Cherry eye in dogs refers to a condition where the gland of the third eyelid, also known as the nictitating membrane, becomes prolapsed or displaced, creating a visible red or pink mass in the corner of the eye. This condition is relatively common in certain breeds and can affect one or both eyes. While not typically painful, it can lead to complications such as dry eye, inflammation, and infection if not treated. Treatment often involves surgical replacement of the gland to its original position to prevent further issues and maintain the dog's eye health.