Vision Screening for Children 36 to <72 Months: Recommended Practices

Purpose. This article provides recommendations for screening children aged 36 to younger than 72 months for eye and visual system disorders. The recommendations were developed by the National Expert Panel to the National Center for Children's Vision and Eye Health, sponsored by Prevent Blindness, and funded by the Maternal and Child Health Bureau of the Health Resources and Services Administration, United States Department of Health and Human Services. The recommendations describe both best and acceptable practice standards. Targeted vision disorders for screening are primarily amblyopia, strabismus, significant refractive error, and associated risk factors. The recommended screening tests are intended for use by lay screeners, nurses, and other personnel who screen children in educational, community, public health, or primary health care settings. Characteristics of children who should be examined by an optometrist or ophthalmologist rather than undergo vision screening are also described.Results. There are two current best practice vision screening methods for children aged 36 to younger than 72 months: (1) monocular visual acuity testing using single HOTV letters or LEA Symbols surrounded by crowding bars at a 5-ft (1.5 m) test distance, with the child responding by either matching or naming, or (2) instrument-based testing using the Retinomax autorefractor or the SureSight Vision Screener with the Vision in Preschoolers Study data software installed (version 2.24 or 2.25 set to minus cylinder form). Using the Plusoptix Photoscreener is acceptable practice, as is adding stereoacuity testing using the PASS (Preschool Assessment of Stereopsis with a Smile) stereotest as a supplemental procedure to visual acuity testing or autorefraction. Conclusions. The National Expert Panel recommends that children aged 36 to younger than 72 months be screened annually (best practice) or at least once (accepted minimum standard) using one of the best practice approaches. Technological updates will be maintained at http://nationalcenter.preventblindness.org. (Optom Vis Sci 2015;92:6Y16)
T he purpose of this article is to provide recommendations for screening children aged 36 to younger than 72 months for disorders of the eyes and visual system, primarily amblyopia, strabismus, significant refractive error, and risk factors associated with these disorders. The screening may be performed in educational-, community-, or public healthYbased settings or in the medical home using recommended methods that are appropriate for the screening venue. The tests recommended herein are intended for vision screenings conducted by lay screeners, school nurses, and other screening personnel in public health settings, primary health care practices, or the child's medical home to identify children in need of further evaluation by an eye care professional.
This article describes best practices supported by available research evidence, as well as acceptable standards for the conduct of vision screening in children aged 36 to younger than 72 months. Using best practice standards should be the goal for all vision screening programs.

## Rationale for vision screening
Amblyopia and its primary risk factors, strabismus and significant refractive error, 1,2 are the most common visual disorders in preschool children.The prevalence of amblyopia among children aged 36 to younger than 72 months in the United States is about 2%. 4Y6 Strabismus, a contributor to amblyopia and a disorder with significant psychosocial consequences, [bib_ref] Psychosocial aspects of strabismus study, Satterfield [/bib_ref] [bib_ref] Strabismus and discrimination in children: are children with strabismus invited to fewer..., Mojon-Azzi [/bib_ref] has an estimated prevalence of 2.1 to 3.6% in preschool children. The prevalence of significant refractive error, a condition more widespread than amblyopia and strabismus combined, is dependent on race/ethnicity, age, and the type of refractive error and criterion used to define the magnitude considered significant. 9Y13 For example, recent populationbased estimates in a multiethnic cohort of children aged 6 to younger than 72 months found the prevalence of hyperopia greater than or equal to 2.00 diopters (D) and astigmatism greater than or equal to 1.50 D in Hispanic children to be 26.9 and 16.8%, respectively, whereas the prevalence in African American children was 20.8% for hyperopia and 12.7% for astigmatism. [bib_ref] Prevalence of myopia, hyperopia, and astigmatism in non-Hispanic white and Asian children:..., Wen [/bib_ref] [bib_ref] Prevalence of astigmatism in 6-to 72-month-old African American and Hispanic children: The..., Fozailoff [/bib_ref] Not all of these children, however, have amblyogenic refractive error or refractive error significant enough to warrant an optical correction. The US Preventive Services Task Force (USPSTF) recommends that children between the ages of 3 and 5 years be screened at least once to detect the presence of amblyopia and amblyogenic risk factors such as strabismus and significant refractive error.Whereas vision screening is typically easier in school-aged children 6 years and older, evidence suggests that the success of amblyopia treatment is influenced by a child's age, with children younger than 7 years old being more responsive to amblyopia treatment. [bib_ref] Effect of age on response to amblyopia treatment in children, Holmes [/bib_ref] The recent USPSTF report concluded that there is adequate evidence that early treatment of amblyopia results in improved visual outcomes.In addition, optical correction of significant refractive error may be related to child development [bib_ref] Child development and refractive errors in preschool children, Ibironke [/bib_ref] and may improve school readiness. [bib_ref] Ametropia, preschoolers' cognitive abilities, and effects of spectacle correction, Roch-Levecq [/bib_ref] [bib_ref] Infant vision screening predicts failures on motor and cognitive tests up to..., Atkinson [/bib_ref] The USPSTF recommends that children undergo vision screening at least once between the ages of 36 and 72 months instead of waiting until children are schoolaged. Ongoing and periodic vision screening during the school years, however, is also important for school-aged children not receiving comprehensive eye examinations because refractive errors and other visual disorders may develop during this time.

