Eye disorders in childhood

J. E. Elder

A systematic approach to children’s eye disease allows rapid determination of the correct diagnosis or initiation of appropriate further investigation.

Visual development

A rapid sequence of anatomical and functional changes in the visual apparatus enables vision to develop from a very low level after birth to near adult levels by 12–18 months of age. At birth an infant has visual acuity of approximately 6/120 and by 12 months this has improved to about 6/12. This rapid development is the result of retinal maturation, myelination of the visual pathways, the ability to accommodate (change the focal length of the eye) and maturation within the visual cortex. The first three of these processes (retinal maturation, myelination and accommodation) are complete by 4–6 months of age. The maturation of the visual cortex occurs more gradually, over a 6–8-year period, with the most rapid phase being in the first 2 years. Anything that interferes with this gradual cortical maturation may result in the development of amblyopia, which is one of the commonest ophthalmic abnormalities of childhood (see Amblyopia, below).

Measurement of vision in children

Measurement of visual acuity in preverbal children presents a challenge. Asking the parent ‘Does your child see well?’ or ‘How well do you think your child sees?’ often gives useful information about an infant’s visual function. If a parent expresses concern about an infant’s vision, take note, as this concern is often well founded.

An understanding of normal visual behaviour is vital to estimating visual function in infancy. At birth, when alert, an infant should be able to fix on a face briefly. By 6 weeks of age most infants smile in a visually responsive fashion to a face. At this age the infant will also be able to follow a face or light through an arc of 90°. By 6 months of age an infant can reach for a small object and can actively follow objects in the visual environment. At 12 months of age a child should be able to reach and pick up tiny objects such as hundreds-and-thousands (‘sprinkles’).

More formal assessment of visual acuity becomes possible with the development of language. Children with specific language delay or more general intellectual delay will have difficulty with these tests of visual acuity. Picture-naming tests can be done by children between 2 and 3 years of age. Single letter-matching tests are within the abilities of most 3–4-year-olds. The standard Snellen chart test is often not performed well until the child is between 5 and 6 years of age. The vision should be tested for each eye individually. As with all testing in children, patience and an encouraging manner are vital to obtain the best results. Repeat the test on another occasion if the test results seem inaccurate.

The notation for documenting visual acuity is the Snellen fraction, e.g. 6/6. Most visual acuity tests use standard distances of 3 or 6  m between subject and chart. The numerator of the Snellen fraction is the distance from the chart while the denominator indicates which line on the chart was the smallest to be seen. If the vision is poor the subject should be brought closer to the chart. The vision then may be recorded as 2/18 or 1/60, etc., depending on how close the subject is to the chart and which line is read.

What level of vision is abnormal? (or, when to refer!)

This depends on the age of the child. An infant who is not fixing and following by 3–4 months, or reaching for small objects and tracking objects in the visual environment by 8–12 months, deserves further examination and investigation.

If the child is able to do a more formal test of acuity, a difference between the two eyes of two or more lines (that is 6/6 and 6/12) indicates the need for further assessment. In children less than 3 years of age vision of 6/18 or less in either eye should prompt referral and in children older than 3 years 6/12 is an acceptable cut-off for referral.

Assessment of a child with a possible eye problem

History

Prematurity, perinatal difficulties (e.g. birth asphyxia), significant syndromes (e.g. Down syndrome) and other sensory impairment (e.g. deafness) are associated with an increased risk of eye disease. Developmental delay often interferes with assessment of visual acuity, especially if language or intellect is affected. Common childhood eye problems such as strabismus and refractive errors have a clearly identified familial tendency, although the precise genetics are not well understood. Finally, the parents’ perception of a child’s visual function is important, particularly if there is concern that the vision is poor.

In keeping with paediatrics in general, observation without approaching or touching a child often supplies a great deal of information. By observation it is possible to rapidly determine an infant’s use of vision. Does the child smile at a face? Is the child looking around the room? If something moves, does the child look to it? If there is a noise, does the child look to the source of the noise? A blind child will become still and will often drop the head down while using hearing to further localize the source of the sound, but will not look towards this source.

