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Kemper A, Harris R, Lieu TA, et al. Screening for Visual Impairment in Children Younger than Age 5 Years: A Systematic Evidence Review for the U.S. Preventive Services Task Force [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2004 May. (Systematic Evidence Reviews, No. 27.)

  • This publication is provided for historical reference only and the information may be out of date.

This publication is provided for historical reference only and the information may be out of date.

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Screening for Visual Impairment in Children Younger than Age 5 Years: A Systematic Evidence Review for the U.S. Preventive Services Task Force [Internet].

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Vision Impairment and Screening

Visual impairment in young children is common, affecting 5% to 10% of all preschool children.1 In 1996, the US Preventive Services Task Force (USPSTF) recommended screening all children for amblyopia and strabismus once before entering school, preferably between ages 3 and 4 years of age (“B Recommendation”).1 The USPSTF also recommended that clinicians be alert for signs of ocular misalignment when examining all infants and children. The Canadian Task Force on Preventive Health Care similarly found that fair evidence supports the inclusion of visual acuity tests in preschool-aged children.2

Based on these recommendations and the belief that early detection of visual impairment is important, many professional organizations have released practice guidelines, including the American Academy of Pediatrics (AAP), the American Academy of Family Physicians (AAFP), the American Academy of Ophthalmology (AAO), the American Association of Pediatric Ophthalmology and Strabismus (AAPOS), and the American Optometric Association (AOA).3 Other advocacy groups, such as the nonprofit organization Prevent Blindness America,3 have also developed guidelines. All these guidelines recommend screening children in the preschool years for both visual acuity and stereoacuity. These guidelines also suggest various specific tests for screening.

In 1998, the Maternal and Child Health Bureau (MCHB) of the Health Resources and Services Administration convened an expert panel to evaluate the evidence regarding the effectiveness of screening and to develop a set of harmonized guidelines based on the various available guidelines.4, 5 MCHB has recently funded the AAP to continue the process of developing uniform screening guidelines and to develop strategies to promote vision screening. Although vision screening can occur in a variety of settings, such as schools, this review focuses on screening in the clinic setting.

One major problem with vision screening has been the challenge of evaluating young and sometimes uncooperative children. New screening technologies that allow for testing with only minimal involvement from the child have begun to become commonly available. These new tests may permit early diagnosis of conditions associated with amblyopia and therefore allow for primary prevention of amblyopia. By identifying children with impaired visual acuity, these devices may also enable clinicians to improve vision for this population during the preschool years. These devices were not evaluated when the USPSTF last reviewed this topic.

Despite significant interest in promulgating vision screening guidelines, questions have been raised about the efficacy of vision screening programs. In 1997, a systematic review sponsored by the British National Health Service (NHS) found a lack of high-quality research on the natural history of amblyopia and the efficacy of treatment.6 This led the study's authors to question the value of preschool vision screening. This report met with significant criticisms,7 including assertions that substantial animal data were ignored and that the report excluded retrospective clinical studies. Because clinicians may thus be confused about whether to screen young children routinely, we decided to re-examine vision screening in this age group.

To assist the USPSTF in updating its previous recommendations regarding vision screening in children through 5 years of age, the USPSTF staff at the Research Triangle Institute-University of North Carolina (RTI-UNC) Evidence-Based Practice Center (EPC) conducted a systematic review of high-quality scientific evidence regarding (1) the prevalence of visual disorders in children, (2) the effectiveness of available screening tests, (3) the effectiveness of treatment, and (4) the impact of visual impairment on the individual. Because screening devices that can be used in very young children are now available, we evaluated vision screening separately for children less than 3 years of age and for children 3 through 5 years of age.

We did not address screening for color blindness or screening for disorders that indirectly cause visual impairment, such as retinoblastoma. This report does not address the screening of special populations, such as premature children or children with neuromuscular disorders, who have a high likelihood of having a visual impairment and would benefit from direct referral to an eye care specialist. Similarly, this report does not focus on children with profound visual impairment. This report focuses on amblyopia, conditions related to amblyopia, and refractive errors. Because terms related to these impairments can be complicated, we begin with a background summary of visual impairment and screening strategies.


