Normal Visual System in Infants and Children

Although the gross anatomy of the eye is similar at all ages, important differences exist between the eye of a young child and an adult. For example, the volumetric relationship between the eye and the orbit is dramatically different in children.

In infants, the choroid gives a blue hue to the overlying thin sclera. In white persons, the iris is often poorly pigmented at birth, and the final eye color may not be established until at least 8 months of age. Examination by direct ophthalmoscopy shows the baby’s fundus to be pale, with the macula barely visible. As the child gets older, the fundus becomes darker, and the macula becomes darker than the surrounding retina. The macula then displays the easily recognized oval, bright reflection of the ophthalmoscope light, known as the macular umbo (Plate 8–1).

The birth process can be somewhat traumatic to the eyes. Many newborns sustain episcleral and retinal hemorrhages during vaginal delivery (see Fig. 4-14). These hemorrhages can be alarming to both parents and physicians but are harmless and usually disappear within 2 weeks. At birth, the nasolacrimal duct often is blocked at its junction with the nasal mucosa under the inferior turbinate. The blockage resolves spontaneously in more than 90% of cases, although it can remain until 1 year of age in some children, causing persistent tearing. A few affected children then need surgical treatment.

The process and rate of development of vision in infants are better understood than they were 10 years ago. Vision exists in several forms with different neuronal channels carrying specific visual functions, such as contrast sensitivity, orientation, movement, and hyperacuity. Each function develops at a different rate. For practical purposes, normal newborns can see a human face easily and demonstrate their visual ability by looking at it; they even follow the face with eye or head movement as it passes slowly before them at close range (Fig. 8-1). A baby’s ability to follow your face can be verified only when the baby is awake and alert, often just before or in the middle of a feeding session. This innate ability is paramount to the infant’s future development because few parents fail to form an emotional attachment to a little one who looks directly at them minutes after birth. By contrast, parents of a blind or strabismic infant who are unable to establish the interaction that comes with normal eye contact may have significantly greater difficulty developing the same level of emotional attachment to their offspring.

FIGURE 8-1 Face follow vision testing of a young infant. A, Hold the child at arm’s length with the head comfortably supported. The examiner’s face is lined up with the apparent direction of gaze of the child. B, Move your face slowly to the side and observe the response. This 2-month-old boy now has a good face follow; he received his contact lenses 2 weeks after cataract surgery.

By 3 months of age, babies enjoy looking at the human mouth and eyes and at simple, colored toys. A 1-year-old toddler’s vision is about half as good as the best attainable adult score. Three-year-olds can see at least 6/9 (or 20/30 in the American system) in each eye, and their visual acuity can be tested with charts specially designed for them (see the section in this chapter on the LH test). The numerical ratio 20/30 actually indicates that a 3-year-old can see at 20 feet what the average adult sees at 30 feet.

Color vision is present from an early age. Newborns have color vision, although it is less sensitive than that of older infants. Newborns do not see faint colors well, if at all, but by 3 months of age, definite trichromatism is established. Babies of this age can differentiate between red, green, and yellow.

Binocularity, which confers the ability to see in three dimensions, has been proven to exist by 3 months of age, coinciding with the time the eyes finally maintain good alignment. This finding underlines the clinical significance of any persistent deviation of the eyes after age 3 months.

Eye movements may appear irregular, unbalanced, or disconjugate until the third month of life. Healthy newborns can display tonic movements of the eyes downward or upward. Sometimes, the eyes turn toward (esotropia) or away (exotropia) from each other.

Pupillary movements are limited in the newborn and are almost impossible to examine thoroughly at that age. A good pupillary examination in older children demands cooperation and patience, because children can rarely stare fixedly at a distant target while an observer tries to evaluate their pupils by shining a bright light in them. The children look either at the light or anywhere else and change their accommodation continuously, keeping their pupillary diameter in constant flux and possibly preventing adequate assessment of light-induced responses.

Accommodation in the newborn is limited. From a practical viewpoint, consider the newborn’s focus as stuck at an adult arm’s length. Within a few months after birth, focus improves, and the child’s accommodative amplitude soon reaches remarkable proportions. For example, a 5-year-old can clearly see a plane in the sky and then switch in a fraction of a second to look with great intensity at the details of a tiny spider close at hand. Unfortunately, this marvelous accommodative ability does not last forever.

