Normal Visual Development

The visual system is immature at birth. Achievement of normal vision is dependent on key anatomic changes during development that involve both the retina and the visual pathways. At the level of the retina, connections between the photoreceptors and the inner retinal cells are not fully formed until a few months after birth.1 At the level of the brain, myelination of the optic radiations takes place in the first year of life. Normal visual development also depends on well-focused input from the anterior segment of the eye. Hubel and Wiesel found that, if this normal input is not present, then visual deprivation leads to maldevelopment in the cerebral cortex.2

Vision Testing in Children

Estimates of visual acuity at birth range from 20/2000 to 20/400. A newborn starts fixating and regarding the mother’s face by 2 weeks of age. Between 8 and 10 weeks of age, a normal infant can generally fix and follow a large object over an arc of 180°. A visual problem exists if an infant cannot fix and follow a lighted toy by 3 months of age.

Normal ranges of visual acuity in children vary based on age. Methods to measure visual acuity are also age-dependent. In general, recognition acuity measures are favored over other methods (see “Recognition acuity tests: Allen pictures, HOTV and Snellen letters,” p. 380). To assess visual acuity in a preverbal child, motor behavioral responses can be used, such as optokinetic nystagmus or preferential looking tests. When needed, a visual evoked potential test can quantify the visual sensory response. Table 29-1 lists normal ranges of visual acuity by age using the preferential looking test or visual evoked potentials. When children are old enough to verbalize their responses, visual acuity is done by recognition acuity testing. If a child is too shy to talk, he or she can be asked to match pictures or letters with a hand-held card.

Examination Procedures and Guidelines for Referral

Optokinetic Nystagmus

This test consists of a cylindrical drum with alternating black and white rectangular stripes. The drum is rotated in the infant’s visual field while the examiner observes for smooth pursuit eye movements in the direction of the rotating drum followed by saccadic eye movements in the opposite direction. Horizontal saccades can be elicited at birth in a full-term child, but vertical saccades do not develop until 4 to 6 weeks of age.

Visual Evoked Potentials

Using scalp electrodes, electroencephalographic activity can be assessed while showing a child a specific visual pattern. Waveforms are compared to age-matched controls.

Preferential Looking Test

Infants prefer to look toward a pattern stimulus over a nonpattern homogenous single color (Figure 29-1). For this test, an operator holds a large card that carries a pattern on one side and is blank on the other. Through a central viewer the infant’s fixation movement can be observed—higher the grating (thinner the stripes of the pattern), the better the visual acuity measured.

Finding and Following Objects

A simple way of assessing visual function is to show a child a small toy or a familiar object such as a colorful piece of cereal. The examiner elicits the child’s determination to reach for the object of regard as well as the child’s ability to fix and follow the object as it is moved about in space. Fixation behavior can be assessed separately for each eye by using an eye patch.

Recognition Acuity Tests: Allen Pictures, Hotv, and Snellen Letters

Generally beginning at 2 to 3 years of age, a child can name or point to a matching card of familiar pictures (Lea symbols or Allen pictures). Older children can do this with the letters H, O, T, and V (Figure 29-2). Once children learn the alphabet, their vision can be assessed with the Snellen visual acuity chart. A visual acuity of 20/30 signifies that a child can identify a letter at 20 feet that a normal child, or adult, could identify at 30 feet.

Reasons for Referral to an Ophthalmologist

The basic eye examination for the non-ophthalmologist should include gross vision testing, external ocular examination, assessment of the red reflex, and the position of the corneal light reflex. Any abnormality of these tests should prompt a referral to an ophthalmologist. Checking for a red reflex is best performed with the examiner holding a direct ophthalmoscope about 30 cm away from the baby’s face and setting the dial on the ophthalmoscope at +8. The infant can be rocked gently or given a bottle to encourage opening of the eyes. Setting the ophthalmoscope to a slit beam sometimes gives a reflex that is easier to evaluate. A normal red reflex is bright orange in a blond infant and brownish-orange in a darkly pigmented infant. If the reflex is difficult to see because of a small pupil, the instillation of dilating drops can facilitate the examination.

