Screening for prevention of optic nerve damage due to chronic open angle glaucoma

Methodological quality of the review: High confidence

Author: Hatt SR, Wormald R, Burr, J

Geographical coverage: Not reported

Sector: Open angle glaucoma

Sub-sector: Screening for prevention of optic nerve damage

Equity focus: None specified

Review type: Intervention review

Quantitative synthesis method: Narrative/thematic synthesis

Qualitative synthesis method: Not applicable

Background: Open angle glaucoma (OAG) affects the central vision and its onset is asymptomatic with a slow-occurring progression. It results in irreversible blindness. Although it is a condition that fulfils the criteria for population screening, it has not been supported by other in-depth non-systematic reviews. This review examines the evidence for effectiveness of OAG screening.

Objectives: To determine the impact of screening for OAG compared with opportunistic case findings and current referral practices on the prevalence and severity of optic nerve damage due to OAG in screened and unscreened populations. This is based on the assumption that successful detection and subsequent treatment of OAG leads to a lower prevalence of advanced optic nerve damage in screened versus unscreened populations.

Main findings: There were no studies included in this review as none met the inclusion criteria. As such, authors note that screening of chronic OAG cannot be recommended. However, authors state that there is much that can be done in order to improve awareness and encourage individuals at risk to get tested.

Countries with high-quality eye care and health education should experience rare occurrences of blindness from chronic OAG compared to countries with poor and/or emerging economies. Authors recommended that high-quality randomised control trials (RCTs) can help to establish effective screening of OAG.

However, before such trials can be conducted, certain issues need to be dealt with. These include a better understanding of the testing technologies and improved quality of research in different populations in order to outline the most effective strategies with regards to individual tests and technologies, combinations of tests and test frequency. Using the most effective strategies determined, economic modelling will aid in deciding which cost (opportunity cost and cost benefit) is justifiable before committing to long-term studies. Using registers of blindness by cause for better monitoring of health outcomes in large populations can help survey the impact of prevention strategies over time.

Methodology: The types of studies that the authors considered to meet the inclusion criteria were RCTs of screening versus no screening for OAG. The eligible studies were expected to be in the form of cluster RCTs. Trials that compared different screening strategies were not included. Studies from any population were also considered. Outcome measures were also accounted for in terms of primary and secondary outcomes.

The authors searched the Cochrane Central Register for Controlled Trials, MEDLINE, EMBASE, the UK Clinical Trials Gateway and ZETOC. There were no restrictions on language or dates in the searches carried out. There were no manual searches of journals or conferences carried out for this review. All the titles and abstracts searched were independently reviewed by two reviewers. No trials were identified that met the inclusion criteria. However, the authors mention updating the review should any reports become available in the future using the methods described below.

Future eligible studies will be assessed independently for their methodological quality by two reviewers. The parameters will be graded as low, high or unclear risk of bias based on the Cochrane Handbook for Systematic Reviews of Intervention. A Drummond checklist for the critical appraisal of economic evaluations will be carried out for the economic assessment of the study.  Data extraction will then be carried out by two independent authors for the relevant studies using Cochrane Eyes and Vision Groups developed forms. These two authors will then independently enter the data extracted into the RevMan software to check for errors. In case of identified errors or unclear information, the corresponding authors of the studies will be contacted.

Screened and unscreened populations will be compared and the results from included trials will be combined in a meta-analysis using a random-effects model unless only a few trials are included, which will require a fixed-effects model. Using sub-group analysis where possible, the effectiveness of different screening strategies to no screening strategies or current practices will be compared.

Heterogeneity will be assessed by investigating the characteristics of the studies included and observing the confidence interval overlaps in the forest plots. Statistical heterogeneity will be tested using the chi-squared test in RevMan. To quantify possible inconsistencies between studies, the I2 test will be carried out.

A sensitivity analysis will also be carried out by repeating the analysis and excluding studies that have a low methodological quality (on any parameter) or if the assessor masking was lacking.

Applicability/external validity: Since there are no studies included in this review that met the inclusion criteria, the authors suggest that high quality RCTs are necessary in order to establish effective screening for OAG.

Geographic focus: Since no trials were included there is no mention of the geographic focus.


Summary of quality assessment: Overall, there is high confidence in the conclusions about the effects of this study. Although identified studies did not meet the inclusion criteria, authors used appropriate methods to identify studies for inclusion.

Publication source: Hatt SR, Wormald, R, Burr, J. (2009) Screening for prevention of optic nerve damage due to chronic open angle glaucoma (review). Cochrane Database Syst Rev. 2006 Source