What causes red, painful eyes in my Shih Tzu? When to see a vet?

Hi there! I am so sorry Simba is not feeling well. From the picture, it looks like the white part of his eye (called the sclera) is very red. There are many reasons why his eye could be red. He could have a corneal ulcer (a scratch on his eye caused my trauma or dry eye), his could have conjunctivitis (inflammation of the tissue around the eye, caused by allergies or bacteria) or glaucoma (high pressure inside the eye) or something systemic causing these issues.

I recommend going to the Emergency Clinic and seeing a veterinarian sooner rather than later if you are worried. Typically, a veterinarian will performed a full physical exam and ophthalmic (eye) exam. This includes a schirmer tear test (to determine if he has dry eye), a fluorescein stain test ( to determine if he has a corneal ulcer), sometimes the vet will check the pressure in the eye too.

I also recommend seeing a vet ASAP if Simba has change in color or texture of the eye, any increase of green or yellow mucus discharge (may indicate infection), an increased pain, holding eye shut or a sudden squirt of clear liquid may indicate a ruptured ulcer. If so, this can be an emergency and should be evaluated at your earliest convenience. You can also start a consultation with, if you would like to talk more about this! Good luck and I hope Simba feels better!