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Disorders of the Visual System


Both congenital and acquired visual impairments in children are often associated with neurological disorders. The most common visual disorders are uncorrected refractive errors, amblyopia, strabismus, cataracts, and genetic disorders.

Assessment of visual acuity

The assessment of visual acuity in preverbal children relies mainly on assessing fixation and tracking as the infant or young child interacts with the environment.

Clinical Assessment

The pupillary light reflex is a test of the functional integrity of the subcortical afferent and efferent pathways and is reliably present after 31 weeks’ gestation. A blink response to light develops at about the same time, and the lid may remain closed for as long as light is present (the dazzle reflex). The blink response to threat may not be present until 5 months of age. These responses are integrated in the brainstem and do not provide information on the cognitive (cortical) aspects of vision.

Observing fixation and following behavior is the principal means to assess visual function in newborns and infants. The human face, at a distance of approximately 30 cm, is the best target for fixation. Ninety percent of infants fixate on faces by 9 weeks of age. After obtaining fixation, the examiner slowly moves from side to side to test tracking . Visually directed grasping is present in normal children by 3 months of age but is difficult to test before 6 months of age. Absence of visually directed grasping may indicate a motor rather than a visual disturbance.

The refixation reflex evaluates the visual fields in infants and young children by moving an interesting stimulus in the peripheral field. Clues to visual impairment are structural abnormalities (e.g., microphthalmia, cloudy cornea), an absent or asymmetric pupillary response to light, dysconjugate gaze, nystagmus, and failure to fixate or track. Staring at a bright light source and oculodigital stimulation indicate severe visual impairment.

Visual Evoked Response

The visual evoked response to strobe light demonstrates the anatomical integrity of visual pathways without patient cooperation. At 30 weeks’ gestation, a positive “cortical” wave with a peak latency of 300 ms is first demonstrable. The latency linearly declines at a rate of 10 ms each week throughout the last 10 weeks of gestation. In the newborn, the morphology of the visual evoked response is variable during wakefulness and active sleep and easiest to obtain just after the child goes to sleep. By 3 months of age, the morphology and latency of the visual evoked response are mature.

Congenital blindness

Cortical blindness is the most common cause of congenital visual impairment among children referred to a neurologist. Ophthalmologists are more likely to see ocular abnormalities. The causes of congenital visual impairment are numerous and include prenatal and perinatal disturbances. Optic nerve hypoplasia, with or without other ocular malformations, is the most common ocular abnormality, followed by congenital cataracts and corneal opacities. Corneal abnormalities usually do not cause visual loss unless clouding is extensive. Such extensive clouding may develop in the mucopolysaccharidoses and in Fabry disease. Box 16.1 lists conditions with corneal clouding present during childhood.

Box 16.1
Corneal Clouding in Childhood

  • Cerebrohepatorenal syndrome (Zellweger syndrome)

  • Congenital syphilis a

    a Denotes the most common conditions and the ones with disease modifying treatments

  • Fabry disease (ceramide trihexosidosis)

  • Familial high-density lipoprotein deficiency (Tangier island disease)

  • Fetal alcohol syndrome

  • Glaucoma a

  • Infantile GM 1 gangliosidosis

  • Juvenile metachromatic dystrophy

  • Marinesco-Sjögren disease

  • Mucolipidosis

  • Mucopolysaccharidoses

  • Multiple sulfatase deficiency

  • Pelizaeus-Merzbacher disease

  • Trauma (forceps at birth)

Congenital Cataract

For the purpose of this discussion, congenital cataract includes cataracts discovered within the first 3 months. Box 16.2 lists the differential diagnosis. Approximately one-third are hereditary, one-third are syndromic, and one-third are idiopathic.

Box 16.2
Cataract Etiology

Congenital Cataract

  • Chromosomal aberrations

    • Trisomy 13

    • Trisomy 18

    • Trisomy 21 a

      a Cataracts may not be noted until infancy or childhood

    • Turner syndrome a

  • Drug exposure during pregnancy

    • Chlorpromazine

    • Corticosteroids

    • Sulfonamides

  • Galactokinase deficiency

  • Galactose-1-phosphate uridyltransferase deficiency

  • Galactosemia

  • Genetic

    • Autosomal dominant inheritance

      • ▪

        Hereditary spherocytosis a

      • ▪

        Incontinentia pigmenti a

      • ▪

        Marshall syndrome a

      • ▪

        Myotonic dystrophy a

      • ▪

        Schäfer syndrome a

      • ▪

        Without other anomalies

    • Autosomal recessive inheritance

      • ▪

        Congenital ichthyosis a

      • ▪

        Congenital stippled epiphyses (Conradi disease)

