or neck must be carried out with MR imaging. A toxin screen can be considered as well as neuroimaging of the brain. Because of its unique and remarkable appearance, no ocular movement abnormality can be confused with opsoclonus.