Finally, a word on media transparency. The extraordinary transparency of all the optical parts of the child’s eye provides the observer with a crisp and bright image of the retina when viewed up close with the direct ophthalmoscope (a difficult but rewarding technique ). It also enables the clinician to critically assess the integrity of the eye with the very simple red pupillary image (reflex) test. In the right conditions, a bright coloration in the pupil provides a clear path for a light beam to enter the eye, hit the retina, and bounce back. This is the reason why photo shots can become prime screening tools to detect severe eye diseases.

Definition of terms

As an aid to diagnosis, this section contains a brief glossary of diagnostic terms that summarize the features to look for in children with eye problems. Box 8-1 and Figure 8-2 show the tools used to examine the eyes; Table 8-1 lists definitions and acronyms.

Box 8-1 Equipment Needed to Perform an Adequate Pediatric Eye Examination

Essential (see Fig. 8-2)

• Your face (preferably without glasses)

• Direct ophthalmoscope

• Other portable focal source of light (an otoscope is good)

• Red open-faced rubber nipple (to stick on top of focal light source for a bright red object)

• LH vision kit with tape for eye occlusion

• Tropicamide (1%) short-acting mydriatic (weak cycloplegic) drops

Ancillary

• Optokinetic nystagmus strip (a necktie with stripes will do)

• Fluorescein strips with loupes and cobalt-blue light

• Food (or a nursing mother)

FIGURE 8-2 Equipment for evaluating the visual system in children: your face, ophthalmoscope, otoscope, red nipple, visual acuity test kit, and short-acting mydriatic agent (tropicamide 1%).

Table 8-1 Ophthalmologic Shorthand*

Abbreviation/Acronym	Definition
Alt	Alternating strabismus; in almost all cases of strabismus, fixation (use of the eye to look at something) is with at least one eye at a time; if there is equal vision, the eyes will alternate fixation
APD	Afferent pupillary defect
CD	Corneal diameter
C/D ratio	Cup/disc ratio (cup size can be enlarged in persons with glaucoma)
CL	Contact lens
Comit	Comitant
E	Esophoria; the eye turns in only when there is interference with binocular vision (as with covering)
ET	Esotropia; one eye is turned in spontaneously
E(T)	Intermittent esotropia; the eye turns in only occasionally
IOL	Intra-ocular lens
IOP	Intra-ocular pressure
OD	Oculus dexter (Latin); right eye (English)
OS	Oculus sinister (Latin); left eye (English)
OU	Oculus uterque (Latin); each eye (English)
PERLA	Pupils equally reactive to light and accommodation
SLE	Slit-lamp examination
VA cc	Visual acuity with correction (with glasses or contact lens[es])
VA sc	Visual acuity without correction
X	Exophoria
XT	Exotropia; one eye turns out (exodeviation)
X(T)	Intermittent exotropia; the eye turns out only occasionally

* For example, a diagnosis of strabismus could be written as “Alt Comit X(T),” which would mean “alternating comitant intermittent exotropia.”

Amblyopia

Decreased vision in one or both eyes when no detectable or residual uncorrected organic or optical anomaly remains. Amblyopia is reversible if treated early enough (well before 9 years of age). It is severe if it develops early, as when it is caused by a congenital cataract or congenital ptosis. Occlusion amblyopia can occur if treatment such as patching of the sound (good) eye is too prolonged.

Blindness

Legal blindness is defined as vision of 6/60 (20/200) or less. Most assistance agencies for visually handicapped children use 6/24 (20/70) as the maximum vision cutoff for registration for their services. The leading causes of blindness vary dramatically in different regions of the world. Malnutrition, onchocerciasis, and trachoma are the culprits in many developing countries, whereas macular degeneration, glaucoma, diabetic retinopathy, amblyopia, trauma, and corneal herpes are generally responsible for legal blindness in developed countries. Eye injuries by BB guns are a leading cause of traumatic blindness in North American children, and many medical professional groups have proposed that these guns be regulated by legislation. Amblyopia, with a prevalence rate of 4% to 5%, is a significant cause of monocular blindness. Genetic diseases (involving mainly the optic nerve and retina), birth injury, and congenital defects (cataracts being the most common) are important causes of blindness in North American children, as are retinitis pigmentosa and albinism. With increasing survival of very low birth weight infants, retinopathy of prematurity (ROP) and optic nerve atrophy are making a comeback as significant causes of visual loss in children.