      • ▪

        Marinesco-Sjögren syndrome a

      • ▪

        Siemens syndrome a

      • ▪

        Smith-Lemli-Opitz syndrome

    • X-linked inheritance (oculocerebrorenal syndrome) a

  • Idiopathic

    • Intrauterine infection a

    • Mumps

    • Rubella

    • Syphilis

  • Maternal factors

    • Diabetes

    • Malnutrition

    • Radiation

    • Prematurity

  • Syndromes of uncertain etiology

    • Hallermann-Streiff syndrome

Acquired Cataract

  • Drug-induced

    • Corticosteroids

    • Long-acting miotics

  • Genetic

    • Autosomal dominant inheritance (Alport syndrome)

    • Autosomal recessive inheritance

      • ▪

        Cockayne disease

      • ▪

        Hepatolenticular degeneration (Wilson disease)

      • ▪

        Rothmund-Thompson syndrome

      • ▪

        Werner syndrome

    • X-linked inheritance (pseudo-pseudohypoparathyroidism)

  • Chromosomal (Prader-Willi syndrome)

  • Metabolic

    • Cretinism

    • Hypocalcemia

    • Hypoparathyroidism

    • Juvenile diabetes

    • Pseudohypoparathyroidism

  • Trauma

  • Varicella (postnatal)

Dislocated Lens

  • Crouzon syndrome

  • Ehlers-Danlos syndrome

  • Homocystinuria

  • Hyperlysinemia

  • Marfan syndrome

  • Sturge-Weber syndrome

  • Sulfite oxidase deficiency

In previous studies, intrauterine infection accounted for one-third of congenital cataracts. That percentage has declined with the prevention of rubella embryopathy by immunization. Genetic and chromosomal disorders account for a significant number of cases, but in a large minority the cause is unknown. The mode of transmission of syndromic congenital cataracts varies. In many hereditary syndromes, cataracts can be either congenital or delayed in appearance until infancy, childhood, or even adulthood. Several of these syndromes are associated with dermatoses: incontinentia pigmenti (irregular skin pigmentation), Marshall syndrome (anhidrotic ectodermal dysplasia), hereditary mucoepithelial dysplasia, and congenital ichthyosis.

Congenital cataracts occur in approximately 10% of children with trisomy 13 and trisomy 18 and many children with trisomy 21. The association of congenital cataract and lactic acidosis or cardiomyopathy suggests a mitochondrial disorder.

Clinical features

Small cataracts may impair vision and may be difficult to detect by direct ophthalmoscopy. Large cataracts appear as a white mass in the pupil and, if left in place, quickly cause deprivation amblyopia. The initial size of a cataract does not predict its course; congenital cataracts may remain stationary or increase in density but never improve spontaneously. Other congenital ocular abnormalities, aniridia, coloboma, and microphthalmos occur in 40%–50% of newborns with congenital cataracts.

Diagnosis

Large cataracts are obvious on inspection. Smaller cataracts distort the normal red reflex when the direct ophthalmoscope is at arm’s length distance from the eye and a + 12 to + 20 lens is used.

Genetic disorders and maternal drug exposure are important considerations when cataracts are the only abnormality. Intrauterine disturbances, such as maternal illness and fetal infection, are usually associated with growth retardation and other malformations. Dysmorphic features are always an indication for ordering chromosome analysis. Galactosemia is suspected in children with hepatomegaly and milk intolerance (see Chapter 5 ), but cataracts may be present even before the development of systemic features.

Management

Developmental amblyopia is preventable by recognizing and removing cataracts before age 3 months. Urgent referral to a pediatric ophthalmologist is the standard of care.

Congenital Optic Nerve Hypoplasia

Optic nerve hypoplasia is a developmental defect in the number of optic nerve fibers and may result from excessive regression of retinal ganglion cell axons. Hypoplasia may be bilateral or unilateral and varies in severity. It may occur as an isolated defect or be associated with intracranial anomalies. The most common association is with midline defects of the septum pellucidum and hypothalamus (septo-optic dysplasia). The cause of septo-optic dysplasia is unknown in most cases, but some causative genetic mutations have been discovered.

