Risk stratification for diabetic eye screening. Reply to Stratton I. M. and Aldington S. J. (letter)

To the Editor : We thank Drs Stratton and Aldington for their comments on our paper. Our manuscript [1] was in the late stages of review at the time of the publication of their paper [2]. We fully acknowledge as stated in our discussion that apparent regression of retinopathy can result from a variety of causes including true regression of disease, changes in the retina that are not captured in retinal photographs and inaccuracy of the actual grading. However, as also noted in our discussion, whenwe constrainedmodels to allow onlymisclassification and no actual regression, the model fit was not as good as when the model allowed for both misclassification and regression, so we do not think the regression noted in the paper is principally a result of issues with grading. As stated in our paper [1], the Scottish Diabetic Retinopathy Screening (DRS) programme has a centralised quality controlled grading system. This is comprised of grading centres all working to a single grading scheme with robust internal and external quality assurance. A high standard of quality controlled grading is essential for any screening programme. We embrace this, and have published data documenting our quality assurance results [3], as cited in our