Cataracts

Cataracts are an important cause of leukocoria (white pupil, from the Greek; see Plate 8–2). Causes of pediatric cataracts include congenital rubella, metabolic disorders, and chromosomal anomalies. Cataracts can result from ocular inflammation (uveitis) or may accompany other ocular malformations. Many idiopathic cataracts are sporadic, but some are genetic. Some systemically administered medications cause cataracts. Steroids are common culprits, and they can cause glaucoma as well. Amblyopia in a child with a cataract is severe; therefore, cataracts in infants need immediate attention. Postoperative optical correction may require the use of contact lenses in infants, although intraocular lenses are becoming more popular in children older than 2 years.

Coloboma

A defect of closure of the embryonic fissure of the eye; hence, its inferonasal location in the eye. In mild form, only the iris is involved; in more severe cases, the choroid and the optic nerve can be involved (Plate 8–3). With optic nerve involvement, central nervous system (CNS) midline defects should be suspected, as in optic nerve hypoplasia (see definition of this term).

Epicanthal fold (pseudostrabismus)

Skin folds hiding nasal sclera. When the child looks sideways, the appearance of a misalignment can be dramatic. This is so-called pseudostrabismus, (see Plate 7-11, C) and it is an extremely common condition.

Esophoria and esotropia

Forms of strabismus in which the eyes deviate toward the nose. One eye is often the preferred one, implying a strong possibility of amblyopia in the nonpreferred eye. Alternating fixation suggests that vision in the two eyes may be equal. The visual inferences from the fixation pattern apply to all forms of strabismus. Some esotropias, due to accommodative factors, are amenable to optical treatment (i.e., glasses). Most cases of esodeviation are partially accommodative and require a combined treatment with glasses and surgical correction. A tropia is a strabismus present at the time of the observation, whereas a phoria is a tendency toward a particular type of strabismus. A phoria can be seen only when the eyes do not fuse or are prevented from doing so (e.g., by a patch over one eye). Fatigue or daydreaming can elicit a phoria as well.

Glaucoma (infantile or congenital)

A rare but important ocular disease often manifesting as tearing and photophobia (i.e., an inability to tolerate normal daylight). Glaucoma can be mistaken for lacrimal duct obstruction, but the accompanying photophobia and increased corneal size help make the correct diagnosis. Treatment is urgent and often surgical. Amblyopia also is associated with glaucoma.

Head tilt

Abnormal head positions can be induced by a large array of conditions, many of them ocular. Typical is the compensatory head tilt seen in a fourth cranial (trochlear) nerve palsy, which is assumed to avoid diplopia and keep the eyes aligned. Without the tilt, the eyes show a vertical strabismus and the patient sees double (Fig. 8-3, A).

FIGURE 8-3 Abnormal head postures. A, Tilt to the right in a fourth cranial (trochlear) nerve palsy. B, Child turns head to the left to avoid diplopia caused by a left sixth cranial nerve palsy (the patient turns the head toward the side of the palsy).

Head turn

An abnormal head position taken when reading or looking at a small visual target, typically caused by either a sixth cranial nerve (abducens) palsy or nystagmus. In the former, the head turn is used to avoid horizontal diplopia (Fig. 8-3, B); in the latter, the head turn improves vision by reducing nystagmic oscillations (null position).

Hemangioma (orbital, capillary)

Benign congenital tumors that grow rapidly when a child is between 1 and 6 months of age but tend to regress spontaneously later (Plate 8–4). Benign congenital tumors may cause severe amblyopia by pupillary obstruction, high astigmatism, or both. Early treatment is essential to preserve vision. Injection of steroids into the tumor, systemic treatment, glasses, and patching of the sound eye all may be necessary.

Hyperphoria, hypophoria, hypertropia, hypotropia

Vertical ocular deviations.

