Conjunctivitis, or pink-eye, is an inflammation of the conjunctiva, the membrane covering the back of the eyelids and the surface of the eyeball up to the cornea. It is a highly contagious viral disease, which ranks among the top most common eye problems in horses. It is spread from horse to horse by direct contact, either via the respiratory route by sneezing and coughing, or by carrier stallions by the venereal route.
The eye membranes appear reddened and somewhat swollen.
Clear, watery discharge from the infected eye.
The horse shows signs of light sensitivity, such as squinting or keeping the eyes closed.
A sticky, purulent discharge develops at the corners of the eye, along with pain and and tenderness to the touch.
Protrusion of the third eyelid develops, in which the eyelid swells across the eye.