Clinical features

The phenotype is highly variable; 62% of affected children have isolated hypopituitarism and 30% have the complete phenotype of pituitary hypoplasia, optic nerve hypoplasia, and agenesis of midline structures. In one study group of 55 patients with optic nerve hypoplasia, 49% had an abnormal septum pellucidum on magnetic resonance imaging (MRI), and 64% had a hypothalamic–pituitary axis abnormality. Twenty-seven patients (49%) had endocrine dysfunction, and 23 of these had a hypothalamic–pituitary axis abnormality. The frequency of endocrinopathy was higher in patients with an abnormal septum pellucidum (56%) than a normal septum pellucidum (39%) and the appearance of the septum pellucidum predicts the likely spectrum of endocrinopathy.

When hypoplasia is severe, the child is severely visually impaired and the eyes draw attention because of strabismus and nystagmus. Ophthalmoscopic examination reveals a small, pale nerve head ( Fig. 16.1 ). A pigmented area surrounded by a yellowish mottled halo is sometimes present at the edge of the disk margin, giving the appearance of a double ring. The degree of hypothalamic–pituitary involvement varies. Possible symptoms include neonatal hypoglycemia and seizures, recurrent hypoglycemia in childhood, growth retardation, diabetes insipidus, and sexual infantilism. Some combination of mental retardation, cerebral palsy, and epilepsy is often present and indicates malformations in other portions of the brain.

Fig. 16.1, Optic Nerve Hypoplasia.

Diagnosis

All infants with ophthalmoscopic evidence of optic nerve hypoplasia require cranial MRI and an assessment of endocrine status. The common findings on MRI are cavum septum pellucidum, hypoplasia of the cerebellum, aplasia of the corpus callosum, aplasia of the fornix, and an empty sella. Absence of the pituitary infundibulum with posterior pituitary ectopia indicates congenital hypopituitarism. Endocrine studies should include assays of growth hormone, antidiuretic hormone, and the integrity of hypothalamic–pituitary control of the thyroid, adrenal, and gonadal systems. Infants with hypoglycemia usually have growth hormone deficiency.

Superior segmental optic nerve hypoplasia is associated with congenital inferior visual field defects and occurs in children born to mothers with insulin-dependent diabetes.

Management

No treatment is available for optic nerve hypoplasia, but endocrine abnormalities respond to replacement therapy. Children with corticotrophin deficiency may experience sudden death. Children with visual impairment may benefit from visual aids.

Coloboma

Coloboma is a defect in embryogenesis that may affect only the disk or may include the retina, iris, ciliary body, and choroid. Colobomas isolated to the nerve head appear as deep excavations, deeper inferiorly. They may be unilateral or bilateral. The causes of congenital coloboma are genetic (monogenic and chromosomal) and intrauterine disease (toxic and infectious). Retinochoroidal colobomas are glistening white or yellow defects inferior or inferior nasal to the disk. The margins are distinct and surrounded by pigment. Morning glory disk is not a form of coloboma; it is an enlarged dysplastic disk with a white excavated center surrounded by an elevated annulus of pigmentary change. Retinal vessels enter and leave at the margin of the disk, giving the appearance of a morning glory flower. The morning glory syndrome is associated with transsphenoidal encephaloceles. Affected children are dysmorphic with midline facial anomalies.

Acute monocular or binocular blindness

The differential diagnoses of acute and progressive blindness show considerable overlap. Although older children recognize sudden visual loss, slowly progressive ocular disturbances may produce an asymptomatic decline until vision is severely disturbed, especially if unilateral. When finally noticed, the child’s loss of visual acuity seems acute. Teachers or parents are often the first to recognize a slowly progressive visual disturbance. Box 16.3 lists conditions in which visual acuity is normal and then suddenly lost. Box 16.4 lists disorders in which the underlying pathological process is progressive. Consult both lists in the differential diagnosis of acute blindness. The duration of a transitory monocular visual loss suggests the underlying cause: seconds indicate optic disk disorders such as papilledema or drusen, minutes indicate emboli, hours indicate migraine, and days indicate optic neuropathy, most commonly optic neuritis.

Box 16.3
Causes of Acute Loss of Vision

  • Carotid dissection a

    a Denotes the most common conditions and the ones with disease modifying treatments

    (see Chapter 11 )

  • Cortical blindness

    • Anoxic encephalopathy (see Chapter 2 )

    • Benign occipital epilepsy a (see Chapter 1 )

    • Hydrocephalus a

    • Hypoglycemia a

    • Hypertension a (malignant or accelerated)

    • Hyperviscosity

    • Hypotension

    • Migraine a (see Chapter 3 )

    • Occipital metastatic disease

    • Post-traumatic transient cerebral blindness

    • Systemic lupus erythematosus

    • Toxic a (cyclosporine, etc.)

