Entropion is a term that describes inward rotation of either the upper or lower eyelid. Congenital, involutional, acute spastic and cicatricial types exist, but involutional is by far the most common and is associated with aging. Recurrent infections, keratitis, corneal injury and various other problems may arise, which is why an early diagnosis is imperative in reducing the rate of complications. Treatment almost always requires surgery.
Because of constant corneal irritation by inverted eyelashes, patients most often present with persistent ocular discomfort that can be accompanied by redness, pain and a foreign-body sensation in the eye . Additional findings may include ptosis and preseptal swelling of the lower eyelid. The main and most obvious sign is inward rotation of the eyelid, which can be noted without hesitation during physical examination. Recent trauma, eye surgery or infection in the case of cicatricial entropion may be reported. In rare cases, vision may be impaired through reduced visual acuity .
The most important part of the diagnostic workup is a careful and thorough physical examination. Inward rotation of the eyelid should be observed in all patients, especially in the elderly. To support these findings, several tests may be performed. The snap-back test includes traction of the eyelid downward by the physician's hand, after which the eyelid should return to its normal position without the patient blinking. However, patients with entropion will have to blink in order to return the eyelid to its normal position. Additionally, the eyelid laxity test comprises forward pulling of the eyelid and subsequent eyelid dislocation if involution entropion is present . Finally, impaired lower eyelid movement during downward gaze can support the diagnosis .
Surgery is recommended for all patients, and numerous approaches have been described in literature. Repositioning of the anterior lamella, lateral horn-lysis, CO2 laser resurfacing and use of botulinum toxin, while the use of mucosal grafts has also been utilized   . Blepharotomy and rotational sutures also been mentioned as potential approaches, but regardless of the modality, the goal of treatment is to restore the eyelid to its normal position and to abolish corneal irritation by eyelashes . Treatment somewhat depends on the underlying pathogenic mechanism. Anterior lamella reposition, rotational sutures, blepharotomy and lateral horn-lysis are mentioned as strategies for cicatricial entropion management, as is mucosal grafting , while lateral wedge resection and laser resurfacing through the use of CO2 are surgical approaches for involutional forms  .
With successful surgery, entropion has a very good prognosis and minimal recurrence rates are observed. However, if it is left untreated, it may lead to numerous complications, including corneal irritation and ulceration, keratitis, epiphora and even vision loss  . For these reasons, an early diagnosis is detrimental in managing this condition.
Depending on the subtype, entropion arises under different circumstances. Congential entropion can develop as a consequence of epiblepharon, an abnormal skin folding of either upper or lower eyelid with inversion of cilia, or due to eyelid deformities accompanied by trichiasis . Involutional entropion, on the other hand, stems from degenerative changes in eyelid structures as a result of aging. Various pathological changes have been observed, including reduction and degeneration of collagen and elastic fibers , leading to loss of lid support and disinsertion of lower lid retractors, with all changes being age-related . The cause of acute spastic entropion is either ocular surgery or inflammation that causes eyelid edema, leading to extensive contraction of the orbital muscle and consequent inward eyelid rotation . Cicatricial entropion is thought to be a result of chronic irritation of the palpebral conjuctiva .
Studies that were conducted on over 20,000 individuals established a 2.1% prevalence rate of involutional entropion, with a slight predilection toward female gender (1.9% vs 2.4%, respectively) . Aging is the single most important risk factor for the development of involutional entropion, as the main cause is thought to be progressive degeneration of tissues surrounding the eyelid. Senile enophtalmos is also shown to be a risk factor . Similar prevalence rates of true entropion were observed in Japan, but congenital forms were shown to be present in up to 20% of Japanese children less than 1 year old . It is hypothesized that overgrowth of orbicularis muscle is the most important risk factor for congenital entropion, as its enlargement inverts the cillia toward the cornea .
