There are several eyelid disorders in dogs. Entropian (rolling inwards), and ectropian (drooping or rolling outward) are the most common.  Although they are abnormal eyelid conformations, they are characteristic of many breeds. For example, droopy lower eyelids (ectropion) are usually present in Basset hounds and other hound breeds. Shar Peis and Chow Chows, in which breeding selection has been made for numerous facial wrinkles, has led to turning in of the eyelids (both upper and lower in many cases). 

Ectropian, unless very pronounced, does not lead to severe diseases of the eye itself. However, the droopy eyelid may collect debris such as dust, pollen and plant material from the environment. This can cause ocular irritation that leads to watering and a red eye. This is particularly pronounced in hunting dogs or dogs that are outdoors much of the time. Dogs that have ectropion must be watched carefully by their owners for possible foreign bodies in their eyes, and the dogs' eyes must be cleaned and often medicated on a regular basis. Ectropian is also surgically correctable for the health of the dog. 

Entropion on the other hand frequently causes ocular pain and corneal disease. If the eyelid is rolled inward sufficiently so that the hairs of the eyelid rub on the eye, much damage may be done. Dogs with entropion usually squint and have watery eyes. If the entropion is not corrected and the rubbing continues, ulcers often develop on the cornea and the cornea becomes pigmented. Vision may be lost.  

Entropian is a very painful disorder for the dog, requiring delicate surgery to prevent eye damage. With an Entropian eye, the eyelids may roll in as early as 8 - 10 weeks or could roll in between 4 to 6 months, however this can occur even when the dog is a year of age or older. 

Most commonly, Entropian starts as Intermittent Entropian (with the eyelids sometimes positioned normally), advances to Entropian, and requires surgery. Either upper or lower lids may be involved, or a combination of both. Most often both eyes are affected. 

Permanent treatment for entropion requires a surgical procedure to remove a narrow segment of skin and muscle from the eyelid with stitches used to evert the eyelid to a normal position. The sutures are removed in 2 weeks. In breeds where entropion is accompanied by heavy face folds, or in cases where surgery is necessary before a dog is fully mature, it is not unusual for more than one surgical procedure to be required. 

Entropion and ectropion are hereditary disorders in many breeds. But, their mode of inheritance is complex. No one gene controls the development of eyelid conformation. Instead, it is a combination of genes that control eyelid size and shape, depth of the eye socket, size and shape of the eyes, head conformation and amount of facial skin. All of these genes work together to determine the relationship of the eyelids to the eye. 

If an eyelid conformation defect is to be eliminated, only those dogs without entropion or ectropin should be bred.