It can be caused by a physical irritant to the eye, which would not be contagious.
Here are the different types:
Serous conjunctivitis is a mild condition in which the membranes look pink and somewhat swollen. The discharge is clear and watery. Serous conjunctivitis is caused by physical irritants such as wind, cold, dust, and various allergens such as those that cause allergic blepharitis. Allergic conjunctivitis is often accompanied by
itching, and the dog will rub his face. Some viral agents will cause a clear discharge as well.
Follicular (mucoid) conjunctivitis is a condition in which the small mucous glands (follicles) on the underside of the
nictitating membrane react to an eye
irritant or infection by forming a rough, cobblestone surface that irritates the eye and produces a mucoid discharge. After the inciting factor has been treated, the follicles may persist and the rough surface acts as a chronic irritant.
Purulent conjunctivitis is serous conjunctivitis that becomes infected. The usual culprits are the bacteria Streptococcus and Staphylococcus. The conjunctiva is red and swollen. The eye discharge contains mucus and
pus. Thick secretions may crust the eyelids.