Assessment of the corneal light reflex is done by holding a light source (preferably next to a toy to attract the child’s attention) and looking at the position of the light reflexes on the cornea. In a normal child the light will fall symmetrically on the nasal border of the pupil in each eye. If there is a strabismus present (see “Disorders of Ocular Motility” later in the chapter), the corneal light reflex will be asymmetrically located between the two eyes.

A particular condition that warrants referral to an ophthalmologist is nystagmus—an involuntary, rhythmic oscillatory movement of the eyes. The most benign form is congenital motor nystagmus that begins soon after birth and is not associated with a visual or neurological disorder. A sensory nystagmus is due to a visual pathway dysfunction, usually due to an abnormality of the retina or optic nerve as detected by a dilated eye examination. In the rare cases where the dilated eye examination is normal, an electroretinogram (ERG) may assist in the diagnosis. New-onset nystagmus requires neuroimaging.3

General aspects of the eye examination that can be performed by a non-ophthalmologist are outlined in Table 29-2.

Ocular Causes of Decreased Visual Acuity in Children

Based on data from the American Schools for the Blind, in the United States the most common causes of poor vision in children are cortical visual impairment (19%), retinopathy of prematurity (13%), and optic nerve hypoplasia (5%). In developing countries, the World Health Organization estimates that 500,000 people are born blind each year, of which 50% to 90% die mostly due to malnutrition. Thirty percent to seventy percent of childhood blindness is preventable, and the leading causes are corneal opacities or other anterior segment anomalies due to systemic diseases such as measles, congenital rubella, ophthalmia neonaturum, vitamin A deficiency, or side effects from traditional eye medications.4

Anomalies of the Anterior Segment of the Eye

The anterior segment of the eye consists of the cornea, anterior chamber, iris, and crystalline lens. The main function of these structures is to focus light onto the retina. Refractive errors or opacities in the media result in a blurred image. It is important to diagnose and treat these problems at an early age to prevent amblyopia. A congenital cataract that is visually significant should be surgically treated in the first few months of life to prevent severe visual loss and nystagmus. An excellent screening test for media opacities in children is assessing the red reflex (Table 29-3, Figure 29-3). Corneal infections, such as with herpes simplex virus, or trauma resulting in corneal scarring can also result in decreased visual acuity in children, and these problems can be compounded by amblyopia (see section entitled “Amblyopia,” p. 384).

Congenital Cataracts

A cataract is an opacification of the crystalline lens. It occurs in 1 in 4000 to 10,000 live-born infants. It may be unilateral or bilateral, and may be part of an ocular or systemic syndrome. Surgical removal is warranted when the cataract is visually significant (ie, when the opacity is central and larger than 3 mm in size). Smaller partial cataracts may be managed with pharmacologic pupillary dilation. The visual outcome of congenital cataracts has significantly improved over the past few decades with the advent of newer surgical techniques. Surgery should be performed as soon as the diagnosis is made to prevent irreversible, severe amblyopia. Congenital cataracts may be a familial condition; therefore screening the proband’s family members (especially young siblings) for an asymptomatic cataract is recommended. Screening for galactosemia, a treatable systemic disease, is advisable in cases of a congenital cataract. However, routine testing for toxoplasmosis, other agents, rubella, cytomegalovirus, and herpes simplex (TORCH) is controversial and recommended by some only if there are systemic findings suggestive of an infection.5

Congenital Glaucoma

Glaucoma is an increase in the intraocular pressure causing damage to the optic nerve. Untreated it may cause irreversible vision loss. The most common type of pediatric glaucoma is primary congenital glaucoma, which has an incidence of 1 in 10,000. The primary pathology in congenital glaucoma is intrinsic disease of the aqueous outflow system. A child with congenital glaucoma will present with a large and cloudy cornea, tearing (epiphora), and photophobia. However, the symptoms may vary in severity ranging from pure tearing and photophobia to a very large, cloudy cornea (bupophthalmos).5,6

