
Royal canin is a poor quality food, loaded with grains and many other cheap "fillers". Many of which are causing our pets health problems, including tear staining.
Have you thought of changing to a better quality "Grain" Free product (remembering that RICE is also a grain).
Millies Wolfheart , Eden, Acana, Origen, and quiet a few more. Take care with these good quality products as a lot less is needed when feeding, and can cause a runny tummy.
Of course Raw feeding produces good results and helps with the tear staining.
Feeding raw is no longer bloody and smelly! There are plenty of companies who supply "complete" raw meals and nuggets.