Authors: Kárason KT, Vo D, Grauslund J, Rasmussen ML.

Geographical coverage: The USA, the UK, Denmark, Germany, France and Italy

Sector: Service delivery

Sub-sector: Screening, imaging

Equity focus: Not reported

Study population: Patients with diabetic retinopathy

Review type: Other review

Quantitative synthesis method: Not applicable

Qualitative synthesis method: Narrative synthesis

Background: Diabetic retinopathy (DR) is a leading cause of irreversible vision loss worldwide. Screening for DR is recommended to detect sight-threatening complications prior to visual loss. Early Treatment Diabetic Retinopathy Study (ETDRS) seven standard field (7SF) retinal imaging is regarded as the gold standard for DR classification as it provides high-quality fundus images. However, it only captures 34% of retina, and is challenging to adopt in clinical settings due to the need for pupil dilation, photographer training and additional grading time. Therefore, other screening methods are often preferred in clinical practice.

Objectives: To determine whether retinal 7SF imaging still provides the most optimal method in DR screening, or if similar results can be achieved by other methods using a smaller field of view (<7SF) or ultra-wide field (UWF) imaging.

Main findings: Of the total 7,168 articles retrieved from databases and other sources, 16 were included in this review. Of the 16 included articles, seven compared ETDRS 7SF with UWF, five compared ETDRS 7SF with <7SF, and the remaining four used other modalities. Compared to 7SF, retinal images of <7SF and UWF both provided satisfactory performance; however, a higher rate of ungradable images in non-mydriatic <7SF modalities may pose a challenge. In conclusion, considering the time-intensive nature of the 7SF method <7SF and UWF could be reasonable options in DR screening.

Methodology: Two reviewers conducted the searches in PubMed, EMBASE and Cochrane Library to identify relevant studies published from inception to 17 March 2020. No geographical filters were applied. The authors reported identifying one additional record from other sources. The articles published in English were included if they were full-text and peer-reviewed publications on patients at least 18 years old and compared DR classification between two standards (preferably 7SF as one of these). The authors first selected the articles based on the title, then conducted abstract screening and finally full-text screening. Two reviewers screened the identified articles.

Applicability/external validity: Authors mentioned that the gold standard of ETDRS 7SF has stood the test of time in DR grading, but other approaches in general have agreements that can be considered moderate, substantial, or almost perfect. In addition, the authors suggest that solutions should be tailored for individual health care systems considering the population of diabetic patients and health care resources available for DR screening.

Geographic focus:

Included studies in the review were conducted in high income settings only. The authors did not explicitly discuss the applicability of their findings to low and middle income countries (LMICs) in their paper. However, they did mention that screening for diabetic retinopathy (DR) is recommended in LMICs, and that different methods of retinal imaging may have different advantages and disadvantages in these settings.

Summary of quality assessment:

A low confidence was attributed to the conclusions of this review due to the identified limitations in the approach used to conduct it. The authors did not avoid publication and language bias in the review. Also, the authors did not report assessing the risk of bias of included studies and if a rigorous approach was implemented when extracting data of included studies.