## Recommendation development
In 2009, the Maternal and Child Health Bureau, recognizing the importance of early vision and eye health, funded the establishment of the National Center for Children's Vision and Eye Health at Prevent Blindness. A National Expert Panel (NEP) composed of leading professionals in ophthalmology, optometry, pediatrics, public health, and related fields was formed to advise the Center on how best to improve the public health infrastructure supporting the early detection of children's vision problems. The NEP specifically addressed vision screening methodology and the system of care needed to ensure appropriate, subsequent referral for professional eye evaluation and management. The NEP undertook a literature review (through February 2014) of the evidence base underlying vision screening of children aged 36 to younger than 72 months, supplementing their evaluation of the literature with the group's clinical experience where necessary. The rationale and process used to develop the recommendations are fully described in the Appendix, available at http://links.lww.com/OPX/A187. Screening methods designated herein as ''best practice'' are considered to have a sufficient evidence base from well-designed and well-conducted vision screening studies of children aged 36 to younger than 72 months to support their use in the educational, community, public health, or primary health care environments. Methods considered to be ''acceptable practice'' have some peer-reviewed published literature, but an insufficient level of evidence for the best practice categorization, generally because of small sample size, flaws in study design, or limited generalizability to the targeted age group or mass vision screening environment.
The NEP has written three reports targeting children aged 36 to younger than 72 months with recommendations for (1) conducting quantitative vision screening, [bib_ref] Risk factors for decreased visual acuity in preschool children: the multi-ethnic pediatric..., Tarczy-Hornoch [/bib_ref] building an integrated data system to track vision screening and subsequent eye care, [bib_ref] for the National Expert Panel to the National Center for Children's Vision..., Hartmann [/bib_ref] and (3) specifying recommendations for developing state-level performance measures to track progress toward the goal of providing high-quality vision screening and follow-up to all preschool-aged children. [bib_ref] Repka MX; for the National Expert Panel to the National Center for..., Marsh-Tootle [/bib_ref] This document is the first of the three reports and provides vision screening recommendations for children aged 36 to younger than 72 months that incorporate best practices based on currently available evidence. These practices should be reviewed periodically, at least every 5 years, with revised information available on the Web site for the National Center for Children's Vision and Eye Health (http://nationalcenter.preventblindness.org).

## Children requiring automatic referral for examination
Children at high risk for vision disorders and those with readily recognized eye abnormalities such as strabismus or ptosis should be referred directly, and in a timely manner, to an appropriate eye care professional. Because children with known neurodevelopmental disorders (e.g., hearing impairment, motor abnormalities such as cerebral palsy, Down syndrome, cognitive impairment, autism spectrum disorders, or speech delay) have a higher rate of vision problems than those without neurodevelopmental abnormalities, 20Y24 they should be referred directly to an optometrist or ophthalmologist for a comprehensive eye examination. Children with systemic diseases or using medications known to cause eye disorders, those with a family history of a first-degree relative with strabismus or amblyopia, and children born prematurely at less than 32 completed weeks of gestation also should receive a comprehensive eye examination rather than be screened. 2,25Y27 Additionally, when a parent or guardian believes his or her child may have a vision-related problem, an eye care professional should examine that child. Because the purpose of vision screening is to identify children in need of further care, those who have received a comprehensive eye examination from an eye doctor within the previous 12 months do not need to be screened but should be referred back to their eye doctor for follow-up.