Hyphema

Bleeding into the eye’s anterior chamber (Plate 8–5). A trauma severe enough to cause a hyphema can involve other eye structures, leading to retinal detachment or injuring the trabecular meshwork of the iridocorneal angle and thereby causing glaucoma. Hyphema is the principal diagnosis in one third of eye traumas and is a major cause of ocular morbidity in children. Hyphemas rebleed in 6% of cases within 5 days of onset, causing further complications, but it may be possible to prevent rebleeding by decreasing physical activity and, in very selected cases, by administering systemic antifibrinolytic agents.

Laceration (cornea or globe)

A cut through the protective shell of the eye. Suspect a laceration if there is a history of trauma with a sharp object (a forceful blunt impact also can rupture the globe). Do not try to pry the lids open; doing so might expel the contents of the globe. Repair of a simple laceration of the cornea can be followed by astigmatism, an amblyogenic factor necessitating further intensive treatment, including contact lenses and patching.

Lacrimal duct obstruction (congenital)

Lacrimal duct obstruction is benign but is included in the differential diagnosis with congenital glaucoma. It resolves spontaneously in 90% of children by age 12 months but rarely thereafter.

Leukocoria

A white pupil (Plate 8–2). This finding has major clinical implications. The differential diagnosis includes retinoblastoma and cataract. Delaying treatment of the former leads to death; delaying treatment of a cataract causes permanent loss of vision.

Lymphangioma

A diffuse benign tumor of the orbit that often bleeds internally and is another cause of ptosis, proptosis, or both. Almost impossible to resect completely in childhood, lymphangioma is a cause of astigmatism and amblyopia (Fig. 8-4).

FIGURE 8-4 Lymphangioma of the right orbit with poor vision due to astigmatism caused by the mass effect of the lesion on the shape of the eye.

Myelinated nerve fiber layer

Abnormal presence of myelin around the superficial nerve fibers of the retina near the optic disc (Plate 8–6). It can be so extensive that the pupillary red reflex can be made to appear white (leukocoria). The vision is generally normal except when the macula is heavily involved.

Nystagmus

A descriptive term for jiggly, unstable, wiggly, or trembling eyes. In up to 90% of cases, an ophthalmic cause of nystagmus can be identified. It is mainly found when vision has been poor since early in life. Most causes are sensory, affecting the anterior visual pathway. The causes can be retinal (cone dystrophy, early retinitis pigmentosa, or congenital retinal toxoplasmosis scar); neuronal (optic nerve anomalies or early dystrophies); ectodermal (various forms of albinism); or even optical (cataract or corneal anomalies). In persons with nystagmus, the type of movement often is not indicative of any particular cause.

Ophthalmia neonatorum

In North America, neonatal ophthalmia once was principally caused by gonorrheal infection. Now, the most common causative organism is Chlamydia trachomatis. Staphylococcus pyogenes may cause outbreaks of conjunctivitis in newborn nurseries. Transient chemical conjunctivitis normally occurs after 1% silver nitrate prophylaxis in the newborn. The best agent for prophylaxis of gonococcal and chlamydial ophthalmia neonatorum continues to be debated.

Optic nerve hypoplasia

A common cause of congenital blindness in children. Optic nerve hypoplasia often is misdiagnosed as optic atrophy because secondary nystagmus (sensory) makes the hypoplasia difficult to visualize. The optic nerve head (disc) is smaller than normal (Plate 8–7). Look for CNS midline defects, including the involvement of the hypothalamic-pituitary axis with accompanying growth hormone deficiency (see Chapter 16).

Palsies (sixth, third, and fourth cranial nerves)

The extraocular muscles are innervated by various cranial nerves: the superior oblique by the fourth cranial nerve (also called the trochlear); the lateral rectus by the sixth cranial nerve; and all the others by the oculomotor nerve, the third cranial nerve, which also innervates the pupil and the ciliary body for accommodation. Any injury to these nerves induces a strabismus, the angle of which varies according to the direction of gaze—an incomitant strabismus. Typically, a head turn is seen in persons with sixth nerve palsy and lid ptosis in persons with third nerve palsy. Fourth cranial nerve palsy (trochlear) causes an ipsilateral hyperdeviation and a contralateral head tilt (see Fig. 8-3).

