Ophthalmic screening in children is the essential initial step in protecting against vision loss. Beginning in the newborn nursery and continuing throughout childhood, the pediatrician plays an important role in detecting signs of eye abnormalities.1 The elements of a screening exam vary with the child’s age and are readily incorporated into a pediatric office visit. Recent advances in knowledge and technology allow more accurate and efficient screening. This article describes the primary targeted conditions of pediatric vision screening in children through the preschool years, the rationale for screening, and specific screening techniques.
The Case for Children’s Vision Screening
Many eye diseases of early childhood are unapparent without screening tests. In contrast to adults experiencing vision loss, young children with unilateral and often significant bilateral vision loss tend not to complain, rarely mentioning that their vision is poor. Without screening, their conditions often go undetected. For the conditions targeted by pediatric vision screening, earlier detection leads to better outcomes.
Much of the recent literature relates to screening preschool-aged children for signs of amblyopia. However, an appropriately more comprehensive view of pediatric eye screening also includes testing at earlier ages for infantile cataracts and retinoblastoma. In the process of screening for these targeted conditions, signs of other eye abnormalities may also be detected.
Vision screening for amblyopia is recommended as a component of the well-child examination by organizations, including the American Academy of Pediatrics (AAP), the American Academy of Ophthalmology (AAO), and the US Department of Health and Human Services (HHS).1,2 Currently, in the United States, however, many children fail to receive timely screening examinations.3 Involvement of practitioner and parent is essential for screening rates to improve.
Targeted Conditions and Their Detection
In the first years, the primary targets for screening are cataract and retinoblastoma.4 Although the combined incidence of retinoblastoma and infantile cataract is low, the consequences of missing these diagnoses are serious. Screening for cataract and retinoblastoma is dependent on the pediatrician. Entering the preschool years, the primary screening target becomes amblyopia along with its causative ocular conditions, strabismus and anisometropia.
Retinoblastoma is the most common malignant intraocular tumor of childhood, and the seventh most common pediatric malignancy.5 Most cases are diagnosed by 3 years. Fewer than 25% of cases present with a family history of retinoblastoma. The primary screening test for retinoblastoma is to look for a red reflex in each eye. An abnormal, whitish, pupillary reflex color is termed leukocoria. Because retinoblastoma and many cataracts develop later in infancy, the red reflex should be re-evaluated at each well-child visit, rather than only in the newborn nursery.
After leukocoria, the second most common presenting sign of retinoblastoma is strabismus; therefore, every child with strabismus should be checked carefully for the presence of a red reflex in each eye.
It may be reasonable to defer ophthalmology referral of a 2-month-old child with intermittent strabismus for a few months but only after the presence of a red reflex has been confirmed. Unfortunately, many children with retinoblastoma or infantile cataract experience delays in detection or referral for ophthalmologic evaluation.5,6,7 Often, leukocoria is initially observed by a family member or friend.5 When retinoblastoma is first detected by a pediatrician’s red reflex test rather than by later observations by the child’s family, there may be a greater chance of preserving the eye.7
Occasionally, these white or yellow pupils are noted in photographs. Not recognizing their significance, parents may delay telling their pediatrician that leukocoria has been seen. Similarly, some pediatricians delay referral of these seemingly asymptomatic children to an ophthalmologist.6 Mortality from retinoblastoma is related to the extent of disease and is, therefore, dependent on the tumor stage at diagnosis.
The prognosis for preserving the eye and preserving useful vision is also related to the extent of disease. With the recent successes of intra-arterial chemotherapy, chemoreduction, and focal treatment with laser or cryotherapy, there are now several modalities available for treating many retinoblastomas without enucleation.8,9
Although usually recognized as a condition of the elderly, cataracts may be congenital or develop during infancy. The incidence of infantile cataracts is estimated at between one and six per 10,000 live births.10 Treatment of an infantile cataract involves surgery followed by postoperative optical correction with glasses, a contact lens, or an intraocular lens implant (IOL). Timing of treatment is critical because cataracts rapidly cause severe amblyopia. Excellent vision results may be achieved with treatment of cataracts in the first few weeks of life.11–13
Surgery for infantile cataract has a high success rate, but persistent vision loss often results from late diagnosis and visual deprivation amblyopia.11 A good visual outcome is, therefore, often dependent on the pediatrician’s detection of leukocoria in early infancy.
