Methodological quality of the review: Medium confidence
Author: Smeeth L, Iliffe S.
Region: United Kingdom (UK) and Netherlands.
Sub-sector: Diagnosis, visual impairment, assessment programme.
Equity focus: Older people (aged 65 or above)
Review type: Effectiveness review
Quantitative synthesis method: Meta-analysis
Qualitative synthesis methods: Not applicable
Visual impairment seems to be common among an older population. In the UK, it is estimated that 2% of those aged 65 to 74 and 20% of those 75 and above have visual acuity of less than 6/12. This level of visual acuity is below the standard set for driving in the UK. Therefore, dating back to 1990, general practitioners have been required to offer an annual screening assessment to all patients aged 75 and over, specifically including an assessment of vision. While multiphasic screening of older people has been shown to be beneficial overall, exactly which procedures have been shown to be effective is uncertain.
To assess whether population screening for impaired vision among older people in the community leads to improvement in vision.
There were no trials that primarily assessed visual screening. Outcome data on vision were available for 3,494 people in five randomized trials of multiphasic assessment. All the trials used self-reported measures for vision impairment, both as screening tools and as outcome measures. Four studies were conducted in UK and one study was conducted in the Netherlands. The inclusion of a visual screening component in the assessments did not result in improvements in self-reported visual problems (pooled odds ratio 1.04: 95% confidence interval 0.89 to 1.22). A small reduction (11%) in the number of older people with self-reported visual problems cannot be excluded. Statistical testing showed no evidence of heterogeneity of effect in the five trials (X2=0.92, df=4, P=0.92).
All five studies adequately concealed randomization and participants were aware of whether they had received a screening treatment. Therefore, despite attempts to blind the outcome assessors, which arm of the trial subjects were in could clearly merge from face-to-face assessment of outcome.
The authors concluded that screening of asymptomatic older people in the community is not justified on present evidence. Vision impairment in this age group can usually be reduced with treatment, and authors note that it is not clear why no benefit was seen in included studies. Further work was needed to clarify what interventions were appropriate for older people with unreported impairment of vision.
The authors included randomized controlled trials of either visual or multiphasic screening of unselected subjects in a community setting that included patients aged 65 and over. Trials had to report any visual outcome data, whether formally tested or self-reported; and a follow-up of at least six months to allow intervention for detected visual problems.
The authors referred to a companion article which was used as a guide for the search strategy. In order to obtain further information this article was consulted.
The authors conducted a search on Medline for randomized controlled trials evaluating screening in older people performed for the period 1966 to 1996. The October 1997 Cochrane Library was also searched for both trials and relevant reviews. Other review articles and books were consulted and bibliographies of relevant articles were scanned. Experts in screening for older people and in ophthalmology were consulted. Reviewers also contacted named authors for correspondence for all trials identified to ask for any further unpublished data about visual screening tests used and visual outcomes. The referred article reported including studies written in languages other than English, which may indicate that the search was not restricted to English-language articles. However, the original article does not report either. Therefore, it is not clear if the search strategy of this study was restricted to articles written in English only.
Two authors independently screened articles and extracted data of included studies. Reviewers critically appraise studies in terms of allocation concealment and blinding of outcome assessors in the trials.
For data analysis the authors combined odds ratio with the fixed effects Mentel-Haenzel methods. As well as odds ratio, authors reported the relative risk. Heterogeneity between trials was tested using chi-squared test.
The authors did not discuss the generalizability of the results.
Although the authors did not restrict the search to any particular income setting, only studies from high-income countries, namely UK and Netherlands, were included in the review. Reviewers did not describe the applicability to the findings to low- and middle- income settings, but these may not be applicable due to limited resources compared to high-income settings.
There is medium confidence in the conclusions about the effects of this review. Although the search for literature covered relevant databases and contacting authors for additional studies and further information, it is not clear from the review if language bias was avoided. Therefore, we cannot be confident that relevant studies were not omitted in the review. Appropriate methods in terms of study selection and extraction were applied to minimize the risk of bias. The authors critically appraise each study in terms of allocation concealment, however, other parameters such as masking of outcome measurements, sample size planning, group comparison and confounding factors were not considered. Nevertheless, the authors do not draw strong policy conclusions and provide likely explanatory factors for the lack of improvement seen in the included trials.