Scope and Purpose

This report was conducted for the U.S. Preventive Services Task Force (USPSTF) to update its 2011 recommendation on the topic of screening for amblyopia, its risk factors, and refractive error in children ages 6 months to 5 years. The purpose of this report is to systematically evaluate the current evidence on vision screening and treatment for populations and settings relevant to primary care in the United States. In this report, we summarize the evidence on the benefits and harms of vision screening and treatment and the characteristics of screening tests.

Condition Definition

The most common causes of vision problems in children are amblyopia and its associated risk factors (Table 1), nonamblyopic strabismus, and nonamblyopic refractive error.^1-4 Amblyopia is a neurodevelopmental disorder that arises from abnormal processing of visual images that leads to a functional reduction of visual acuity.⁵ Amblyopia is usually unilateral but can occur in both eyes at once. It results from conditions that interfere with normal binocular vision. Specific conditions associated with amblyopia are anisometropia (a difference in refractive power between the eyes, in which one foveal image is more blurred than the other), strabismus (ocular misalignment, in which each eye does not have the same image on the fovea), and deprivation (caused by the blockage of the visual pathway, often due to cataracts, ptosis, or refractive error due to myopia, hyperopia, and/or astigmatism).^6-10 Appendix A provides definitions for these conditions and other relevant terms used in this report. Strabismic and anisometropic amblyopia can coexist. Strabismus can also inhibit development of normal binocular vision in the absence of amblyopia.¹¹

Table 1

Risk Factors for Amblyopia.

Refractive errors in children are due to myopia (nearsighted), hyperopia (farsighted), and/or astigmatism. For young children, mild hyperopia is normal; normal adult visual acuity (20/20) is typically achieved between the ages of 5 to 7 years.^{12, 13}

Prevalence and Burden

Recent population-based studies of U.S. children younger than age 6 years estimate that the prevalence of amblyopia, strabismus, and anisometropia ranges from 1 to 6 percent.^{4, 14-16} Amblyopia risk factors were identified in 5 percent of preschool-age children from 16 photoscreening programs (>400,000 total participants) in the United States.¹⁷ In children younger than age 3 years, strabismus appears to be the most common cause of amblyopia; in children ages 3 to 6 years, strabismus and anisometropia contribute equally.¹⁸ About 4 percent of children younger than age 6 years have myopia, up to 20 percent have hyperopia, and 5 to 10 percent have astigmatism.^19-21

Vision abnormalities in young children could diminish school performance, function, and quality of life, although the long-term functional effects of vision abnormalities are somewhat uncertain. A study of a 1958 British birth cohort that compared adults with normal vision (N=8,432) and adults with amblyopia (N=429) found no differences in educational, health, or social outcomes at ages in the 30s and 40s. Nevertheless, amblyopia is perhaps the most common cause of monocular visual loss in adults.²² The lifetime risk of vision loss for persons with amblyopia has been estimated at around 1.2 percent or higher; amblyopia may significantly increase the risk of severe visual impairment or blindness in the event of vision loss in the nonamblyopic eye.^{23, 24} Strabismus can result in loss of stereopsis (i.e., depth perception) and psychosocial consequences (e.g., from bullying or from diminished self-esteem).

Risk Factors and Natural History

Risk factors for amblyopia, strabismus, and refractive error include positive family history in a first-degree relative, prematurity or low birth weight, low levels of caregiver education, and maternal substance abuse and/or smoking during pregnancy.^25-30 Younger age is associated with higher rates of astigmatism²⁸ and myopia (within the population ages 6 months to 6 years).^{29, 31} Additional risk factors for amblyopia include deprivation of visual stimuli in infancy and early childhood and lack of health insurance.^{25, 32, 33}

It is highly unlikely that untreated amblyopia will resolve spontaneously.^{32, 34} Although amblyopia is treatable, efficacy decreases as children age, and visual loss can become irreversible.^35-37 Visual impairments left untreated can lead to both short- and long-term physical and psychological problems, including physical and verbal bullying,^{38, 39} depression and anxiety,³⁹ poor visuomotor skills,^{40, 41} low self-esteem,⁴² problems at school and work,^{39, 43} and accidents and injuries.⁴⁴

