Note

EDITOR,--Undoubtedly, diabetic retinopathy remains an important cause of preventable blindness, but Bob Ryder's statement that ophthalmoscopy alone will miss up to two thirds of sight threatening cases is misleading. 1 In support of this view Ryder quotes our study of 1983 among others, but he misquotes our results. 2 In our study the sensitivity of detection of any form of retinopathy, including background retinopathy, was close to 100%, but the specificity for the identification of sight threatening retinopathy was lower, with a rate of false positive results of 24% and a rate of false negative results of 3-4%--that is, a quarter of patients diagnosed as having sight threatening retinopathy were found on further investigation not to have it.