Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that Figaro has increased brown tear staining from one eye.
Cats naturally have a brown or reddish pigment in their tears, and when the tears overflow onto the face we can see brown staining left behind. The more irritated the eye is the more pigment we tend to see.
Cat with excessive tear staining on their faces may have a blocked or partially blocked tear duct which causes the tears to overflow onto the face rather then go down the tear duct into the nose. This can be something he was born with or secondary to an infection. Your veterinarian may be able to open his tear duct by flushing it open if he has a partial obstruction. Some cats have repeated blocked ducts. Others resolve after having them flushed once.
If the hair around his eyes is long or we have abnormally positioned eyelashes that can cause wicking of his tears onto his face or increased irritation from eyelashes rubbing his eye leading to excessive tearing. You often cannot see the abnormally positioned eyelashes without a bright light and magnifying loop but your veterinarian should be able to see them with their equipment.
The other possibility is that he has entropian, which is a rolling in of his eyelid, or ectropian, which is a saggy eyelid. If he has entropian this will cause his eyelid and eyelashes to rub on his eye leading to increased tearing and thus increased staining.
The dog in the link below has entropian. Notice that the lower lid is rolled and thick whereas the upper lid you can see the eyelashes and it sits neatly against the eye.
If he has ectropian then the lid won't function normally and dust and dirt collect in the eye leading to irritation and increased tearing. The dog in the link below has ectropian. Notice the saggy bottom eyelids that don't fit neatly on the eye.
I understand that these are pictures of dogs, but cats can have similar troubles, we just see them less so there aren't many pictures available to show you.
Some cats suffer from a chronic Herpes infection, which in cats is an upper respiratory viral infection. Herpes virus is easily caught by breathing in virus particles in the air from a sneeze or nasal or eye discharge. In some cats they become a chronic condition leading to nasal congestion that comes and goes or blocked tear dusts from the inflammation.
You can give him an amino acid supplement called L-lysine at a dose of 500mg orally twice daily. If this is caused by a Herpes infection this should help. This amino acid interferes with virus replication and will shorten the infection's duration and severity. Good supplements to try are made by the Viralys brand which comes in a powder to add to the food or a tasty gel. In some cases we need to use topical antiviral drugs in the kitty's affected eye. Your veterinarian can collect a swab sample from his eye and submit it to look for the Herpes virus.
I would have your veterinarian take another look at him and try to determine whether his tear ducts are blocked. In many cases this can be done by putting fluorescein stain into his eyes, adding saline drops and seeing if we get fluorescein stain showing in his nose. If we do that means his nasolacrimal duct is patent.
They can also check for abnormal eyelashes (distichiasis) or whether his eyelids aren't sitting properly against his eye.
And gather a sample to check him for the Herpes virus.
Ideally if your veterinarian is having trouble finding the cause behind his increased tearing you may want to consult with a veterinary ophthalmologist as they will have specialized equipment to visualize his eyes better and the experience of seeing many more cases like your kitty.
In the meantime I recommend using artificial tears several times a day in his affected eye in the lubricant rather then the drop form, to keep his eyes comfortable in case this is related to an eyelid abnormality or misplaced eyelashes. This will cushion his eye so that if he has excess, abnormally positioned eyelashes or entropian (rolled in eyelid) they won't be as irritating and you should see less tears on his face.
If he is rubbing his eye you may also want to place an elizabethan collar on him so he cannot rub his eye/face and cause any further trauma
Please let me know if you have any further questions.