The pathogenesis model somewhat differs across subtypes of entropion. Involutional form starts with degeneration of collagen and elastic fibers, which leads to disruption of normal structural integrity of eyelid structures. Some studies have shows involvement of matrix metalloproteinases (MMPs) that cause upregulation of enzymes that degrade elastic fibers . In addition, various anatomical abnormalities have been established, including thinning of lower lid retractors and canthal tendons, as well as shortened height of the tarsal plate , all creating favorable conditions for inward rotation of the eyelid. On the contrary, cicatricial entropion, which develops as a result of conjuctival scarring, is initiated by some form of trauma or inflammation that leads to eyelid rotation. The underlying mechanism of congenital entropion development, although known to be a result of excessive orbicularis muscle growth, remains unclear.
In the case of entropion, current preventive strategies do not exist and the focus remains on making the diagnosis early on, before the onset of complications. Patients who often experience ocular discomfort and a foreign-body sense should report to their physician for a physical examination that will surely reveal an inverted eyelid.
Entropion denotes an inward rotation of the eyelid which leads to significant irritation to the cornea and predisposes individuals to numerous complications . It is classified into four distinct forms. Involutional, congenital, acute spastic and cicatricial types are described in literature and involutional is by far the most common. In involutional entropion, an entity exclusively seen in older adults, degenerative changes due to aging are thought to be the cause of anatomical dysfunction . Degeneration of collagen fibers, elastosis of tarsal plates and canthal tendos, structures that provide functional stability of the lower eyelid, as well as disinsertion of lower lid retractors are some of the most common pathological changes encountered in these patients  . Enophtalmos, in addition to aging, is also known to be a risk factor . Certain studies estimated an overall prevalence rate of 2.1% in the general population and a slight predilection toward female gender (1.9% vs 2.4%) was observed, but in general, sexes are equally affected. Congenital entropion usually resolves spontaneously within the first 12 months, but other types usually present with progressive eye irritation. Cicatricial forms are typically preceded by either trauma, eye surgery or chronic inflammatory states. Although entropion seems like a benign condition, the eyelashes of the inverted eyelid can cause significant damage to the ocular structures, leading to substantial morbidity that may cause keratitis, corneal abrasion, and loss of vision, which is why it must be diagnosed and treated as soon as possible . Cicatricial entropion often leads to conjuctival scarring, as chronic inflammation is usually present . The diagnosis can be made during physical examination, when inward rotation of the lower eyelid is observed in virtually all cases, while additional tests such as a snap-back probe are useful in solidifying the diagnosis. Surgery is the mainstay of therapy and various approaches exist. Lateral wedge resection, carbon dioxide (CO2) laser resurfacing, reposition of the lamella and a few other techniques are used, depending on the type of entropion and surgeon experience   . Successful surgical treatment leads to excellent outcomes and very low recurrence rates.
Entropion is a term that describes inward rotation of either the upper, but more commonly the lower eyelid and may cause significant discomfort. The end-result is irritation of the cornea by the eyelashes. There are four main subtypes: congenital, involutional, acute spastic and cicatricial. Congenital entropion develops in the first year of life and is thought to be a result of overgrowth of the muscle that surrounds the eye socket, orbicularis oculi. It is established that congenital forms are present in up to 20% of Japanese children, but spontaneous resolution occurs in the vast majority. Involutional entropion is most commonly encountered in medical practice and in this type, eyelid rotation is caused by degenerative changes of collagen and elastic fibers due to aging. Studies have estimated that approximately 2% of the elderly have involutional entropion and these numbers tend to rise with increasing age. Acute spastic entropion is thought to occur as a result of trauma, infection, or prior eye surgery that disrupted normal anatomical architecture of the eyelids, while cicatricial entropion stems from chronic conjuctival changes that lead to scarring. In any case, the main complaint of patients is ocular discomfort and a persistent foreign-body sense. In severe cases, keratitis, excessive tearing, corneal erosions and ulcerations and even vision disturbances may occur, which is why it is important to treat this condition early on. The diagnosis can be made clinically, through a close physical examination that will reveal inward eyelid rotation, while additional tests that evaluate eyelid mobility and stability can be used to support the diagnosis. Treatment almost always requires a surgical approach and many techniques are used, depending on the subtype. Although this condition may seem benign, prolonged irritation of the cornea and other ocular structures may lead to severe morbidity, making early recognition and treatment vital in managing these patients.