## Vision screening process
In general, there are two vision screening approaches [fig_ref] TABLE 1: Best practices for vision screening children aged 36 to younger than 72... [/fig_ref] for children aged 36 to younger than 72 months, each with advantages and disadvantages. The first method is a monocular measure of recognition visual acuity using an age-appropriate technique. The alternative approach is to use instrumentbased screening methods (autorefraction or photoscreening) to identify amblyogenic risk factors, particularly significant refractive error.All screening personnel should undergo a comprehensive training program, preferably with standardized training and certification in the screening methods to be used, with subsequent continuing education and formal recertification every 3 to 5 years. Tests such as red reflex testing for media opacity detection or cover testing for eye misalignment should only be used as part of the vision screening process if administered by health care personnel professionally trained to perform and interpret the tests. When performed alone, neither test provides sufficient information for a full vision screening, [bib_ref] Comparison of preschool vision screening tests as administered by licensed eye care..., Schmidt [/bib_ref] [bib_ref] The Bruckner test: detection of strabismus & amblyopia in infants & young..., Huang [/bib_ref] although detection of an abnormality should trigger referral for a comprehensive eye examination.
Selecting the vision screening method to be used depends on the screening venue, availability of screening personnel, time allotted for the screening, and funding resources. Ideally, a vision screening program should consist of a single cost-effective test that can be quickly and easily administered by nonmedical personnel to the target population in any environment. Significant training should not be required; the child's cooperation should not be essential; missed referrals and unnecessary referrals should be nonexistent; and the screening results should automatically be integrated into an electronic health record. Any real-world screening method represents a trade-off among all of these factors. Screening programs can be designed to use a single screening test or a combination of more than one test. However, combining two screening tests does not necessarily result in the highest sensitivity and specificity from each component test. [bib_ref] Assessing the gain in diagnostic performance when combining two diagnostic tests, Macaskill [/bib_ref] The strengths and weaknesses of currently available vision screening methods are described below.

## Recognition visual acuity screening
Visual acuity is the quantifiable measure of the ability to identify black symbols on a white background at a standardized test distance. The most commonly measured type, recognition visual acuity, is defined as the ability to discern certain optotypes (letters, numbers, or figures) at a specified distance. Ideally, tests of visual acuity should have the same number of optotypes for each acuity level and the same proportional decrease in size from one acuity level to the next smaller level in logMAR (logarithm of the minimum angle of resolution) progression. [bib_ref] New design principles for visual acuity letter charts, Bailey [/bib_ref] Visual acuity methods for vision screening are widely used for adults and school-aged children. To be performed reliably in children aged 36 to younger than 72 months, however, a number of testing modifications are required [fig_ref] TABLE 2: Distance visual acuity testing for vision screening of children aged 36 to... [/fig_ref]. [bib_ref] Visual acuity of the preschool child: a review, Fern [/bib_ref] [bib_ref] The measurement of visual acuity in children: an evidence-based update, Anstice [/bib_ref] These include using age-appropriate and adequately illuminated test symbols that can be presented in random order and using a lap card (i.e., card with the test optotypes that the child places on his or her lap) for matching, administering a pretraining or demonstration session before the start of testing to confirm that the child understands and can perform the test, and using a closer test distance. Ideally, the test environment should be quiet and free of distraction, the wait time short, and the child approached in a manner that maximizes his or her cooperation (such as presenting the screening task as a game rather than as a test). The parents and/or teachers of the child to be screened should be fully informed about the importance of vision screening and ideally be provided with practice cards to be used before screening.

