Eye infections are fairly common and can be caused by many things including what has already been offered. If something lodges in the eye. Or when the surface of the eye, called the cornea, gets scratched.
A telltale sign of infection is the appearance of the discharge: It will often be thick, yellow, gray, or green. It may form a crust on the eyelids as well.
Viral infections such as canine adenovirus in dogs can cause runny eyes. Startings out as a watery discharge but then become thicker as the infection progresses.
Some dogs are prone to seasonal allergies, and the only sign may be a clear runny and sometimes sticky eye discharge. Unlike bacterial or viral infections, allergies usually result in a clear discharge.
There is a genetic defect called entropion, in which the eyelid turns inward, causing the lashes to brush against the surface of the eye. Scratching and irritation can become severe. In cats and some breeds of dogs, entropion often affects the lower eyelid. In dogs with big heads and loose facial skin, such as Saint Bernards, shar-peis, and Chow Chows, both lids can be affected. Over time entropion can cause irritation and infection, resulting in a discharge. Sometimes requiring surgical removal of a thin strip of skin containing the hair follicles.