Most eyelid, eyelash and ocular surface abnormalities can be detected readily by simple observation. Many intraocular abnormalities can be detected by examination of the ‘red reflex’. This is the red to orange colour seen within the pupil when the line of illumination and observation are approximately coaxial (that is, the same). This situation is most easily obtained by observing the child’s eye with a direct ophthalmoscope from a distance of about 1  m. It is then easy to compare the reflexes for the two eyes and the child is not threatened by the examiner getting too close. A dull or absent red reflex indicates an opacity, such as a cataract, in the normally clear media of the eye. A white reflex results from an abnormally pale reflecting surface within the eye, such as a white retinal tumour (retinoblastoma). While these intraocular disorders are rare, they are important in terms of the severe effect on vision or threat to life.

Misalignment of the eyes

Strabismus or squint is common in childhood and accurate assessment to confirm or refute the presence of misalignment is an important skill for anyone who deals with children.

Observation will confirm the presence of large-angle strabismus. However, a broad nasal bridge or prominent epicanthic folds will mimic milder degrees of strabismus, especially in younger infants. This situation is known as pseudostrabismus (Fig. 22.2.1). The epicanthic folds cover the sclera on the medial aspect of the globe while the lateral sclera is easily visible. This creates the appearance of misalignment, particularly when the child looks laterally. Examining the symmetry of corneal light reflections will help to avoid being misled by pseudostrabismus.

The cover test is by far the most reliable method of detecting strabismus. The cover test is done by first getting the child to fix on an object while the observer determines which eye appears to be misaligned. The eye that appears to be fixing on the object (and not misaligned) is then covered while the apparently misaligned eye is observed. If strabismus is present a corrective movement of the misaligned eye will be seen as this eye takes up fixation on the object of regard (Fig. 22.2.2). If no movement is seen then the eye is uncovered.

The cover test is then repeated but the other eye is covered this time and the eye that is not covered is again observed for a corrective movement and, if present, strabismus is confirmed. The test can be repeated as many times as necessary. If no movement is seen following repeated covering of either eye, then no strabismus is present. Care must be taken to let the child fix with both eyes open before covering either eye, otherwise normal binocular control may be prevented and a small latent squint (phoria) may be detected. Latent squints are normal variants and are of no significance.

Common eye problems in childhood

Amblyopia

Amblyopia is the cortical response to abnormal input from the eyes and is manifest as reduced visual acuity in one or both eyes. This abnormal input may result from a refractive (spectacle) error, a structural abnormality of the eye (e.g. cataract) or strabismus. Provided it is detected early enough, while the developing visual cortex is immature, amblyopia is treatable. Conversely, if the amblyopia is not treated before visual cortex maturation (about 7 years of age), it may not be reversible later in life. Detection of amblyopia is one of the major reasons for routine visual screening in childhood.

Common causes of amblyopia are strabismus and refractive errors. Refractive errors cause a poorly focused image to form on the retina and thus a poor-quality image to be transmitted to the cortex. Such input does not stimulate normal cortical development and amblyopia results. Strabismic (misaligned) eyes are not necessarily out of focus; however, if the cortex ‘paid attention’ to the image from each eye diplopia would result, as each eye is sending a different view of the world. In children, the immature visual cortex is capable of ignoring the image from one eye. If this situation is allowed to persist the cortex may completely ignore or suppress the input from a deviating eye and amblyopia will result.

Treatment of amblyopia involves correcting any focusing errors with appropriate spectacles and forcing the brain to use the amblyopic eye by depriving the brain of clear input from the better-seeing eye, most commonly with a patch. Unfortunately, simply realigning strabismic eyes is not enough to overcome amblyopia secondary to strabismus.