## Testing symbols
The HOTV [bib_ref] Vision of young children, Lippmann [/bib_ref] [bib_ref] Preschool visual acuity screening tests, Friendly [/bib_ref] and LEA Symbols, [bib_ref] New visual acuity test for preschool children, Hyvarinen [/bib_ref] two tests that were developed for use in preschool children, [bib_ref] The measurement of visual acuity in children: an evidence-based update, Anstice [/bib_ref] [bib_ref] Threshold visual acuity testing of preschool children using the crowded HOTV and..., Cyert [/bib_ref] [bib_ref] Comparison of the HOTV and Lea Symbols charts for preschool vision screening, Hered [/bib_ref] are presently considered best practice for visual acuity testing of children aged 36 to younger than 72 months. The letters H, O, T, and V have vertical symmetry, and the LEA Symbols consist of four picture optotypes (house, heart/apple, circle, and square) that blur equally. [bib_ref] New visual acuity test for preschool children, Hyvarinen [/bib_ref] Although 3-year-old Head Start children have been reported to achieve better visual acuity scores with the LEA Symbols, no statistically significant differences in sensitivity between the tests were found for 3-, 4-, or 5-year-old children.While HOTV optotypes are used more commonly in preschool-aged epidemiological studies 4,42Y44 and randomized clinical trials for amblyopia, 45Y47 most children 3 years and older can successfully complete visual acuity testing using either set of optotypes.Snellen optotypes are not recommended for the measurement of visual acuity in preschool-aged children. Children this age do not know their letters sufficiently well and the letters are not equally detectable. Because Landolt C and Tumbling E tests require discrimination of left-right directionality (rightward vs. leftward pointing), a skill that is not sufficiently developed in preschool children, [bib_ref] Learning to perceive and perceiving to learn, Pick [/bib_ref] these tests should also not be used. Picture charts, such as the Allen Preschool Vision Test and the Kindergarten Eye Chart, are also problematic because they are not standardized. Both have variable interline gap widths and shape cues resulting in some of the pictures being more readily identified than others. [bib_ref] The measurement of visual acuity in children: an evidence-based update, Anstice [/bib_ref] When pictures are too easily recognized, visual acuity is overestimated in children with amblyopia. [bib_ref] Visual acuity of the preschool child: a review, Fern [/bib_ref] [bib_ref] Comparison of visual acuity levels in pediatric patients with amblyopia using Wright..., Mocan [/bib_ref] [bib_ref] Modified Allen pictures to assess amblyopia in young children, Mayer [/bib_ref] Furthermore, some of the pictures have a cultural bias and others are outdated, making the pictures not readily recognizable by all children.

## Symbol presentation and crowding bars
When a small number of optotypes such as the HOTV or LEA Symbols are used in testing, the possible responses are limited. On any presentation of four letters, the probability of guessing three of four optotypes correctly is about 5%. [bib_ref] The amblyopia treatment study visual acuity testing protocol, Holmes [/bib_ref] Thus, any given visual acuity level is considered to be passed if three of three or three of four optotypes are correctly identified at that particular level. Although the presentation of single optotypes generally improves testability, the use of single isolated optotypes substantially reduces the sensitivity for the detection of amblyopia. [bib_ref] Visual acuity norms in young children, Simons [/bib_ref] Surrounding single optotypes with four flanking bars that create a ''crowding effect'' improves amblyopia detection. [bib_ref] Visual resolution and contour interaction, Flom [/bib_ref] [bib_ref] Contour interaction and visual resolution: contralateral effects, Flom [/bib_ref] Isolated HOTV or LEA optotypes with crowding bars presented in printed format or by computer have been used successfully in large-scale studies of preschool children and are considered best practice for measuring visual acuity in children aged 36 to younger than 72 months. A single line of optotypes with crowding bars on all four sides extended to form a crowding rectangle surrounding the line of optotypesis also preferable to isolated optotypes without crowding bars; this type of presentation is considered acceptable practice.

## Occlusion for visual acuity testing
Visual acuity testing should be conducted separately for each eye because unilateral amblyopia is masked by the better-seeing eye when amblyopic children are tested binocularly. Screening personnel need to monitor occlusion carefully because children with reduced vision in one eye often attempt to use their better eye by peeking. Preferred methods of occlusion are to use adhesive eye patches or 2-in wide hypoallergenic surgical tape (e.g., Micropore or Blenderm). An acceptable method is the use of specially constructed occluder glasses (e.g., Good-Lite opaque occluder glasses). Holding a tissue, hand, paper cup, or an occluder paddle over a child's eye is not acceptable because children can easily circumvent these types of occlusion.

## Testing distance
The optimum test distance for measuring visual acuity in children aged 36 to younger than 72 months is shorter than that used for adults and school-aged children. The advantages of a shortened test distance include improved ability to maintain the child's attention and the ability to test the child in a smaller space, thereby avoiding the distractions of a crowded hallway or large testing room. The best practice for children this age is to use single surrounded optotypes at a 5-ft (1.5-m) test distance.Significantly increased sensitivity for a given level of specificity, equal to that obtained by eye doctors, has been found when lay screeners use single surrounded LEA Symbols at the 5-ft (1.5-m) test distance

## Illumination of test materials
Visual acuity testing is best performed with good illumination and maximum contrast (at least 85%) between the black symbol and the white background.Best practices for illumination are using a lightbox with a translucent visual acuity chart, a lighted stand designed to hold and evenly illuminate the acuity test, or a computer screen display. Insufficient illumination of the test material (G80 cd/m 2 )and competing light sources that create glare or uneven illumination (e.g., testing performed beside a window) should be avoided because they can negatively affect visual acuity measurements.

