Effectiveness of screening preschool children for amblyopia: a systematic review

Methodological quality of the review: High confidence

Author: Schmucker C, Grosselfinger R, Riemsma R, Antes G, Lange S,
Lagrèze W, Kleijnen.

Region: Israel, Sweden and United Kingdom (UK).

Sector: Screening

Sub-sector: Amblyopia, preschool screening, amblyogenic factors, prevalence rate.

Equity focus: Children (up to the age of six)

Review type: Effectiveness review

Quantitative synthesis method: Narrative analysis

Qualitative synthesis methods: Not applicable


In children, amblyopia and amblyogenic risk factors like strabismus and uncorrected refractive errors constitute the most common vision problems. Early treatment of such conditions is more effective than treatment later in life. Although different studies suggest that preschool vision screening is associated with a reduced prevalence rate of amblyopia, the value of these programmes is the subject of a continuing scientific and health policy discussion.

Research objectives

To determine the effectiveness of a preschool screening programme among children up to the age of six years.

Main findings

The search identified 25,944 citations after removing duplicate references. Authors included five studies (eight publications), two retrospective cohort studies, one randomized controlled clinical trial, one pseudo-randomized controlled clinical trial and one prospective study focused on unselected children from the general population up to the age of six years. Included studies covered data from Israel, Sweden and the UK. The included studies were methodologically weak: for example, no study conducted prospective sample size planning, the pseudo-randomized controlled clinical trial excluded approximately 45% of the originally recruited children in their analysis without giving any reasons for exclusion.

Three studies suggested that screening is associated with an absolute reduction in the prevalence of amblyopia between 0.9% and 1.6% (relative reduction: between 45% and 62%). On the other hand, retrospective sample size calculation indicated that the power based on the cohort size was not sufficient to detect small changes between the groups. The authors noted that outcome parameters such as quality of life or adverse effects of screening had not been adequately investigated in the literature presented.

The authors concluded that population-based preschool vision screening programmes could not be sufficiently assessed by the literature on the presented evidence. Nevertheless, they also stated that it was most likely that this systematic review contained the most detailed description of the main limitations in the current available literature evaluating these programmes. Therefore, future research work should be guided by the findings of this publication.


Inclusion criteria consisted of randomized controlled trials, non-randomized controlled trials and controlled cohort studies which compared screening methods versus no screening or compared different screening strategies; population included children from the general population up to the age of 6 years; and reported the following outcome measures: prevalence rate of amblyopia, quality of life, cognitive and educational development and adverse effects related to screening.

The authors conducted a search on different databases for published and unpublished studies including Medline, Embase, CINAHL and Cochrane Central. No date or language restrictions were applied to the search. The searches were supplemented by searching the bibliographies of included studies and reviews manually; and enquiries were sent to manufacturers of screening instruments. Authors of studies were contacted if data were unclear or appeared incomplete.

All stages of study selection, data extraction and quality assessment were done independently by two reviewers. For evaluation of the included studies a modified quality evaluation tool of the Centre for Reviews and Dissemination (CRD) was used.

The authors conducted a narrative synthesis of the findings due to the heterogeneity of included studies.

Applicability/external validity

The authors stated that based on the evidence available, vision screening could not be sufficiently assessed.

Geographic focus

Although the authors did not restrict the search to a specific income setting, only data from high-income settings were identified for inclusion. Nevertheless, it can be concluded that there is a lack of evidence in this field and that further research is needed and that this study should be used as a guide.

Quality assessment

There is high confidence in the conclusions about the effects of this review. The authors conducted a thorough search of the literature to ensure the inclusion of published and unpublished studies, avoiding language bias. Methods used in terms of study selection, data extraction and quality assessment of included studies were appropriate avoiding risk of bias. As included studies were methodologically weak, no strong policy conclusions were drawn and limitations were acknowledged.

Schmucker C, Grosselfinger R, Riemsma R, Antes G, Lange S, Lagrèze W, Kleijnen. Effectiveness of screening preschool children for amblyopia: a systematic review. BMC Ophthalmology. 2009 Source