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Chou R, Dana T, Bougatsos C. Screening for Visual Impairment in Children Ages 1-5 Years: Systematic Review to Update the 2004 U.S. Preventive Services Task Force Recommendation [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2011 Feb. (Evidence Syntheses, No. 81.)

4Discussion

Summary of Review Findings

Results of this evidence synthesis, organized by KQ, are summarized in Table 15. Vision impairment and amblyopia or amblyogenic risk factors are relatively common in preschool-aged children ages 1 to 5 years. As in the previous USPSTF review,123 direct evidence on health outcomes of preschool vision screening remains limited. On the other hand, more evidence is now available on the accuracy and comparative accuracy of common vision screening tests in preschool-aged children, and more evidence is available to understand the effectiveness and comparative effectiveness of various treatment regimens for amblyopia and unilateral refractive error (with or without amblyopia).

Table 15. Summary of Evidence.

Table 15

Summary of Evidence.

The only available randomized trial of preschool vision screening compared more intensive with less intensive screening, rather than screening versus no screening.49 Although it found that repeated preschool screening reduced the prevalence of subsequent (school-age) amblyopia by about 1 percent compared with one-time screening, the difference was only statistically significant for one of two definitions of amblyopia used in the trial. One fair-quality prospective cohort study found no significant difference between one-time screening at age 37 months compared with no screening in risk for amblyopia at age 7.5 years,50 but did find a 50 percent reduction in odds of being bullied,97 perhaps related to earlier completion of patching regimens. Retrospective cohort studies that found preschool vision screening to be more effective than no screening are of limited usefulness because of important methodological shortcomings.51–53

More evidence is now available on the accuracy of various preschool vision screening tests. There is good evidence that commonly used visual acuity tests, stereoacuity tests, cover-uncover tests, autorefractors, and photoscreeners are useful for screening, though differences among studies in the populations evaluated, screening tests evaluated, screening thresholds applied, and target conditions sought make it difficult to reach strong conclusions about how they compare with one another. In the largest study to directly compare many screening tests (the VIP study), differences in likelihood ratio estimates were generally too small to clearly distinguish superior from inferior tests.82 In addition to diagnostic accuracy, other factors that may affect the choice of screening tests include testability rates at the age being screened, convenience, costs, and how well different tests perform in combination.11, 61, 71, 80, 89 Studies11, 61, 71, 80 that evaluated combinations of clinical tests (visual acuity, stereoacuity, and ocular alignment) generally reported stronger likelihood ratios than studies that evaluated individual tests. Screening tests were generally associated with a high rate of false-positives in low-prevalence populations10–12, 60, 68, 80 which could result in unnecessary prescription of eyeglasses.98

There is good evidence that there are effective treatments for visual impairment in preschool-aged children. Although benefits of patching compared with no patching average 1 line or less of visual acuity, some trials pretreated all children with eyeglasses, and benefits appear larger (1 to 2 lines) in children with more severe baseline vision impairment.99–101 All of the trials enrolled children ages 3 years or older, so applicability to younger preschool-aged children is uncertain. Factors that may affect interpretation of the magnitude of treatment benefits are that the visual impairment associated with amblyopia can become irreversible, is not correctable with refraction, and potentially affects function over the lifespan of a child. Although patching and atropine appear to be similarly effective treatments for amblyopia,105 patching may be associated with more short-term (but usually reversible) visual acuity loss in the nonamblyopic eye compared with atropine,105 as well as more psychological distress,112 since it is a more visible treatment.

Evidence on when to initiate preschool screening remains limited. One randomized trial initiated screening at different ages, but effects of age could not be separated from effects of repeated versus one-time screening.49 Other studies indicate a lower rate of false-positive screening results in children screened at age 3.5 years compared with those screened at age 1.5 years,55 but there was no clear association between age at which treatment was started and effectiveness among preschool-aged children ages 3 years and older.99, 100, 102, 103, 109–111

Our conclusions regarding effectiveness of treatments for amblyopia are generally in accordance with Cochrane reviews on treatments for strabismic amblyopia124 and unilateral refractive amblyopia,125 even though the Cochrane reviews included studies of therapies not included in our review, as well as older (school-age) children and children with severe amblyopia, who are unlikely to be identified by screening alone.

Limitations

Our evidence review has some potential limitations. First, we excluded nonEnglish-language studies, which could introduce language bias. However, we identified no relevant nonEnglish-language studies in our literature searches. Second, there were too few studies to assess for publication bias. Third, a number of studies evaluated diagnostic accuracy of screening tests or screening programs in community-based settings and eye specialty clinics, which could limit their applicability to primary care settings. Finally, we did not attempt to construct outcomes tables, because the best evidence on screening versus no screening (a large prospective cohort study from the ALSPAC investigators49) found no benefits.

Emerging Issues

A number of trials by the PEDIG investigators on therapies for amblyopia, long-term follow-up of amblyopia treatments, and treatment of refractory amblyopia are currently under way or in the follow-up or analysis phase (for more information, go to http://pedig.jaeb.org/Studies.aspx).

Future Research

We identified several important gaps in the evidence on preschool screening for impaired visual acuity. There are no randomized trials showing that preschool vision screening is effective for improving visual or other clinical outcomes compared with no screening, and the only prospective cohort study found no clear benefit from screening.50 Well-designed studies are needed to identify optimal methods for vision screening, to understand when to begin screening (e.g., before age 3 years or after age 3 years), to define appropriate screening intervals, and to develop effective strategies for linking preschool-aged children with vision impairment to appropriate care, while avoiding unnecessary use of eyeglasses and other treatments. More studies are also needed to understand optimal amblyopia treatment regimens and to identify optimal combinations of screening tests. At this time, most evidence suggests that less intensive interventions are as effective as more intensive interventions, but minimum effective treatments are not clearly established. Finally, almost all of the trials have focused on effects of preschool vision screening and treatment on visual acuity outcomes. Trials that also address function are needed to clarify how preschool vision screening may affect school performance and other aspects of child development.

Conclusions

Direct evidence on effectiveness of preschool vision screening for improving visual acuity or other clinical outcomes remains very limited and does not adequately address the question of whether screening is more effective than no screening. However, good evidence on diagnostic accuracy and treatments suggest that preschool vision screening could lead to increased detection of visual impairment and greater improvement in visual outcomes than if children were never screened. Additional studies are needed to better understand effects of screening compared with no screening, to clarify the risk for potential unintended harms from screening (such as use of unnecessary treatments), and to define optimal time at which to initiate screening during the preschool years.

Cover of Screening for Visual Impairment in Children Ages 1-5 Years
Screening for Visual Impairment in Children Ages 1-5 Years: Systematic Review to Update the 2004 U.S. Preventive Services Task Force Recommendation [Internet].
Evidence Syntheses, No. 81.
Chou R, Dana T, Bougatsos C.

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