## Pass/fail criteria for visual acuity testing
The passing criterion for HOTV or LEA Symbols is age specific and must be met by both the right and left eyes separately. Children aged 36 through 47 months must identify correctly three of three or three of four of the 20/50 (5/12.5) optotypes to pass; children aged 48 to younger than 72 months must correctly identify the same number of optotypes at the 20/40 (5/10) level. [bib_ref] Prevalence of amblyopia and strabismus in white and African American children aged..., Friedman [/bib_ref] [bib_ref] Comparison of preschool vision screening tests as administered by licensed eye care..., Schmidt [/bib_ref] Children who do not meet these age-specific criteria for each eye should be referred for a comprehensive eye examination.

## Instrument-based vision screening
Instrument-based screening refers to vision screening using automated technology. Generally, instrument-based screening is quick to administer and requires minimal cooperation from the child, thereby making it especially useful for shy, noncommunicative, or preverbal children. Using an automated instrument also offers the advantage of having the potential for the screening results to be integrated directly into a data management system without requiring manual data entry. A recent policy statement published by the American Academy of Pediatrics noted that an instrument-based approach can be used in the medical home as an alternative to visual acuity screening for children aged 3 through 5 years. 29

## Refractive instrument-based methods of vision screening
Instrument-based screening using autorefraction or photorefraction/ photoscreening identifies the presence and magnitude of refractive error rather than providing a measurement of visual acuity. Each of these screening devices requires instrument-and age-specific pass/ fail refractive error criteria. Abnormal refractive error is a significant risk factor for amblyopia. [bib_ref] Risk factors for decreased visual acuity in preschool children: the multi-ethnic pediatric..., Tarczy-Hornoch [/bib_ref] Hyperopic refractive error greater than or equal to 2.00 D spherical equivalent, in particular, is associated with a significantly higher risk of esotropia, [bib_ref] Risk factors associated with childhood strabismus: The Multi-ethnic Pediatric Eye Disease and..., Cotter [/bib_ref] which by itself is an additional risk factor for amblyopia. Because of the association among amblyopia, strabismus, and uncorrected significant refractive error, screening for refractive error alone is often successful in identifying children with constant strabismus and moderate to severe levels of amblyopia. [bib_ref] Comparison of preschool vision screening tests as administered by licensed eye care..., Schmidt [/bib_ref] Autorefraction Autorefractors are computerized instruments that use optically automated skiascopy methods or wave-front technology to provide a numeric estimate of refractive error. When used for vision screening purposes, the operator or the instrument must interpret the refractive error measurement as a pass or fail. Although accurate determination of refractive error (hyperopia in particular) requires the instillation of eye drops to provide cycloplegia, eye drops are not used in the screening environment. Accordingly, vision screening by autorefraction only provides an estimate of refractive error; it is not a substitute for an eye examination and refraction by an ophthalmologist or optometrist.
Unlike tabletop models that are often difficult to use with young children, handheld autorefractors are suitable for vision screening because they are portable and only require a few seconds of a child's attention. At the time of this publication, two handheld autorefractors, the Retinomax (Right Mfg Co Ltd, Tokyo, Japan) and the SureSight Vision Screener (SureSight) (Welch-Allyn, Inc, Skaneateles Falls, NY), have high-quality published performance data in the targeted age range and are commercially available with the appropriate Food and Drug Administration designation; thus, they meet the criteria for best practice for preschool vision screening. [bib_ref] Comparison of preschool vision screening tests as administered by licensed eye care..., Schmidt [/bib_ref] The Vision in Preschoolers (VIP) Study has shown that these two autorefractors meet or exceed the screening performance achieved using recognition visual acuity testing in preschool children. [bib_ref] Comparison of preschool vision screening tests as administered by licensed eye care..., Schmidt [/bib_ref] The Retinomax has a high testability rate [bib_ref] Testability of the Retinomax autorefractor and IOLMaster in preschool children: the Multi-ethnic..., Borchert [/bib_ref] [bib_ref] Testability of refraction, stereopsis, and other ocular measures in preschool children: the..., Pai [/bib_ref] and good sensitivity at both 0.90 and 0.94 specificity in children aged 36 to younger than 72 months [bib_ref] Comparison of preschool vision screening tests as administered by licensed eye care..., Schmidt [/bib_ref] ; however, the results are reported in ophthalmic prescription format, which is not readily interpretable by most lay screeners. The SureSight, when used in the ''child mode,'' provides the operator with a pass or fail determination. Although the manufacturer's preprogrammed pass/fail criteria do not perform well in identifying amblyopia and amblyogenic conditions in preschool children, [bib_ref] Comparison of preschool vision screening tests as administered by licensed eye care..., Schmidt [/bib_ref] software is available (version 2.24 or 2.25, School Health Corp, Hanover Park, IL) for the SureSight (when used in minus cylinder format) that incorporates the betterperforming VIP Study pass/fail criteria for 90% specificity. [bib_ref] Comparison of preschool vision screening tests as administered by licensed eye care..., Schmidt [/bib_ref] In addition to refractive error data, an asterisk is displayed on the printout when a child fails according to the VIP referral criteria, thus facilitating interpretation of the results for screeners who are not eye professionals. Although there are a number of prior software versions that have been distributed, the NEP recommends that software version 2.24 or 2.25 be used for preschool vision screenings when the SureSight is used.

