One of the most common eye problems in dogs is conjunctivitis or pink eye.

Symptoms include redness accompanied by discharge, which can be one of three types: clear (in what’s called serous conjunctivitis), mucuslike (mucoid conjunctivitis) or puslike (purulent conjunctivitis).

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Serous conjunctivitis is caused by irritants such as allergens, wind, cold and dust. Mucoid conjunctivitis occurs when small mucous glands on the underside of your dog’s third eyelid react to irritants by forming a rough, discharge-producing surface.

Purulent conjunctivitis is a case of serous conjunctivitis that has become infected, usually by bacteria such as Streptococcus or Staphylococcus.