If there isn't any diabetic retinopathy, you would code either E11.9, along with the appropriate Z codes for use of oral hypoglycemics and/or insulin, or E10.9, since you said the cataracts are age related.
As far as the training goes, why don't you just make a list of the diabetic retinopathy codes and hypertensive retinopathy codes, along with their individual explanations. The doctors should be specifying the level of either in the medical records and the coders can select the appropriate codes from the list you provide.
There is also a west coast practice which does an excellent annual list of eye ICD-10 codes. Google Pacific Cataract and Laser Institute and the list is available for free download. I believe it's under "Resources."
Tom Cheezum, O.D., CPC, COPC