Coloboma

A coloboma is caused by a failure of the embryonic fissure to close. It may involve the eyelid, anterior segment, retina, or optic nerve. Not all colobomas lead to visual impairment. For example, an iris coloboma results in a keyhole-shaped pupil with no reduction in vision. In comparison, a coloboma of the fundus will often have associated visual impairment because of retinal dysplasia, particularly if the macula is involved. Patients with retinal colobomas are advised to have a dilated eye examination twice a year because of an increased risk for retinal holes and detachments. Colobomas may be part of the CHARGE syndrome (coloboma, heart anomalies, choanal atresia, retardation of growth and development, and genital and ear anomalies), an autosomal dominant disorder.5

Other Rare Anterior Segment Anomalies

Anomalies of the anterior segment of the eye can be isolated or accompanied by systemic abnormalities. There will be a blunted red reflex similar to a congenital cataract. Persistant hyperplastic primary vitreous can be seen in children born of mothers who have consumed cocaine. It often presents as a small eye with a unilateral cataract, microcephaly, and mental retardation. Anterior segment dysgenesis is a spectrum of abnormalities involving the cornea, iris, and lens due to dysembryogenensis associated with systemic findings such as facial dysmorphism, skin and dental abnormalities, and chromosomal anomalies. A dermoid is a white, elevated lesion that can encroach on the cornea, causing astigmatism or occlusion of the visual axis. It may be a manifestation of Goldenhar syndrome (oculo–auricular–vertebral syndrome), consisting of vertebral anomalies, small ears with skin tags, and facial dysmorphism. Aniridia (absence of the iris) may be associated with multiple ocular anomalies including glaucoma, macular hypoplasia, and nystagmus. It can have a familial autosomal dominant or sporadic inheritance pattern. The sporadic type may be associated with Wilms tumor, genitourinary anomalies, and mental retardation (WAGR syndrome). Microphthalmia is defined as a small eyeball with no structural defect. Vision is often affected because of the presence of other ocular anomalies. Microphthalmia can be a manifestation of an intrauterine infection or trisomy 13 or 18.5

Anomalies of the Vitreous and Retina

The main chamber of the eye is the vitreous cavity, which is filled with a jelly-like substance called the vitreous. The retina is the neurosensory structure of the eye that captures light and transmits a signal to the brain through the optic nerves.

Vitreous Hemorrhage

There are multiple causes of a vitreous hemorrhage, but in children the most common causes are retinopathy of prematurity, retinal vessel pathology, ocular trauma, shaken baby syndrome, or an intracranial hemorrhage (Terson syndrome). A vitreous hemorrhage becomes visually significant when it blocks the visual axis. It often resolves spontaneously over several months, but observation is warranted to prevent amblyopia. In persistent cases a vitrectomy is performed. The final visual outcome is dependent on the extent of the disease, with penetrating eye trauma carrying the worst prognosis.7

Retinal Dystrophies

Retinitis pigmentosa (RP) is a term used for a broad category of diseases affecting the retinal photoreceptor cells (rods and cones). The incidence of primary photoreceptor cell anomalies is 1 in 3000 to 5000. More than 100 genes have been implicated in RP. Of the inherited RP syndromes, recessive X-linked RP is the most common inheritance pattern seen.8 Typically, visual dysfunction begins with night blindness (nyctalopia) and visual field constriction progressing to decreased central visual acuity. Pigment deposits in a “bone spicule” formation are often seen in the peripheral retina. An ERG can help establish the diagnosis and monitor disease progression. Although there is no cure, vitamin A, palmitate, and omega-3-rich fish may slow the progression of the disease. Systemic diseases associated with RP include Usher syndrome, Laurence-Moon-Bardet-Biedl syndrome, and Kearns-Sayre syndrome. Usher syndrome is characterized by sensorineural hearing loss of variable severity and onset. Patients with Laurence-Moon-Bardet-Biedl syndrome have truncal obesity, renal dysfunction, polydactyly, and short stature. Kearns-Sayre syndrome is a mitochondrial myopathy characterized by external ophthalmolplegia, ptosis, and cardiac conduction block.8 Congenital stationary night blindness (CSNB) is a retinal dystrophy characterized by decreased vision at night. It is associated with high myopia and fundus pigmentation that is similar to RP; however, CSNB is a nonprogressive disorder.9

