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Ectropion
The supporting structure of the lower eyelid may be likened to a hammock, with a cartilage-like central stiffener element (tarsal plate) attached by two tendons to the bone on either side of the eye. If the tendons become stretched due to wear-and-tear or from trauma or even other surgery, the lid may lose its normal adherence to the eye surface and sag outward, a condition known as ectropion.
Wind and dust may dry out and irritate the delicate tissue lining the back of the exposed lid. Tearing develops when the tear duct opening on the edge of the eyelid falls away and can no longer pick up the moisture. Eventually the eye may develop scarring.
Ectropion surgery is designed to tighten the stretched tendons. However, if the tendons have become too shredded, an entirely new means of support must be fashioned by borrowing from the remaining healthy tissues.
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Ectropion - before
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Ectropion - after
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Entopion
Like ectropion, entropion develops from a weakening of eyelid support system. In addition, the tendon-like sheath below the tarsal plate tears, thus allowing an unstable eyelid to rotate inward against the eye. Pain from the lashes and skin rubbing against the cornea can be severe, and the risk of entropion to vision is immediate.
Surgical correction on entropion entails rotating the lid margin back to a more normal position by tightening both the canthal tendons and the tendon-like sheath. Less commonly, entropion affects the upper eyelid; grafting of tissue from donor sources is generally required.
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Entropion - before
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Entropion - after
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Eyelid Retraction
Eyelid retraction, like ectropion, is caused by a compromised support system but also by the shrinkage of any of several eyelid layers (skin, muscle, retractors). This combination of horizontal laxity and vertical shortening causes the eyelid to pull downward (retract) below the cornea, thereby exposing the white of the eye. Lid retraction can occur naturually, with thryoid disease, or as a consequence of overdone surgery (as shown below).
In addition to tendon reinforcement, grafting of cartilage and/or skin may be necessary.
Lid retraction associated with thyroid disease is related to overactive eyelid muscles; corrective techniques are directed at lessening their pull.
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