Lower lid ectropion is a common condition in older persons, increasing steadily in incidence with advancing age.
Ectropion is an eversion of the eyelid away from the globe.  It is classified according to its anatomic features as involutional, [2, 3, 4] cicatricial, tarsal, congenital, or neurogenic/paralytic.
Surgical approaches are directed toward the underlying etiologic factors.
Ectropion is an outward turning of the eyelid margin and occurs most often in the lower eyelid. It may be mild or severe and may involve all or part of the eyelid margin. See the image below.
Ectropion is most commonly seen as an involutional change associated with horizontal laxity of the involved eyelid. Ectropion may be subdivided into 5 types: congenital, involutional, cicatricial, paralytic, and mechanical.
Causal factors leading to ectropion include horizontal laxity of the eyelid (universal), dehiscence of the lower eyelid retractors, vertical shortening of the anterior lamella of the eyelid, paralysis of the orbicularis oculi muscle causing loss of eyelid muscular tone, and neoplasia within the lower eyelid pulling or forcing the eyelid away from the globe. 
Presentation is usually either from 1) epiphora (see below), 2) ocular irritation, or 3) cosmesis.
There is generally a progression from eyelid laxity to punctal ectropion, medial ectropion, then generalized ectropion. If the punctum is slightly everted from the lacus lacrimalis, tears cannot effectively drain into the canalicular system. Horizontal eyelid laxity also may produce a flaccid canalicular syndrome or poor lacrimal pump, so that tears are not siphoned from the lacus lacrimalis.
This tearing malfunction is aggravated by the chronic ectropion and eyelid retraction that produce lagophthalmos and secondary exposure keratopathy. With time, the exposed conjunctiva thickens and keratinizes, producing further ocular irritation.
Thorough knowledge of eyelid anatomy is essential to appreciate the etiology and surgical intervention of lower eyelid abnormalities. The eyelid can be conceptualized to consist of an anterior and posterior lamella.
The anterior lamella consists of the skin and orbicularis muscle. The thin delicate skin of the eyelid lacks dermal-like connective tissue and pilosebaceous apparatus that would reduce eyelid mobility. The orbicularis muscle is categorized as either orbital or palpebral portions based on adjacent anatomic structures. Orbital orbicularis muscle overlies the orbital rim. Palpebral orbicularis muscle is further classified as preseptal or pretarsal based on the proximity of orbital septum or tarsus, respectively. At the eyelid margin a strip of orbicularis muscle, the muscle of Riolan, is directly associated with the eyelashes.
The posterior lamella consists of the eyelid retractor, tarsus, and conjunctiva. The lower eyelid is analogous to the upper eyelid with the main variation being the eyelid retractor system. The upper eyelid has a distinct eyelid retractor, the levator muscle, to enhance upper eyelid mobility. The lower eyelid does not have a specialized eyelid retractor. The lower eyelid retractor system originates as a fascia extension of the inferior rectus muscle (capsulopalpebral head). This fascial system splits to encapsulate the inferior oblique muscle and then reunites to form a dense fibrous sheet (capsulopalpebral fascia) to insert onto the inferior tarsal border. The inferior tarsal muscle is a smooth muscle analogous to the superior tarsal muscle (Muller muscle) of the upper eyelid. This muscle originates in the inferior fornical area and extends toward the inferior tarsal border but does not insert on the tarsal border as its counterpart in the upper eyelid does.
The inferior tarsal muscle provides sympathetic innervation to the lower eyelid, and interruption of its innervation results in a slightly elevated position of the lower eyelid margin as observed in Horner syndrome. Otherwise, the inferior tarsal muscle has little pathologic significance. The tarsus provides the primary support or foundation for the eyelids. Although degeneration of the tarsus may promote eyelid laxity, the principle focus of weakness of the eyelids is at the lateral and medial canthal tendons.
The medial canthal tendon has a prominent anterior component firmly connecting the medial canthal angle to the maxillary process of the frontal bone. The posterior limb of the medial canthal tendon provides deep support to the posterior lacrimal crest. The superior branch of the medial canthal tendon also supports the canthal angle. The lateral canthal tendon has contributions from the lateral aspects of the tarsus and the preseptal and pretarsal orbicularis muscle; these insert on the inner aspect of the lateral orbital rim at the Whitnall (lateral orbital) tubercle. Posterior deep insertion of the lateral canthal tendon allows the lateral aspect of the eyelids to approximate the globe.