Secondly, watch out for eye staining problems! (animalso.com)
There are also eye stain removers that you sprinkle directly into your pet's food. (dog-supplies-advisor.com)
An easy test to see if there is a blocked nasal - lacrimal duct is to use a fluorescein eye stain and wait to see if it leaks out of your guinea pig's nose. (thesprucepets.com)