Aim: To review studies of the reliability (reproducibility) of the commonly used methods (ophthalmoscopy and inspection of retinal images) of screening for diabetic retinopathy (DR).
Research design and methods: Literature search.
Results: We found six studies of the intra-examiner agreement after examining the same retinal images. Three of these found an almost perfect agreement (k > 0.8) after inspecting colour slides and digital images; three other studies reported 'significant differences' in microaneurysm counts and only 39-85% agreement rates between two assessments by the same examiner. The inter-examiner agreement was reported in 24 studies. Using stereoscopic photographs, one study found almost perfect agreement after examining seven fields; another study found a substantial to moderate (k = 0.4-0.8) agreement after examining five fields and a third study found a fair agreement (k = 0.2-0.4) after examining a single field. Studies using single- or two-field monoscopic photographs also have reported agreement rates that have varied between almost perfect, substantial and moderate. In four other studies using biomicroscopy, agreement levels varied between perfect and moderate.
Conclusions: Relative to the large number of studies on the validity of the various methods for screening for DR, there are only few studies of their reliability, with a marked variability in their findings. We suggest that future studies of the effectiveness of the various methods for screening for DR should also include data on their reliability.