Amblyopia is a form of vision loss caused by deficient visual stimulation of an eye, and occasionally both eyes, during the years of visual development. The potential for developing amblyopia exists through the preschool years.
Several ocular conditions may interfere with normal development of vision, leading to amblyopia. Although amblyopia is caused by ocular conditions, the defect of amblyopia develops within the visual centers of the brain.14 With time, untreated amblyopia leads to permanent vision loss.15 Amblyopia is most commonly caused by strabismus.
Anisometropia, a difference in refractive power between the two eyes, causes amblyopia without any noticeable abnormality in a child’s outward appearance. Visual deprivation, from a cataract, for instance, may cause severe amblyopia. Amblyopia may be directly screened for with visual acuity testing or by objective tests for amblyopia risk factors, such as anisometropia, high refractive errors and strabismus.
Amblyopia is certainly common, with roughly one amblyopic child per kindergarten class. Studies estimate the prevalence of amblyopia at 1% to 5%, with a possibly higher prevalence among white children.16–18
Strabismus is the condition of ocular misalignment. In strabismus, the visual axes of the two eyes are not directed simultaneously toward the same object. Strabismus is classified by the direction of the deviating eye, as in esotropia, exotropia, and hypertropia. Subtle expressions of strabismus are often diagnosed later than more obvious cases, and, therefore, the angle of strabismic deviation inversely correlates with the density of amblyopia.19 The corneal light reflex test, the cover test, and the Brückner test are used to detect strabismus.
Although successfully treated when detected in the preschool years, amblyopia is the leading cause of monocular vision loss within America’s pre-retirement adult population.20,21 Delay in treatment leads to worsened visual outcomes.15 Uncorrected amblyopia may harm school performance, occupational level, and adult self-image.19,22 Presence of amblyopia places the opposite eye at increased risk for vision loss.19,23
The prevalence of amblyopia in the general population may be significantly reduced by screening for amblyopia by 4 years.24–26
Amblyopia treatment outcomes are better with early detection and treatment.26–29 Recent studies have suggested that very early detection of amblyopiainducing factors by photoscreening further improves outcomes.26,29 Compared with other medical interventions, the cost of identifying and treating amblyopia is low, and successful treatment results in decades of improved vision.30,31
The high prevalence of amblyopia in today’s adult population is likely caused by the previous generation’s incomplete vision screening success and difficulties with treatment compliance. Today, unfortunately, these factors have not been eliminated. An HHS 2002 National Health Interview Survey found that only 36% of children younger than 6 years had ever undergone vision testing.3 Charity-based preschool screening programs in the United States report even lower penetrance of 10% and 14% in selected statewide screening programs.32
Because of problems with referral and children appearing for appointments, not every child who fails a screening receives a comprehensive eye exam.33 By increasing the number of children reached, medical home-based preschool vision screening, combined with timely referrals of screening failures, holds the potential for significantly reducing the incidence of permanent vision loss from amblyopia.
Children’s Screening Tests
When to Screen
The appropriate screening tests to be performed are dependent primarily on the child’s age.1 In the newborn nursery and at each well-child exam until the child reads an eye chart, red reflex testing should be performed. The external appearance of the eyes and eyelids is also inspected. From 3 months to 5 years, corneal light reflex testing is performed. Corneal light reflex testing may be combined with red reflex testing in the Brückner test, described below.
An assessment of fixation and following behavior is performed beginning at 2 to 3 months. From 6 months to 5 years, cover testing is performed. From 4 to 5 years, preliterate eye chart testing is performed. Earlier eye chart testing may be attempted at 3 years but is more time-consuming and less reliable.