Strabismus

A squint or misaligned eye is important to detect as it is frequently associated with amblyopia. Most childhood strabismus is the result of failure of binocular control at a cortical level within the central nervous system (CNS). Less commonly it is the result of cranial nerve lesions or extraocular muscle disease. In most children this CNS abnormality in eye movement control is an isolated abnormality with no other associated neurological or intellectual problems. However, children with widespread CNS abnormalities have an increased risk of developing strabismus. Down syndrome is a good example of this, with an approximately tenfold increase in the risk of developing strabismus.

The diagnosis of strabismus is outlined above and detailed consideration of the therapy of strabismus is beyond the scope of this chapter. The following is a brief description of the commoner patterns of strabismus seen in childhood and an outline of management.

Infantile esotropia

This is a large-angle convergent squint seen before 6 months of age. Strabismic amblyopia is common in infantile esotropia but refractive errors are rare. Patching followed by surgery is the most common initial treatment. Children with infantile esotropia need to be followed up throughout childhood, as about one-third need more than one operation and amblyopia can occur following apparently successful initial treatment.

Intermittent divergent strabismus

This occurs from 18 months of age onwards. It is often more noticeable on distance fixation and may be associated with closure of the deviating eye, especially in bright light. Amblyopia is uncommon, as the deviation is intermittent and presumably when the eyes are straight normal visual development proceeds. In some cases the divergence becomes more constant and in such situations surgery may be undertaken to improve alignment.

Accommodative esotropia

This occurs in children who are excessively long-sighted (hypermetropic). To overcome hypermetropia and focus a clear image on the retina, accommodative effort is used. Accommodation consists of the combination of changing focal length of the lens and converging the eyes (so that both are directed at the nearer object of regard). Thus in children with excessive hypermetropia there is increased focusing and at times excessive convergence; that is, a convergent squint (esotropia) appears as a result of the increased accommodative effort used by these children. Accommodative esotropia can be completely or partially corrected by prescribing glasses that compensate for the appropriate amount of hypermetropia. Amblyopia is often seen in association with accommodative esotropia and requires treatment. If glasses only partly correct the esotropia, surgery may be indicated to obtain optimal alignment.

A 3-year-old girl presented with a history of a worsening inward turn of her left eye over four months. The cover test confirmed a left convergent squint and the red reflex was normal in each eye. Subsequent assessment by an ophthalmologist confirmed the findings and her visual acuities were 3/3 in the right eye and 3/9 in the left with refraction showing she was long-sighted. When next seen 6 months later she was wearing glasses and had been patching her right eye 2 hours a day. Her eyes were straight to cover test and her parents reported that her left vision was slowly improving and that surgery was not going to be required in her case.

Refractive problems are the result of defects in the focusing components of the eye. These defects include abnormality of corneal curvature (a frequent cause of astigmatism) and abnormalities of lens power and axial length of the eye (which may result in hypermetropia or myopia – short-sightedness). Children will rarely complain of poor vision related to refractive error. Rather, they readily accept the vision they have and get on with life. Children with high myopia will often manifest myopic behaviour (they will go very close to objects to look at them). Different refraction in either eye will often result in amblyopia because one eye will generally have a clearer image than the other and thus enable better cortical development for that eye.

Routine screening of visual acuity is the only reliable way of detecting the majority of refractive errors in children. In many countries there are both preschool and school entry tests of visual acuity for this reason. Such screening testing needs to be reliable, available to all of the target population and followed up with appropriate intervention when defects are identified. As cortical maturation of vision occurs at about 7 years of age, screening should ideally commence in 3–4-year-olds, before any amblyopia becomes difficult to reverse.

If a refractive error is suspected in a young child because of strabismus or poor visual acuity, then accurate and objective testing with cycloplegic retinoscopy is required. If a child is prescribed glasses, these should be worn the majority of the time.