    • Trauma

    • Disorders affecting the optic nerves

    • Optic neuropathy a

      • ▪

        Demyelinating

      • ▪

        Ischemic

      • ▪

        Toxic

      • ▪

        Traumatic

    • Pituitary apoplexy

    • Pseudotumor cerebri a (see Chapter 4 )

  • Retinal disease

    • Central retinal artery occlusion

    • Migraine

    • Trauma

Box 16.4
Causes of Progressive Loss of Vision

  • Compressive optic neuropathies

  • Disorders of the lens (see Box 16.3 )

    • Cataract

    • Dislocation of the lens

  • Hereditary optic atrophy

    • Leber hereditary optic neuropathy

    • Wolfram syndrome

  • Intraocular tumors

  • Tapetoretinal degenerations

    • Abnormal carbohydrate metabolism

      • ▪

        Mucopolysaccharidosis (see Chapter 5 )

      • ▪

        Primary hyperoxaluria

    • Abnormal lipid metabolism

    • Other syndromes of unknown etiology

      • ▪

        Bardet-Biedl syndrome

      • ▪

        Cockayne syndrome

      • ▪

        Laurence-Moon syndrome

      • ▪

        Refsum disease (see Chapter 7 )

      • ▪

        Usher syndrome (see Chapter 17 )

Cortical Blindness

Cortical blindness in children may be permanent or transitory, depending on the cause. The causes of transitory cortical blindness in childhood include migraine (see Chapter 3 ), mild head trauma, brief episodes of hypoglycemia or hypotension, and benign occipital epilepsy (see Chapter 1 ). Acute and sometimes permanent blindness may occur following anoxia; secondary to massive infarction of, or hemorrhage into, the visual cortex; and when multifocal metastatic tumors or abscesses are located in the occipital lobes. The main feature of cortical blindness is loss of vision with preservation of the pupillary light reflex. Fundoscopic examination is normal.

Hypoglycemia

Repeated episodes of acute cortical blindness may occur at the time of mild hypoglycemia in children with glycogen storage diseases and following insulin overdose in diabetic children.

Clinical features

Sudden blindness is associated with clinical evidence of hypoglycemia (sweating and confusion). Ophthalmoscopic and neurological findings are normal. Recovery is complete in 2–3 hours.

Diagnosis

During an episode of cortical blindness caused by hypoglycemia, electroencephalography (EEG) shows high-voltage slowing over both occipital lobes. Afterward the EEG returns to normal. Brain MRI shows diffuse edema in the occipital lobes.

Management

Recovery occurs when blood glucose concentration normalizes.

Transitory Post-Traumatic Cerebral Blindness

Clinical features

Transitory post-traumatic cerebral blindness is a benign syndrome that most often occurs in children with a history of migraine or epilepsy. The spectrum of visual disturbance is broad, but a juvenile and an adolescent pattern exist. In children younger than 8 years, the precipitating trauma is usually associated with either a brief loss of consciousness or a report that the child was “stunned.” The child claims blindness almost immediately on regaining consciousness, which lasts for an hour or less. During the episode, the child may be lethargic and irritable but is usually coherent. Recovery is complete, and the child may not recall the event.

In older children, a syndrome of blindness, confusion, and agitation begins several minutes or hours after trivial head trauma. Consciousness is not lost. All symptoms resolve after several hours, and the child has complete amnesia for the event. These episodes share many features with acute confusional migraine and are probably a variant of that disorder (see Chapter 2 ).

Diagnosis

Head computed tomography (CT) is invariable in children with any neurological abnormality following head trauma, but is probably unnecessary if the blindness has cleared. Those with persistent blindness require an MRI to exclude injury to the occipital lobes. Occipital intermittent rhythmic delta on EEG suggests migraine or epilepsy as the underlying cause. Recognition of the syndrome can avoid the trouble and expense of other studies. Scrutinize the family history for the possibility of migraine or epilepsy. The rapid and complete resolution of all symptoms confirms the diagnosis.

Management

Treatment is unnecessary if the symptoms resolve spontaneously.

Psychogenic Blindness

A spurious claim of complete binocular blindness is easy to identify. A pupillary response to light indicates that the anterior pathway is intact and only cortical blindness is a possibility. Simply observing the child’s visual behavior such as making eye contact, avoiding obstructions in the waiting room, and following nonverbal instructions, confirms effective visual capability. Otherwise, assess visual function by using a full-field optokinetic stimulus tape or by moving a large mirror in front of the patient to stimulate matching eye movements. In the case of psychogenic monocular blindness, perform the same tests with a patch covering the normal eye.