In response to difficulties in eye chart screening, particularly in children 3 years and younger, newer screening technology has evolved. Photorefraction devices, such as PediaVision and the SureSight Vision Screener, are designed to detect abnormalities of ocular refractive power and/or binocular alignment that are precursors of amblyopia.
This eye examination strategy is intended for use in apparently normal children without any condition or family history placing them at increased risk for eye disease. Other recommendations apply for certain children at greater risk for eye disorders.
For example, the AAP recommends an ophthalmology referral for all children with Down syndrome by 6 months.34 Because of an increased risk of strabismus, amblyopia, and refractive errors, children born prematurely should undergo follow-up ophthalmologic examinations, even after complete resolution of retinopathy of prematurity.35 A family history of conditions, such as retinoblastoma and congenital cataract, should also prompt ophthalmology referral.
Red Reflex Test
The red reflex is produced by light reflecting from the retina. Anything obstructing a view of the retina, such as a cataract, will block the red reflex. Certain abnormalities of the retina, notably retinoblastoma, may also eliminate or distort the red reflex (see Figure 1, page 78). Red reflex testing is straightforward and quick. Checking the red reflexes of all preverbal children is manageable in even the busiest practice. To perform the test, a direct ophthalmoscope is used to view each pupil 12 to 18 inches from the child. If a cataract is present, the red reflex may be absent, dulled or patchy. Alternatively, the pupil may appear white or yellow. An eye harboring a retinoblastoma may have a white or a shiny “cat’s eye” pupillary reflex.
Figure 1. Leukocoria Caused by a Right Eye Retinoblastoma. (Figures Courtesy Robert W. Hered, MD.)
Importantly, even a partially obscured red reflex may be due to significant disease; if the red reflex of one eye is present but dimmer or of a different hue than its pair, then a prompt ophthalmology referral is indicated (see Figure 2, page 78).
Figure 2. Congenital Cataract. This Zonular Cataract Partially Obscures the Red Reflex.
External Inspection of the Eyes
In addition to looking for the red reflex in an infant, the external appearance of the eyes and eyelids should be observed. Eyelid ptosis may cause amblyopia or be a sign of a neurologic abnormality. Small and large corneas are associated with eye disease. A large cornea may be due to infantile glaucoma. Asymmetry of pupil size (anisocoria) may be the result of eye disease or a neurologic abnormality.
Fixation Behavior Assessment
While performing eye tests on preverbal children, assessing the child’s fixation behavior is also recommended to qualitatively assess a young child’s vision. Visual behavior in infancy evolves rapidly. By 6 weeks, the child should make some visual response to your face. By 2 months, there should be some following behavior demonstrated. If poor fixation and following is noted binocularly after 3 months, an ophthalmology consultation is recommended.
By 4 to 6 months, fixation behavior may be tested monocularly, with each eye alternately covered. If poor fixation and following occurs with one eye occluded, or if the child strongly protests one of the eyes being occluded, the uncovered eye may have poor vision. Also, the presence of nystagmus at any age is reason for ophthalmology consultation.
Corneal Light Reflex Test
The smooth convex surface of the cornea causes a sharp reflection from any point source of light, such as a penlight or direct ophthalmoscope. The position of this light reflex, relative to the underlying iris and pupil, is dependent on the alignment of the eye.
To perform the corneal light reflex test, one directs a light on the child’s eyes and observes the corneal light reflexes of both eyes simultaneously. A temporal location of the light suggests esotropia, an inward misalignment of the eye. A nasal location of the light reflex suggests exotropia, an outward misalignment of the eye (see Figure 3, page 79).
Figure 3. Corneal Light Reflex Test for Assessing Strabismus. A. Esotropia Is Demonstrated by the Temporal Location of the Left Corneal Light Reflex. B. Exotropia Is Demonstrated by the Nasal Location of the Left Corneal Light Reflex. C. Normal Position of the Corneal Light Reflexes in Pseudoesotropia.