Rationale for Screening/Screening Strategies

There are generally two rationales for screening for amblyopia, its risk factors, and refractive error in preschool-age children. First, preschool vision screening allows detection and treatment of vision abnormalities during a critical developmental stage. Amblyopia is thought to be most effectively treated early because the visual pathways will not develop appropriately otherwise, and vision loss may become permanent. Normal vision development requires that images seen by both eyes are equally clear and aligned. Amblyopia is caused by risk factors present in early childhood.¹¹ It usually does not occur when amblyopia risk factors develop later (i.e., school age, after age 6 years) because the visual system has already developed.⁴⁵ Second, preschool vision screening allows detection and treatment of vision abnormalities before school entry, allowing for optimal school performance and development and potentially minimizing psychosocial consequences.

A variety of screening tools are available to evaluate ocular alignment, visual acuity, and stereoacuity (Table 2). Ocular alignment testing (i.e., strabismus testing) evaluates for alignment-related amblyopia etiologies. Visual acuity testing screens for refractive error and visual deficits associated with amblyopia, such as cataracts. Tests of stereoacuity assess depth perception, the absence of which may suggest underlying amblyopia. These screening tools can be used in isolation or together to evaluate children's vision.

Table 2

Screening Tests for Visual Impairment Used in or Available in Primary Care Settings.

Photoscreening devices use optical images (photographs) of the eye's red reflex to identify risk factors in both eyes simultaneously. Most photoscreeners can estimate refractive error, media opacity, and ocular alignment.⁴⁶ Interpretation of the image is subjective and based on pre-established pass/fail criteria; older devices require a trained interpreter, but newer machines often include computerized interpretation or relay information to a central reading system. Image acquisition takes a few seconds and captures both eyes at once, making them especially useful for preverbal or developmentally delayed children and children who are unable to tolerate longer examinations.⁴⁶

Autorefractors are computerized instruments that provide objective refractive status by measuring how light changes as it enters and reflects off the back of the eye. For patients with reduced visual acuity, it determines the lens power required to accurately focus light on the retina. Advantages of autorefractors include ease and time of use, ready availability, and patient tolerance. Handheld autorefractors require only a few seconds of a child's attention, potentially increasing testability rates versus traditional tabletop models, especially among young children.⁴⁷ A disadvantage of autorefraction is that it typically measures one eye at a time, limiting its ability to detect strabismus without refractive error.⁴⁶

Treatment Approaches

A mainstay of treatment is correction of refractive error, either with eyeglasses or contact lenses. If anisometropic amblyopia persists after a trial of refractive correction, occlusion therapy is the preferred management.^{37, 48, 49} Occlusion therapy consists of covering the nonamblyogenic eye with a traditional eye patch, atropine 1 percent eye drops to blur near vision, or optical penalization (placing a Bangerter occlusion foil over eyeglass lens).^{50, 51} Poor visual acuity not related to amblyopia is often due to refractive error, which includes myopia, hyperopia, and/or astigmatism. Refractive error can be easily and immediately treated with corrective lenses, either eyeglasses or contact lenses, in children as young as 1 week old.⁵¹

Vision therapy (i.e., using eye exercises) is used by some practitioners to treat a variety of eye conditions.^{52, 53} It has been used alone or in combination with occlusion and/or correction of refractive error.⁵⁴ Vision therapy can consist of near-vision tasks (such as tracing or threading beads), binocular therapy, ocular motility training, accommodative therapy, and fixation training.⁵⁵ It may involve the use of lenses, prisms, filters, occluders, specialized instruments, and computer programs, and typically lasts for at least several months.⁵²

Surgical interventions may be required for some causes of amblyopia. Refractory strabismus due to poor ocular alignment can be treated with surgery; the length or location of the extraocular muscles is adjusted to improve the alignment of the eye (but this does not necessarily improve amblyopia or visual acuity).⁵¹ If occlusive pathology is present, this must also be corrected surgically, such as with cataract removal or ptosis correction, in which the levator muscle is tightened, causing the eyelid to elevate so it is symmetric with the other eyelid and allowing a full field of vision.