## Photorefraction/photoscreening
Photorefraction or photoscreening devices use optical images of the eyes' red reflexes to provide a simultaneous, binocular estimate of refractive error. In addition, some instruments have the capability to evaluate ocular alignment and identify media opacities. Depending on the instrument, the output is interpreted by the operator, a central reading center, or a computer. Some instruments allow the implementation of user-defined refractive error criteria to determine the pass/fail cutoffs.
In a large multicenter study that compared various preschool vision screening tests, the three photoscreening instruments evaluated (MTI Photoscreener, Power Refractor II, and iScreen Photoscreener) were found to have unsatisfactory sensitivity in detecting amblyopia, strabismus, and significant refractive error compared with the Retinomax and SureSight autorefractors. [bib_ref] Comparison of preschool vision screening tests as administered by licensed eye care..., Schmidt [/bib_ref] Since that time, a number of new or updated photoscreening devices have been introduced to the market, although none has yet undergone the same type of rigorous evaluation.
One of these newer instruments, the Plusoptix Photoscreener (Plusoptix, Nuremberg, Germany), is a binocular device based on the aforementioned Power Refractor II. Considered by some investigators to hold promise for preschool vision screenings, [bib_ref] Performance of the plusoptiX S04 photoscreener for the detection of amblyopia risk..., Matta [/bib_ref] the Plusoptix provides a simultaneous measure of autorefraction and eye alignment and allows the user to specify the desired pass/fail criteria. The device also provides a report containing the child's name, results, and pass/fail status that can be integrated into an electronic medical record.
Comparisons of the Plusoptix and clinical examination results in nonscreening settings have been mixed, 59Y63 and there are limited results available that apply to a vision screening environment for children aged 36 to younger than 72 months. [bib_ref] Field testing of the plusoptiX S04 photoscreener, Arthur [/bib_ref] Investigators have cautioned that the specificity of the Plusoptix is unacceptably low (37%) for field use when the manufacturer's pass/fail criteria are used, [bib_ref] Modification of Plusoptix referral criteria to enhance sensitivity and specificity during pediatric..., Nathan [/bib_ref] and while modifications of these criteria can result in improved specificity without loss of sensitivity, the ideal refractive error criteria have yet to be determined. [bib_ref] Modification of Plusoptix referral criteria to enhance sensitivity and specificity during pediatric..., Nathan [/bib_ref] Of note, consensus-based refractive error criteria that are thought to place young children at risk for the development of amblyopia and thereby warrant detection by vision screening 66 are based on cycloplegic refractions; these are not intended to be used as cutoff values for vision screening instruments that measure noncycloplegic refractive error. [bib_ref] A comparison of referral criteria used by the PlusoptiX photoscreener, Singman [/bib_ref] Despite these limitations and lack of robust evidence, the NEP's opinion is that the Plusoptix instrument appears sufficiently promising to be classed as an acceptable practice at this time, with the caveat that the optimum refractive error referral criteria have yet to be determined. [bib_ref] Modification of Plusoptix referral criteria to enhance sensitivity and specificity during pediatric..., Nathan [/bib_ref] Thus, when the Plusoptix is used outside of an eye care setting, consultation with a pediatric eye care professional regarding the best cutoffs to use for the particular patient population to be screened is advised until evidence-based refractive error criteria are determined.
There are a number of other commercially available screening instruments that also lack high-quality published data supporting their use for vision screening children aged 36 to younger than 72 months. The recommendation of best practice for the Plusoptix and other screening devices will require validation studies. An ideal validation study consists of a prospective large-scale vision screening performed by lay screeners in the field, in which all children who pass and fail the screening also receive a comprehensive eye examination (including a cycloplegic refraction) from an optometrist or ophthalmologist masked to the results of the screening. The children screened should be within the targeted age range and also have a wide variety of vision disorders, particularly strabismus, amblyopia, and high refractive error. This type of rigorous assessment is necessary to determine the optimum refractive error referral criteria for a particular instrument. [bib_ref] Modification of Plusoptix referral criteria to enhance sensitivity and specificity during pediatric..., Nathan [/bib_ref] Because autorefractor and photoscreening technologies are evolving rapidly, recommendations for best practice will likely change with the availability of additional quality peer-reviewed data and as the natural history of refractive error and the role of risk factors for the development of amblyopia and strabismus become more clear. [bib_ref] Guidelines for automated preschool vision screening: a 10-year, evidence-based update, Donahue [/bib_ref] Updated information will be found on the Web site for the National Center for Children's Vision and Eye Health (http://nationalcenter. preventblindness.org).

