Many conditions can impact the position of the eyelid relative to the eyeball. These malpositions can cause decreased vision because the eyelid blocks vision or irritation to the eyelid surface because of increased exposure and irritation.
Upper Eyelid Malpositons
There are four basic eyelid malpositions of the upper eyelid: drooping down of the upper eyelid (upper lid ptosis); retraction of the upper eyelid; inturning of the eyelid and lash line (entropion) and out turning of the eyelid (ectropion).
Upper Eyelid Ptosis
Weakeness in the nerve to the muscle of the upper eyelid, stretching or disinsertion of the muscle into the lid, or weakness of the muscles of the upper eyelid can cause the lid to lower. There is a congenital form in which there is poor development of the upper eyelid muscle that causes the lid to droop. Ptosis surgery involves shortening and reinserting the eyelid muscle into the eyelid. If the ptosis is severe, the muscles of the eyebrow may be attached to the eyelid to help elevate the lid.
Eyelid retraction is caused when the muscle is overactive or inflammation and scarring cause it to tighten and pull the eyes more open than normal. This frequently causes a surprised appearance and irritation of the eye surface because of drying. It is frequently seen in patients with thyroid eye disease.
Entropion (inturning of the eyelids) causes the lash line and external skin of the eyelid to turn inward and rub against the surface of the eye. This frequently causes an irritation and redness to the eye and needs surgical correction.
With aging, the eyelids can also become very lax and this can cause the lower eyelid to sag and turn outward. Dryness of the eye surface is irritating and can cause chronic red eyes. Eyelid surgery generally involves tightening of the eyelids and repositioning them to the correct height. This condition is more common on the lower eyelid.