• The parents’ assessment of their infant child’s vision is often very accurate; if they are concerned their child is not seeing you should be concerned also

• Always try to gain as much information as possible by observation before actively engaging a child in an examination. Red reflexes can be observed from a distance. Urgent referral is required if an abnormal red reflex is found

• Children under 7 years of age will rarely complain of visual difficulty relating to refractive errors (reduced visual acuity). A vision screening programme is the most reliable method of detecting reduced visual acuity in children of this age

• Strabismus is a common cause of amblyopia. All suspected or confirmed strabismus should be referred to an ophthalmologist for further assessment and management

• Cover testing is the most accurate clinical method of diagnosing strabismus. When doing a cover test always make sure that the child is looking at a interesting fixation target – a small toy is useful for near fixation and a picture or larger toy for distance fixation

• Amblyopia is generally reversible if it is detected early and appropriate management is initiated
Watery and sticky eyes

This occurs commonly in infancy as the result of congenital nasolacrimal duct obstruction. About 10% of newborn infants have obstructed nasolacrimal ducts. This will present as a watery and sticky eye in the first few weeks of life. Despite the persistent discharge the eye is generally not red or inflamed. An inflamed eye suggests an alternative diagnosis such as infective conjunctivitis. If the obstruction persists, the lower lid will often become red and sometimes slightly scaly as a result of the skin being constantly moist.

The differential diagnosis includes trauma, conjunctivitis and infantile glaucoma. These conditions are all described below.

Most congenital nasolacrimal duct obstructions resolve spontaneously. Approximately 95% of cases have resolved by the time of the first birthday, with most doing so in the first 6 months. In persistent cases, probing under a general anaesthetic is recommended after 1 year of age.

Trauma

Trauma to the eye can take many forms. Physical trauma to the eye and surrounding structures may be blunt or sharp. Trauma can also result from radiation (thermal and electromagnetic) and chemical agents.

Sharp trauma may be due to a range of causes, from tiny objects such as a subtarsal foreign body causing a corneal abrasion, to fingernail scratches through to penetration of the eye by sharp objects such as a scissors blade or dart. Surface trauma can be diagnosed easily with the help of fluorescein staining and a cobalt blue light. Areas of epithelial abrasion will fluoresce green. If a round ulcer and/or vertical linear abrasions are seen, suspect a subtarsal foreign body and the upper lid should be everted. If identified, most subtarsal foreign bodies can be removed with a moistened cotton bud. Superficial trauma is treated with antibiotic ointment and a patch and daily review until any epithelial defect (ulcer or abrasion) is healed.

If the wall of the eye (cornea or sclera) has been penetrated, intraocular contents may prolapse out through the wound, the iris and pupil may appear distorted or the anterior chamber may be shallower than normal. Any suspected penetration of the eye must be referred to an ophthalmologist for further investigation and management. The eye should be protected with a cone that does not exert any pressure on the eye. If vomiting is likely or occurs an anti-emetic should be given to prevent further prolapse of intraocular tissue.

Thermal injuries to the eye itself are rare, as in most burn situations the eyelids are firmly closed and thus protect the eye. Facial burns may cause scarring that interferes with lid function, leading to exposure and drying of the eye’s surface. If a primary thermal injury to the eye is suspected, fluorescein dye should be used to detect any ulceration. If ulceration is found, treatment is with antibiotic ointment and a patch.

Radiation injuries to the eye are rare in childhood and most are the result of intentional irradiation as part of medical therapy for facial and ocular neoplasia. Typical injuries are cataract, dry eye syndrome, radiation retinopathy and optic neuropathy. These changes are seen some considerable time after the irradiation.

Chemical burns to the eye are unusual in childhood but potentially are very serious, especially if the chemical is alkaline. Many domestic cleaning agents are alkaline. Strong alkali will denature and dissolve protein and penetrate deeply into the surface of the eye. Acids tend to coagulate surface structures and this often prevents deeper penetration of the acidic chemical into the eye. Immediate first aid should consist of copious irrigation with water at the site of the accident and this should be continued for at least 10 minutes. Following adequate irrigation all chemical burns of the eye should be referred to an ophthalmologist.