Periorbital cellulitis

Any inflammation around the orbit is cause for concern, and the differential diagnosis should include rhabdomyosarcoma (see later definition). When the orbital content is involved, ocular motility is decreased and the patient is at imminent risk of loss of vision. Haemophilus influenzae meningitis is an early complication in children younger than 5 years. Periorbital cellulitis (Plate 8–8) is most often associated with ethmoiditis in children who do not have a clear history of skin trauma or infection around the eye, and both computed tomography scanning and magnetic resonance imaging are invaluable for a clear evaluation of the best therapeutic regimen. This condition is far less common in areas of the world where Haemophilus influenzae B vaccine is used. Most cases of periorbital cellulitis require systemic antibiotic therapy.

Persistent hyperplastic primary vitreous (PHPV)

The presence of a unilateral dense residual vascularized glial frond of tissue that originates from the optic nerve disc and projects toward the back of the lens. It is the first tissue present in the eye required to initiate the growth of the lens. In PHPV, the lens is abnormal and cataractous, causing a leukocoria; the differential diagnosis of leukocoria includes other forms of cataract and retinoblastoma. PHPV is associated with microphthalmos and cataracts. The vessels in the back of the lens can bleed, inducing a very rare but diagnostic hemorrhagic cataract. PHPV is a progressive malformation that requires early surgery to save the eye and possibly restore its vision (Fig. 8-5).

FIGURE 8-5 Persistent hyperplastic primary vitreous is a cause of cataract. The fibrotic nature of the vascular membrane present behind the lens (the hyperplastic primary vitreous) causes traction of the ciliary processes, which become visible once the pupil is dilated.

Plexiform neurofibroma

A type of hamartomatous formation found in persons with neurofibromatosis. In the orbit, it is accompanied by sphenoid bone defects with herniation of the contents of the anterior fossa into the orbital cavity. This condition may or may not cause visual problems, such as strabismus, astigmatism, and optic nerve dysfunction (Fig. 8-6).

FIGURE 8-6 Plexiform neurofibroma of the left upper orbit. Such a hamartoma most often displaces the eye down, but in this case, the neurofibroma has not induced any strabismus; the corneal light reflexes are symmetric. Note the fullness of both upper and, to a smaller extent, lower lids.

Refractive amblyopia

Amblyopia is caused by the blurred image of a poorly focused eye (hyperopia, myopia, or astigmatism). This condition is found most commonly in 3- to 4-year-olds.

Retinitis pigmentosa

A generic term describing a variety of retinal degenerations, including choroidal degenerations, diseases of either type of photoreceptors, and syndromes involving other organ systems (e.g., Laurence-Moon-Biedl and Alström syndromes in which progressive retinal degeneration is associated with obesity and other systemic dysfunctions) (Plate 8–9). Most patients with retinitis pigmentosa experience a severe visual deficit at an early age.

Retinoblastoma

The most important cause of unilateral or bilateral leukocoria, retinoblastoma occurs in 1 in 15,000 births and often is also present with a strabismus or a red eye (Plate 8–10). The gene for this condition is located on the long arm of chromosome 13. Retinoblastoma is most curable if diagnosed early. Later death from a second malignancy is a major concern in bilateral and autosomal dominant familial cases.

Retinopathy of prematurity (ROP)

A proliferative disease of the retina in small premature babies that involves abnormal vessels and glial tissue, ROP can lead to blindness through scarring and tractional retinal detachment. In such rare advanced untreated cases, ROP can be the cause of leukocoria in smaller eyes. The growing incidence of this condition parallels the improving survival rate for low-birth-weight infants. Eighty percent of cases of ROP resolve alone. New, early, aggressive detection and treatment protocols are designed to prevent scarring and preserve vision.

Rhabdomyosarcoma

A very aggressive malignancy of embryonal muscle tissue found in the orbit. It must be differentiated from orbital cellulitis (see earlier definition). Rhabdomyosarcoma manifests as an acute red swollen eye. It is curable with irradiation and chemotherapy, which preserve vision in 80% of cases.

Strabismus

Any deviation of the eyes away from their common alignment toward the object of regard. The misalignment can be horizontal, vertical, or torsional. A comitant strabismus measures the same in all positions of gaze and normally excludes a paralytic or myogenic cause for the deviation.

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