Entropion is defined as rolling in of the eyelid. The lower eyelid is most commonly affected and is frequently seen in breeds such as the Bulldog, Shar Pei, and Chow. Because abnormal eyelid conformation can lead to irritation of the ocular surface, including corneal ulceration, surgery to correct the entropion is the treatment of choice.
The photo below shows the left eye of a dog with entropion before (left) and after (right) surgery. Note that the eyelid margin is not visible in the left photo and is normal in the right photo (yellow arrow).