• Most blocked tear ducts resolve spontaneously by 1 year of age

• Simple inspection with the addition of fluorescein staining will enable the diagnosis of most physical trauma to the eye

• All chemical injuries to the eye should be regarded as serious. Copious irrigation is the cornerstone of immediate management of all chemical injuries to the eye

Conjunctivitis may result from infective, allergic or chemical agents interacting with the conjunctiva. Symptoms are itch, pain and irritation or a gritty sensation. Signs are epiphora (watering), discharge and erythema of conjunctiva and lids. The relative prominence of different symptoms and signs varies with the cause of the conjunctivitis (Table 22.2.1).

Conjunctivitis occurring in the first few weeks of life is generally bacterial and frequently acquired from the birth canal. Neisseria gonorrhoeae and Chlamydia trachomatis both cause a conjunctivitis with copious discharge and marked erythema in the neonatal period, termed ophthalmia neonatorum. Gonococcal conjunctivitis is serious because of the risk of spontaneous perforation of the cornea and resultant loss of vision and also the risk of more generalized sepsis. Chlamydial conjunctivitis is significant because of the risk of more generalized chlamydial sepsis. For accurate and prompt diagnosis of these infections, microbiological diagnosis and systemic as well as topical antibiotic therapy is needed. For culture, conjunctival swabs should be directly inoculated onto culture medium plates and conjunctival scrapings for Gram staining and immunofluorescent staining should be taken.

Bacterial conjunctivitis occurring outside the first few weeks of life in children is usually the result of relatively innocuous organisms (e.g. Staphylococcus spp. and Haemophilus spp.) Microbiological investigation is not usually indicated and a broad-spectrum topical antibiotic should be prescribed (such as neomycin/polymyxin or chloramphenicol). Concern has been raised about topical chloramphenicol preparations because of a perceived risk of secondary agranulocytosis. It is the author’s belief that this risk is extremely low but does exist and should not stop short-term use of topical chloramphenicol.

Viral conjunctivitis is relatively common at all ages and clinically may be very difficult to differentiate from bacterial conjunctivitis. The discharge may be somewhat less with viral conjunctivitis. Viral conjunctivitis is frequently associated with upper respiratory tract infection symptoms. If the aetiology is uncertain, topical antibiotics as for bacterial conjunctivitis should be used.

Allergic conjunctivitis is common in children of all age groups and has itch as its most prominent symptom. House dust mite, grass and other plant pollens are common allergens that precipitate allergic conjunctivitis. Therapy depends on the severity of the symptoms. If mild, cold compresses may be all that is needed. For more severe symptoms soothing topical astringent agents that include a topical antihistamine are helpful. In more persistent and severe cases topical sodium cromoglycate and steroid preparations may be indicated. Topical steroid should be used with the supervision of an ophthalmologist because of the risk of significant side effects, including cataract and glaucoma.

A 4-year-old boy presented with a 12-hour history of a red and watery eye. He complained of pain and his parents had not observed any discharge. Examination revealed a red eye with no obvious trauma or foreign body on the surface of the eye. Fluorescein staining demonstrated a round ulcer on the upper part of the cornea. On everting the upper eyelid a small foreign body was found and was removed with a moistened cotton bud. The ulcer was treated with antibiotic ointment and a pad and healed in 1 day.

These are common in children and most arise in the skin appendages of the eyelids (lash follicles and meibomian glands). Infection of a lash follicle is called a stye (or hordeolum externum) and acute infection of a meibomian gland is known as hordeolum internum. Unless there is significant secondary erythema of the surrounding lid, topical and systemic antibiotics are not indicated. Occasionally, severe preseptal cellulitis will follow a focal lid infection and systemic (often intravenous) antibiotics will then be needed for treatment.

More chronic inflammation of a meibomian gland is known as a chalazion. This is generally the result of sterile chemical inflammation rather than infection and occurs when the contents of a meibomian gland escape into the lid following blockage of the opening of the gland at the lid margin. A chalazion will appear as a lump in the substance of the lid and is often not particularly inflamed in appearance. Topical antibiotics seldom hasten resolution. Warm compresses may give symptomatic relief and help drainage. Chalazia may persist for many months. Some will discharge through the conjunctiva or the skin. On occasions surgical drainage is indicated for a persistently inflamed and large chalazion.
Practical points