## Nonrefractive instrument-based methods of vision screening
Analogous to auditory evoked brain response methods of newborn hearing screening, there are computerized systems that assess the integrity and maturation of the visual system through measurement of the electroencephalographic visual evoked response, [bib_ref] A new visual evoked potential system for vision screening in infants and..., Simon [/bib_ref] thereby providing information regarding the functional integrity of the visual system. Another approach for vision screening that is currently under investigation is retinal birefringence scanning, [bib_ref] Pediatric Vision Screener 1: instrument design and operation, Hunter [/bib_ref] [bib_ref] Rapid, high-accuracy detection of strabismus and amblyopia using the pediatric vision scanner, Loudon [/bib_ref] which simultaneously detects both the child's ability to accurately align the fovea of each eye to a common point in space and focus each fovea on that point. At present, there is insufficient evidence to recommend either of these methods for screening children aged 36 to younger than 72 months over either visual acuity testing or acceptable instrument-based methods of vision screening.

## Stereoacuity testing for vision screening
Stereoacuity (depth perception) testing performed in isolation has not been a fruitful preschool vision screening method. [bib_ref] Comparison of preschool vision screening tests as administered by licensed eye care..., Schmidt [/bib_ref] However, when combined with the SureSight Vision Screener, the Stereo Smile II test has been shown to increase the detection rate of strabismus (an amblyogenic condition).Because two screening tests do not necessarily result in a higher detection rate as compared with each test alone, 32 whether to add stereoacuity testing is dependent on the goals of the screening program and resources available. In instances when stereoacuity testing is required or desired for screening preschool children, the Stereo Smile II test, which is commercially available as the PASS (Preschool Assessment of Stereopsis with a Smile) test (Vision Assessment Corporation, Elk Grove Village, IL), should be used because it performs better than the Random Dot E test of stereoacuity. [bib_ref] Comparison of preschool vision screening tests as administered by licensed eye care..., Schmidt [/bib_ref] As new research emerges, the role of stereoacuity testing in combination with other vision screening tests will be reviewed.

## Untestable children and rescreening guidelines
Children who are inattentive, are uncooperative, will not allow one eye to be covered for monocular visual acuity testing, or do not appear to understand the screening task are not considered to have failed, but instead are deemed ''untestable'' [fig_ref] FIGURE 1: FIGURE 1. [/fig_ref]. Untestable preschool children are about twice as likely to have a vision problem than those who successfully pass a screening.If practical, untestable children should be rescreened the same day. When a same-day rescreening is not feasible, rescreening should be scheduled as soon as possible, but in no case later than 6 months. Because children unable to be screened with visual acuity testing can often complete autorefraction testing and vice versa,one should consider using the alternate method for rescreening if both are available. Untestable children with cognitive, physical, or behavioral issues that are likely to preclude successful rescreening, children who are unable to be rescreened within 6 months, and those who fail rescreening should be referred directly for a comprehensive eye examination by an optometrist or ophthalmologist [fig_ref] FIGURE 1: FIGURE 1. [/fig_ref].

