Cherry eye refers to a prolapsed nictitating membrane.

Dogs have three eyelids. The third eyelid is the nictitating membrane. It supplies nutrients and oxygen to the eye through tear production. 

Once the fibrous attachment becomes weak and breaks, the tear gland moves more freely and causes irritation in the gland even more.  This irritation leads to swelling and will eventually form the red/pink swollen mass.

Brachycephalic breeds are most likely to experience issues with their nictitating membrane, hence the common cases of cherry eyes in Bulldogs. 

So be sure to keep a lookout for both eyes if you know your Bully has an issue with one eye. 

Sometimes, cherry eye can correct itself, but the more swollen and irritated it becomes, the more difficult it is to correct.  Contact your vet early. 

Here is the good news: There are several options for successful treatment which include surgical and non-surgical procedures depending on the severity of the ailment. 

One surgical procedure is to replace the third eyelid gland. Replacement of the gland will greatly reduce the risk to “dry eye” later in life, and tear production should remain similar.

Or your vet might opt for the  “pocketing method,” which requires suturing of tissue around the prolapse and encasing it in a layer of conjunctiva. 

Removal of the gland (old standard)  is not recommended because it reduces tear production in the eye which leads to dry eyes.