Spurious claims of partial visual impairment are more difficult to challenge. Helpful tests include observing visual behavior, failure of acuity to improve linearly with increasing test size, inappropriate ability to detect small test objects on a tangent screen, and constricted (tunnel) visual fields to confrontation.

Optic Neuropathies

Demyelinating Optic Neuropathy

Demyelination of the optic nerve (optic neuritis) may occur as an isolated finding affecting one or both eyes, or it may be associated with demyelination in other portions of the nervous system. Discussion of neuromyelitis optica (NMO; Devic syndrome ), the syndrome combining optic neuritis and transverse myelitis, is in Chapter 12 , and multiple sclerosis in Chapter 10 . MRI is a useful technique for surveying the central nervous system for demyelinating lesions (see Fig. 10.1 ). The incidence of later multiple sclerosis among children with optic neuritis is 15% or less if the child has no evidence of more diffuse involvement when brought to medical attention. The incidence is much higher when diffuse involvement is present or when optic neuritis recurs within 1 year. Unilateral optic neuritis, and retrobulbar as opposed to papillitis, has a higher incidence of later multiple sclerosis than bilateral optic neuritis.

Clinical features

Monocular involvement is characteristic of optic neuritis in adults, but binocular involvement occurs in more than half of children. Binocular involvement may be concurrent or sequential, sometimes occurring over a period of weeks. The initial feature in some children is pain in the eye, but for most it is blurred vision, progressing within hours or days to partial or complete blindness. Visual acuity reduces to less than 20/200 in almost all affected children within 1 week. A history of a preceding “viral” infection or immunization is common, but a cause-and-effect relationship between optic neuritis and these events is not established.

Results of ophthalmoscopic examination may be normal at the onset of symptoms if neuritis is primarily retrobulbar. Visual loss readily distinguishes papillitis from papilledema. In optic neuritis, visual loss occurs early; in papilledema, visual loss is a late feature.

Neuroretinitis is the association of swelling of the optic nerve head with macular edema or a macular star. Ophthalmoscopic examination shows disk swelling, peripapillary retinal detachment, and a macular star ( Fig. 16.2 ). Neuroretinitis suggests the possibility of conditions other than idiopathic optic neuritis.

Fig. 16.2, Neuroretinitis.

In the absence of myelitis, the prognosis in children with bilateral optic neuritis is good. Complete recovery occurs in the majority of those affected.

Diagnosis

Optic neuritis is a consideration whenever monocular or binocular blindness develops suddenly in a child. Ophthalmoscopic or slit-lamp examination confirms the diagnosis. Visual evoked response testing further confirms the diagnosis. MRI of the orbit may reveal swelling and demyelination of the optic nerve. Examination of the cerebrospinal fluid may be helpful to check for markers of demyelinating disease, such as oligoclonal bands, IgG index, and anti-NMO antibodies. Such examination sometimes shows a leukocytosis and an increased concentration of protein. Accelerated hypertension causes bilateral swelling of the optic nerves and recording blood pressure is an essential part of the evaluation.

Management

In adults, intravenous methylprednisolone, 250 mg every 6 hours for 3 days, followed by oral prednisone, 1 mg/kg/day for 11 days then tapering over 4 days, speeds the recovery of vision and reduces the recurrence of neuritis in the first 2 years according to the results of the optic neuritis treatment trial. The long-term outcome from optic neuritis is not significantly changed by the treatment. In children, we use intravenous methylprednisolone 3.5 mg/kg/dose q 6 hours for 3 days followed by 11 days of oral prednisone 1 mg/kg/day and then a tapering over 4 days.

Ischemic Optic Neuropathy

Infarction of the anterior portion of the optic nerve is rare in children and is usually associated with systemic vascular disease or hypotension.

Clinical features

Ischemic optic neuropathy usually occurs as a sudden segmental loss of vision in one eye, but slow or stepwise progression over several days is possible. Recurrent episodes are unusual except with migraine and some idiopathic cases.

Diagnosis

Altitudinal visual field defects are present in 70%–80% of patients. Color vision loss is roughly equivalent in severity to visual acuity loss, whereas in demyelinating optic neuritis the disturbance of color vision is greater than that of visual acuity. Ophthalmoscopic examination reveals diffuse or partial swelling of the optic disk. When swelling is diffuse, it gives the appearance of papilledema and flame-shaped hemorrhages appear adjacent to the disk margin. After acute swelling subsides, optic atrophy follows.

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