Current Clinical Practice in the United States

Preschool vision screening is routinely offered in primary care settings. However, estimates of preschool vision screening rates vary by age, location, and other population characteristics. Rates of screening at age 3 years are generally around 40 percent,^56-59 though an analysis of Alabama well-child visits found that only 12 percent of 3-year-olds were screened for vision problems.⁶⁰ Rates of screening generally increase with the child's age. In a survey of pediatricians, 84 percent reported beginning screening before age 5 years (34% began at age 3 years), and 3 percent began screening at 6 months.⁶¹ These rates appear to remain relatively unchanged since older surveys of pediatricians and family physicians.^{59, 62} Caregiver reports of screening rates are roughly similar in the 2009–2010 Medical Expenditure Panel Survey.⁶³ In the same data, rates of screening varied by race/ethnicity and family income. Hispanic children were less likely than non-Hispanic children to have reported vision screening; children whose families earned 200 percent or more above the federal poverty level were more likely to have reported vision screening than those whose families had lower incomes.⁶³ In 2010, the U.S. Department of Health and Human Services reported that 60 percent of children covered by Medicaid in nine states did not receive a vision screening.⁶⁴

Typical components of screening include tests of ocular alignment, visual acuity, and stereoacuity. Measures of visual acuity are generally reported as Snellen (e.g., 20/20, 20/25, 20/30, 20/40, and 20/50) or logarithm of the minimum angle of resolution (logMAR) scales (e.g., 0.00, 0.09, 0.18, 0.30, and 0.40, respectively). In the United States, primary care practices vary in the specific screening tests used, who performs the screening, and screening frequency.⁵⁰ The most commonly used screening tests in primary care settings are visual acuity testing with charts (e.g., LEA Symbols, HOTV) and ocular alignment testing with the cover-uncover test.⁶⁵

Few recent estimates exist for the use of autorefractors and photoscreeners in clinical practice. In two surveys, fewer than 10 percent of pediatricians reported using autorefraction and/or photoscreening.^{59, 61} However, at a single multispecialty group practice, the introduction of a photoscreener increased the rate of screening among 3-year-olds from 10 to 80 percent.⁶⁶ Use has likely increased in recent years because major clinical practice guidelines now recommend photoscreening and handheld autorefraction as alternatives to other forms of screening for children age 6 months or older; some mass community-based screening programs have implemented their use.⁶³ Children who fail vision screening tests are typically referred for a complete ophthalmological examination.

Several guidelines have been issued related to screening children for amblyopia, its risk factors, and refractive error (Appendix A). Briefly, the American Academy of Family Physicians recommends vision screening for all children at least once between the ages of 3 and 5 years to detect the presence of amblyopia or its risk factors; it concluded that the current evidence is insufficient to assess the balance of benefits and harms of vision screening for children younger than age 3 years. In a joint statement, the American Academy of Pediatrics, the American Association for Pediatric Ophthalmology and Strabismus, the American Academy of Ophthalmology, and the American Academy of Certified Orthoptists recommend that vision screening should be performed at an early age and at regular intervals with age-appropriate, valid methods. For children ages 6 months to 3 years, they recommend overall vision assessment with physical examination tests (fixation and follow response, red reflex test, external inspection via direct observation, pupil examination using a flashlight), with the addition of instrument-based vision screening (autorefraction, photoscreening), when available, for children ages 1 to 3 years. They recommend that visual acuity screening may be attempted at age 3 years using HOTV or LEA Symbols. For children ages 4 to 5 years, they recommend visual acuity screening using HOTV or LEA Symbols, cross cover test, and red reflex test. The Canadian Task Force on Preventive Health Care states that there is fair evidence to include testing of visual acuity in the periodic health examination of preschool-age children.

Previous USPSTF Recommendation

In 2011 the USPSTF recommended that all children be screened to detect amblyopia or its risk factors at least once between the ages of 3 to 5 years (B recommendation). The USPSTF concluded that the evidence was insufficient to assess the balance of benefits and harms of vision screening for children younger than age 3 years (I statement).