Types of Vision Impairment. - Amblyopia is reduced visual acuity in one or both eyes due to abnormal binocular interaction. Causes of amblyopia include ptosis, cataracts, strabismus, and unequal refractive errors between the 2 eyes (anisometropia).8 One large series found that strabismus accounted for 48% of the cases of amblyopia, refractive errors for 20% of the cases of amblyopia, and mixed strabismus and refractive errors for 32% of the cases.9 Cataracts and ptosis are rare in children. Primary prevention of amblyopia may be possible by early treatment of those conditions associated with amblyopia.

Amblyopia is associated with visual impairments that present early in life. If the visual impairments associated with amblyopia develop after 6 to 8 years of age of life, amblyopia usually does not arise.10 Amblyopia is considered to be a developmental disorder with an early sensitive period.10, 11 This understanding has been one of the key points for the previous justification of preschool vision screening.

Treatment for amblyopia involves correcting the underlying cause of the amblyopia and reducing or eliminating the visual suppressive effect of the non-amblyopic eye. Typically this reduction or elimination is achieved by occluding the better eye with a patch. The duration of patching required depends on many factors, including the cause of the amblyopia, the density of the amblyopia, and the age of the child.

Refractive Errors Not Associated with Amblyopia. - The other common source of visual impairment is refractive error not associated with amblyopia. Examples include myopia (near-sightedness) and hyperopia (far-sightedness). These visual impairments may interfere with learning and other daily activities. Unlike amblyopia, these visual impairments remain correctable regardless of the age at which they are detected.

One challenge in evaluating refractive errors not associated with amblyopia is that refractive error often is associated with amblyopia. For example, hyperopia, the most common refractive error in children, can lead to the development of strabismus, which in turn can cause amyblopia.12

A second challenge in evaluating refractive errors in children is that the refractive state of the eye normally changes with the growth of the child.13, 14 The eye grows rapidly between birth and 3 years of age, after which growth slows. To maintain vision during the time of rapid eye growth, the lens changes geometry. Animal models suggest that this process, known as emmetropization, does not occur normally if the eye does not receive visual stimulus.13

Vision Screening Strategies. - Approaches to vision screening include assessing family history and eliciting concerns about the child's vision. Conditions associated with strabismus can be found on physical examination. For example, cataracts can be found by examining the pupillary red light reflex. Clinicians can detect strabismus using the Hirschberg test, in which the corneal light reflexes are evaluated for symmetry. Another common way to assess for strabismus is the cover test, in which the child is asked to focus on an object. Each eye is covered while the other eye is observed for movement. A strabismic eye will move to focus on an object when the non-strabismic eye is covered.

Primary care providers can employ three approaches to screen formally for visual impairment. Traditional vision screening evaluates the ability of the child to recognize letters or symbols. Examples include the HOTV chart, in which the child identifies those letters, or the Lea symbols, in which the child identifies a circle, a square, a house, or an apple.15 These figures, or optotypes, can be presented in several ways, such as on hand-held cards or on wall charts. Furthermore, they have multiple layouts, such as spacing optotypes out in a uniform fashion or crowding optotypes together.

Traditional methods for vision screening can also be used to assess stereoacuity. In these tests, the child wears polarized glasses and looks at a picture. The child with normal stereoacuity will be able to see a figure. An example of this type of test includes the Random Dot E test, in which a child with normal stereoacuity will see a floating “E.”

Binocular photoscreening is based on interpretation of a photograph of the pupils of the eyes. Patterns of reflections from the eyes can suggest refractive errors, strabismus, and cataracts. Two types of photoscreeners are presently available: those in which the screener interprets the photograph (such as MTI Photoscreener™, Medical Technology and Innovations, Inc., Lancaster, Pa.; Visiscreen 100™, Vision Research Corporation, Birmingham, Ala.) and those in which a computer interprets the photograph (such as The EyeDx System™, EyeDx, Inc., San Diego, Calif.).

The third available screening strategy involves automated devices that screen for refractive error (such as Retinomax™, Nikon Inc., Japan ; SureSight™, Welch Allyn, Inc., Skaneateles Falls, NY). These devices directly refract each eye. This strategy evaluates one eye at a time and cannot, therefore, detect a misalignment between the eyes.

Unlike photoscreening, traditional vision screening tests directly for acuity and amblyopia. The newer technologies detect refractive errors and other conditions associated with amblyopia, but they do not directly evaluate acuity. They have the advantage of requiring only minimal cooperation from the child and can, therefore, be used to screen young children.16 However, some of the current devices, such as the MTI Photoscreener™, require that the screener interpret a photograph of the eyes.


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