Leber congenital amaurosis (LCA) is an autosomal recessive disorder characterized by blindness before 6 months of age. It is the cause of approximately 10% to 18% of cases of congenital blindness. The ERG is severely attenuated. Final visual acuity in LCA patients ranges from no light perception to 20/200. Systemic findings in children with LCA include polycystic kidneys, osteoporosis, cleft palate, and skeletal and brain anomalies.9,10

Retinopathy of Prematurity

Retinopathy of prematurity (ROP) affects premature and low birth weight babies of less than 32 weeks gestation or less than 1251 g, respectively. It is a complex disorder of prematurity caused by the disruption of the normal intrauterine growth of the retina. Management of ROP starts in the nursery with a screening examination to monitor the growth of the retinal vessels. In appropriate cases, treatment is initiated with laser photoablation to the peripheral retina to decrease the probability of a retinal detachment. A vitrectomy is often indicated in cases of severe disease and retinal detachment.

Genetic and Metabolic Disorders Causing a Decrease in Vision

Sometimes, clinical symptoms and findings on ocular examination may provide clues to the presence of a genetic or metabolic disease. Many metabolic diseases can manifest with accumulation of toxic by-products in the cornea, lens, or retina.

Corneal Disorders

The cornea may become opacified in a variety of genetic disorders. In mucopolysaccharidoses (MPS), the cornea is cloudy due to the deposition of glycosaminoglycans in the corneal stroma. Corneal transplant may be required in MPS IV (Morquio), MPS VI (Maroteaux-Lamy), and less commonly in MPS III (Sanfilippo).11 Other disorders known to cause deposits in the cornea include mucoliposes, Gaucher disease, cystinosis, tyrosinemia, and sphingolipidoses including the juvenile form of metachromatic leukodystrophy. In Wilson disease, alkaptonuria and dyslipoproteinemias deposits occur at the corneal limbus with no effect on vision.

Corneal opacification can be seen in a number of hereditary corneal dystrophies that do not have systemic manifestations (eg, congenital hereditary corneal dystrophies). They usually manifest in late childhood and are characterized by deposits in the cornea that progressively affect vision.

Enlargement of the cornea (megalocornea) can be seen in Marfan syndrome or Ehlers-Danlos syndrome. An abnormally shaped cornea (keratoconus) causing severe astigmatism and scarring is associated with osteogenesis imperfecta and Ehlers-Danlos syndrome.

The cornea is a very sensitive structure and disorders causing corneal exposure or dryness must be managed very carefully to prevent excessive corneal dryness and subsequent infections, scarring, and vision loss.

Lenticular Disorders

The lens may opacify due to a variety of metabolic disorders, such as diabetes mellitus, galactosemia, galactokinase deficiency, and Fabry syndrome. Marfan syndrome and homocystenuria is associated with subluxation of the lens.

Retinal Disorders

The macular area is devoid of ganglion cells; therefore, in cases of lipid accumulation or edema of the ganglion cell layer, the macula still displays a red choroidal color, giving the look of a red spot surrounded by white retina—clinically described as a cherry red spot. A cherry red spot is most commonly seen following an ischemic or vaso-occlusive event in both adults and children but may also be seen in Tay-Sachs or Sandhoff disease, metachromatic leukodystrophy, and Niemann-Pick disease. Mucopolysccharidoses, mucolipidosis, gangliosidoses, and peroxisomal disorders can also show retinal pigment changes similar to RP.12

Congenital Optic Nerve Anomalies

Congenital optic nerve disorders include but are not limited to optic nerve hypoplasia, autosomal dominant optic atrophy, hereditary optic neuropathy of Leber, and morning glory disc anomaly. Children with an optic nerve anomaly may have vision ranging from normal to complete blindness. Anomalies of the optic nerve may be associated with anterior segment, retinal, brain, or other systemic abnormalities.

