There are several comments about the accuracy of the algorithm, but Doctors also struggle with diagnosis. In the Deep Mind study on DR they found that for about 20% of referable cases doctors disagreed on the diagnosis about 40-50% of the time. In order to combat this they had at least 3 and up to 7 opthamologists grade each image.
Source: https://jamanetwork.com/journals/jama/fullarticle/2588763