The Brückner Test
The Brückner test is a combined, simultaneous corneal light reflex and red reflex test, performed with the direct ophthalmoscope. The Brückner test may reveal strabismus, anisometropia, leukocoria, or anisocoria. A direct ophthalmoscope is held 2 to 3 feet from the child. The red reflexes and the corneal light reflexes of both eyes are viewed simultaneously. Interpretation of the corneal light reflex is the same as with the standard corneal light reflex test. As with other red reflex testing, an abnormal red reflex in the Brückner test may indicate cataract or retinoblastoma.
In addition, a brighter red reflex in one eye may indicate that the eye is strabismic. A difference in red reflex color may also indicate anisometropia, a difference in optical power between the eyes and a risk factor for amblyopia (see Figure 4). Any abnormality of corneal light reflexes, red reflex symmetry, or pupil symmetry found on Brückner test should prompt an ophthalmology referral.1
Figure 4. Brückner Test. Asymmetry of Red Reflexes Caused by Anisometropia.
Cover tests are used to assess eye alignment and diagnose strabismus. In the cover test, each eye is alternately occluded and any resultant eye movement of the opposite non-occluded eye is observed. Such a refixation movement may indicate the presence of strabismus.
Preliterate Eye Charts
The primary goal of eye chart screening in the preschool age is to detect amblyopia. Preliterate eye charts are available for screening children not yet ready for screening with letters. While screening for amblyopia, myopia, astigmatism, and vision loss from other causes may be revealed.
Current AAP guidelines recommend using an eye chart by 3 years and retesting within 6 months if the child is considered untestable. Screening with eye charts is difficult at 3 years; higher testability rates, reduced time to test, and improved validity of results are achieved at 4 years. Barriers to preschool screening reported by pediatricians include lack of cooperation by children, screening being too time-consuming, and lack of training. By using age-appropriate charts and emphasizing eye chart screening at 4 years, testing time, testability, and reliability may be improved.36
The HOTV chart and the Lea Symbols chart are good options for screening 3- and 4-year-old children (see Figure 5). Testability is improved by testing children at 10 feet from the eye chart rather than 20 feet. Children considered untestable are more likely to have an underlying vision problem and consideration should be given for referral.37
Figure 5. The Lea Symbols Chart Is a Good Option for Screening 3- and 4-Year-Old Children.
When screening with eye charts, it is important to ensure that each eye is tested separately. It is common for amblyopic children to attempt peeking at the chart with the better-seeing eye. Rather than holding an occluder in front of an eye, it is recommended that the opposite eye be patched. To improve the sensitivity of amblyopia detection, whole rows of symbols or letters should be presented at once, rather than presenting individual symbols. Alternatively, charts with crowding bars around each symbol help to preserve the test’s sensitivity if presenting only one symbol at a time.
To pass the screening, 3- and 4-yearold children must correctly identify the majority of symbols on the 20/40 line of the chart. For 5-year-old children, the critical line may be advanced to 20/32. If either eye does not reach this acuity level, the patient is referred for further evaluation. For efficiency in screening, testing vision only to the critical passing line will save time compared with attempting to fully test each child to the 20/20 line of the chart.
Autorefraction and Photoscreening
In response to difficulties in eye chart screening, particularly in children 4 years and younger, objective screening technology has been developed. Photoscreening devices, such as the PediaVision device, use optical images of the eye’s red reflex to estimate refractive error, media opacity, and ocular alignment.
Autorefraction directly measures the refractive error of each eye. Portable handheld autorefractors, such as the SureSight Vision Screener, are useful for detecting high refractive errors and anisometropia, which are risk factors for amblyopia.
The technology of photoscreening and autorefraction devices has improved over the past few years and now typically delivers instant and reliable measures of amblyopia-producing conditions. These devices offer the advantage of objective testing that requires minimal patient cooperation. The Vision in Preschoolers Study (VIP) found that in the hands of eye care professionals, certain objective screening devices were comparable in accuracy to the Lea Symbols eye chart.38 Other recent studies have shown success with photoscreening devices in mass preschool screening programs.39–41