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What is Entropion and explain in detail?
Entropion is a medical condition in which the eyelid (usually the lower lid) folds inward. It is very uncomfortable, as the eyelashes continuously rub against the cornea causing irritation. Entropion is usually caused by genetic factors. This is different from when an extra fold of skin on the lower eyelid causes lashes to turn in towards the eye (epiblepharon). In epiblepharons, the eyelid margin itself is in the correct position, but the extra fold of skin causes the lashes to be misdirected. Entropion can also create secondary pain of the eye (leading to self trauma, scarring of the eyelid, or nerve damage).  The upper or lower eyelid can be involved, and one or both eyes may be affected. When entropion occurs in both eyes, this is known as "bilateral entropion". Repeated cases of trachoma infection may cause scarring of the inner eyelid, which may cause entropion. In human cases, this condition is most common to people over 60 years of age.

Symptoms
Symptoms of entropion include:

Redness and pain around the eye
Sensitivity to light and wind
Sagging skin around the eye
Eye watering
Decreased vision, especially if the cornea is damaged

Causes
Congenital
Aging creating loose skin and stretched and loose ligaments and muscles (senile entropion).
Scarring (mechanical entropion)
Spasm
An eye infection called trachoma is still common in North Africa and South Asia and this can cause scarring of the inner eyelid, which may cause friction and entropion.

Treatment
Treatment is a relatively simple surgery in which excess skin of the outer lids is removed or tendons and muscles are shortened with one or two stitches. General anesthesia is sometimes used before local anesthetics are injected into the muscles around the eye.  Prognosis is excellent if surgery is performed before the cornea is damaged.

Entropion in other species
Entropion has been documented in most dog breeds, although there are some breeds (particularly purebreds) that are more commonly affected than others.  These include the Akita, Pug, Chow Chow, Shar Pei, St. Bernard, Cocker Spaniel, Boxer, English Springer Spaniel, Welsh Springer Spaniel, Labrador Retriever, Cavalier King Charles Spaniel, Neapolitan Mastiff, Bull Mastiff, Great Dane, Irish Setter, Shiba Inu, Rottweiler, Poodle and particularly Bloodhound. The condition is usually present by six months of age