There didn’t seem to be any associated pain or infection but it was a bit unsightly and the owner asked if the eyes could be checked out.

This grey and somewhat gloopy discharge from the eyes is a relatively common finding in horses, especially in middle-aged or elderly animals. It is actually composed of tears. The pink tissue (conjunctiva) that lines the eyelids and socket contain lacrimal glands that produce tears constantly. These tears are spread across the surface of the eye (the cornea) every time the horse blinks.