## Components of a comprehensive vision screening program
Vision screening of children aged 36 to younger than 72 months, which is recommended by the USPSTF,can be performed either by measuring recognition visual acuity directly or by using instrumentbased methods of autorefraction or photoscreening to identify amblyogenic refractive error. Sufficient evidence showing that either method is effective when the aforementioned best practice testing methods are used has accumulated. [bib_ref] Comparison of preschool vision screening tests as administered by licensed eye care..., Schmidt [/bib_ref] The number of children to be screened, time allotted for screening, available budget for implementing the screening program, and reporting requirements will be factors in determining whether a recognition visual acuityYbased screening program, an instrument-based program, or a hybrid of the two is used.
Regardless of the screening method(s) selected and whether the child passes or fails the vision screening, the screening system is only successful when the results are used in a meaningful way. Screening results must be recorded and communicated to the child's parents, and as appropriate to the medical home/primary care provider, the school, and necessary state agency, with subsequent referral to an ophthalmologist or optometrist for examination and care when indicated. Specific data systems must be established to facilitate this process [bib_ref] for the National Expert Panel to the National Center for Children's Vision..., Hartmann [/bib_ref] and programs should monitor overall system performance at the population level to ensure that screening goals are being met. [bib_ref] Repka MX; for the National Expert Panel to the National Center for..., Marsh-Tootle [/bib_ref] SUMMARY OF RECOMMENDATIONS 1. All children aged 36 to younger than 72 months should be screened annually (best practice) or at least once (acceptable minimum standard) during the interval between their third and sixth birthdays. Exceptions to this include children with the following: readily observable ocular abnormalities, neurodevelopmental disorders, systemic conditions that have associated ocular abnormalities, first-degree relatives with strabismus or amblyopia, a history of prematurity (G32 completed weeks), and parents who believe their child has a vision problem. These children should be referred directly to an ophthalmologist or optometrist for a comprehensive eye examination. Children who have received an eye examination from an eye care professional within the prior 12 months do not need to be screened. A vision screening program based on best practice standards should be the goal. 2. Children who are unable or refuse to complete testing are considered untestable. These children are more likely to have vision problems than testable children,and thus should be rescreened either the same day or soon afterward, but in no case later than 6 months. Children with cognitive, physical, or behavioral issues likely to preclude rescreening and those unable to be rescreened in a timely manner because of administrative or other issues should be referred directly for a comprehensive eye examination. 3. Currently, there are two best practice vision screening methods for children aged 36 to younger than 72 months: (1) monocular vision acuity testing and (2) instrument-based testing using autorefraction. For visual acuity testing, appropriately scaled (logMAR) single crowded HOTV letters or LEA Symbols surrounded by crowding bars at a 5-ft (1.5-m) test distance with the child matching or reading the optotypes aloud should be used. A passing score is the correct identification of three of three or three of four optotypes with each eye at the 20/50 level for children aged 36 through 47 months and at the 20/40 level for children aged 48 to younger than 72 months. Acceptable practices are to use the HOTV or LEA Symbols calibrated for a 10-ft (3-m) test distance or to use a single line of these optotypes surrounded by a rectangular crowding bar on all four sides. Other optotypes like Allen pictures and the Tumbling E should not be used. The other best practice vision screening method is instrument-based screening using either the Retinomax autorefractor or the SureSight Vision Screener set in child mode and programmed with the VIP Study pass/fail criteria software for 90% specificity (version 2.24 or 2.25) in minus cylinder form. Using the Plusoptix photoscreener is considered acceptable practice, as is adding the PASS stereoacuity test as a supplement to one of the best practice screening methods. 4. Vision screening requires training and certification of screening personnel, acquiring sufficient and appropriate space, obtaining and maintaining equipment and supplies, as well as recording and reporting the screening results to the family, primary care provider/medical home, and when indicated the school or appropriate state agency. 5. A best practice for children who fail vision screening includes documentation of the referral to and subsequent comprehensive eye examination by an optometrist or ophthalmologist. 6. A range of resources to support implementation of these recommendations, including demonstrations of the vision screening process, can be found at http://nationalcenter. preventblindness.org.

# Conclusions
It is the NEP's intent that this summary will prove useful for eye care professionals playing a leadership role in ensuring that children aged 36 to younger than 72 months in their communities receive high-quality vision screening and appropriate follow-up.

# Acknowledgments
Members of the NEP to the National Center for Children's Vision and Eye Health
[fig] FIGURE 1: FIGURE 1. [/fig]
[table] TABLE 1: Best practices for vision screening children aged 36 to younger than 72 months Increased cost if computer-based system m, meters; cd, candelas.8 Vision Screening Children 3-to 6-Year Olds: Proposed Data DefinitionsVCotter et al. [/table]
[table] TABLE 2: Distance visual acuity testing for vision screening of children aged 36 to younger than 72 months [/table]