Optic Nerve Hypoplasia

Optic nerve hypoplasia (ONH) is the most common congenital optic nerve anomaly. In addition to the appearance of a small nerve, signs of ONH on examination include a “double ring” sign (with the larger ring being the scleral canal and the smaller ring the actual nerve tissue) and anomalous vascular branching pattern. Patients might be asymptomatic in mild cases or they may present with poor vision, nystagmus, strabismus, or a combination of these. Bilateral cases, more commonly than unilateral cases, are associated with congenital malformation of the central nervous system and pituitary axis (septo-optic dysplasia). In these cases, magnetic resonance imaging (MRI) may show an absent infundibular stalk, ectopic bright spot in the hypothalamus, and an absent corpus callosum and septum pellucidum. A particular syndrome associated with ONH is DeMorsier syndrome, which is characterized by a combination of septo-optic dysplasia, facial dysmorphism, and an open anterior fontanel. Patients with DeMorsier syndrome may present with pituitary axis disruption including sudden death due to corticotropin deficiency.5,13

Morning Glory Disc Anomaly

Usually a unilateral condition, a morning glory disc is an enlarged optic nerve in the shape of a funnel with an indistinct border surrounded by depigmented areas, giving the appearance of the morning glory flower. It may be associated with a basal encephalocele in patients with midline defects, Moyamoya vascular disorder,14 and papillorenal disorder. The presentation and management of morning glory disc is similar to ONH.5,13

Autosomal Dominant Optic Atrophy

Autosomal dominant optic atrophy (ADOA) presents with vision loss in the first or second decade of life. Visual acuity may range from 20/20 to 20/200, with some affected individuals visually asymptomatic. Patients with ADOA may have a concomitant blue-yellow color blindness (tritanopia) and visual field testing showing a centrocecal or paracentral scotoma.5

Autosomal Recessive Optic Atrophy

Autosomal recessive optic atrophy (AROA) is a more severe condition than ADOA. It presents in infancy with rapid, progressive vision loss followed by a stabilization of visual acuity. Although it can be isolated, AROA is usually associated with other neurological disorders such as Behr and Costeff syndromes. Behr syndrome manifests with AROA associated with ataxia, spinocerebellar degeneration, and mental retardation. Costeff optic atrophy syndrome or type III 3-methyglucaconic aciduria presents with bilateral optic atrophy, spasticity, extrapyramidal dysfunction, and cognitive dysfunction.5

Amblyopia

The causes of amblyopia are ocular but pathophysiology is within the central nervous system. Amblyopia is defined as a decrease in visual acuity despite best refractive correction with no organic ocular abnormality seen on examination. Amblyopia can be unilateral or bilateral, and is caused by the lack of a clear image directed onto the retina during visual development. Image blur can be refractive, strabismic, or anatomic in origin. Refractive amblyopia is due to an uncorrected refractive error in one or both eyes, or a difference in refractive error between the two eyes (anisometropia). Strabismic amblyopia is due to early-onset strabismus (see “Disorders of Ocular Motility” later in the chapter) resulting in visual suppression. Deprivational amblyopia is due to ptosis or media opacity of the cornea, lens, or vitreous.

Young children (under the age of 8) are the most susceptible to amblyopia. Congenital media opacities should be treated as early as possible to prevent severe visual loss. Children usually do not complain of decreased vision, especially when it is unilateral; therefore, amblyopia can be overlooked and only detected when there is a noticeable strabismus or during a screening eye examination.

Treatment of amblyopia begins by removing any media opacity and providing the appropriate refractive correction in spectacles. The mainstay of amblyopia treatment is penalization of the fellow eye, either by patching or by cycloplegia with atropine eye drops (Figure 29-4). One large study showed that children with amblyopia may still respond to treatment up to age 17 years, especially if they have not been previously treated.15 However, results are generally better when treatment is started at younger ages.16