Eyelid

An eyelid is a thin fold of skin that covers and protects the human eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. The human eyelid features a row of eyelashes along the eyelid margin, which serve to heighten the protection of the eye from dust and foreign debris, as well as from perspiration. "Palpebral" (and "blepharal") means relating to the eyelids. Its key function is to regularly spread the tears and other secretions on the eye surface to keep it moist, since the cornea must be continuously moist. They keep the eyes from drying out when asleep. Moreover, the blink reflex protects the eye from foreign bodies.

Eyelid
Eye makeup
Upper and lower eyelids
Details
Arterylacrimal, superior palpebral, inferior palpebral
Nerveupper: infratrochlear, supratrochlear, supraorbital, lacrimal
lower: infratrochlear, branches of infraorbital
Identifiers
LatinPalpebra
(palpebra inferior, palpebra superior)
MeSHD005143
TAA15.2.07.024
FMA54437 75178, 54437
Anatomical terminology

Structure

Layers

The eyelid is made up of several layers; from superficial to deep, these are: skin, subcutaneous tissue, orbicularis oculi, orbital septum and tarsal plates, and palpebral conjunctiva. The meibomian glands lie within the eyelid and secrete the lipid part of the tear film.

Skin

The skin is similar to areas elsewhere, but is relatively thin[1] and has more pigment cells. In diseased persons these may wander and cause a discoloration of the lids. It contains sweat glands and hairs, the latter becoming eyelashes as the border of the eyelid is met.[2] The skin of the eyelid contains the greatest concentration of sebaceous glands found anywhere in the body.[1]

Nerve supply

In humans, the sensory nerve supply to the upper eyelids is from the infratrochlear, supratrochlear, supraorbital and the lacrimal nerves from the ophthalmic branch (V1) of the trigeminal nerve (CN V). The skin of the lower eyelid is supplied by branches of the infratrochlear at the medial angle, the rest is supplied by branches of the infraorbital nerve of the maxillary branch (V2) of the trigeminal nerve.

Blood supply

In humans, the eyelids are supplied with blood by two arches on each upper and lower lid. The arches are formed by anastomoses of the lateral palpebral arteries and medial palpebral arteries, branching off from the lacrimal artery and ophthalmic artery, respectively.

Function

The human eyelid features a row of eyelashes along the eyelid margin, which serve to heighten the protection of the eye from dust and foreign debris.

Clinical significance

Any condition that affects the eyelid is called eyelid disorder. The most common eyelid disorders, their causes, symptoms and treatments are the following:

  • Hordeolum (stye) is an infection of the sebaceous glands of Zeis usually caused by Staphylococcus aureus bacteria, similar to the more common condition Acne vulgaris. It is characterized by an acute onset of symptoms and it appears similar to a red bump placed underneath the eyelid. The main symptoms of styes include pain, redness of the eyelid and sometimes swollen eyelids. Styes usually disappear within a week without treatment. Otherwise, antibiotics may be prescribed and home remedies such as warm water compresses may be used to promote faster healing. Styes are normally harmless and do not cause long lasting damage.
  • Chalazion (plural: chalazia) is caused by the obstruction of the oil glands and can occur in both upper and lower eyelids. Chalazia may be mistaken for styes due to the similar symptoms. This condition is however less painful and it tends to be chronic. Chalazia heal within a few months if treatment is administered and otherwise they can resorb within two years. Chalazia that do not respond to topical medication are usually treated with surgery as a last resort.
  • Blepharitis is the irritation of the lid margin, where eyelashes join the eyelid. This is a common condition that causes inflammation of the eyelids and which is quite difficult to manage because it tends to recur.[3] This condition is mainly caused by staphylococcus infection and scalp dandruff. Blepharitis symptoms include burning sensation, the feeling that there is something in the eye, excessive tearing, blurred vision, redness of the eye, light sensitivity, red and swollen eyelids, dry eye and sometimes crusting of the eyelashes on awakening. Treatment normally consists in maintaining a good hygiene of the eye and holding warm compresses on the affected eyelid to remove the crusts. Gently scrubbing the eyelid with the warm compress is recommended as it eases the healing process. In more serious cases, antibiotics may be prescribed.
  • Demodex mites are a genus of tiny mites that live as commensals in and around the hair follicles of numerous mammals including humans, cats and dogs. Human demodex mites typically live in the follicles of the eyebrows and eyelashes. While normally harmless, human demodex mites can sometimes cause irritation of the skin (demodicosis) in persons with weakened immune systems.
  • Entropion usually results from aging, but sometimes can be due to a congenital defect, a spastic eyelid muscle, or a scar on the inside of the lid that could be from surgery, injury, or disease.[4] It is an asymptomatic condition that can, rarely, lead to trichiasis, which requires surgery. It mostly affects the lower lid, and is characterized by the turning inward of the lid, toward the globe.
  • Ectropion is another aging-related eyelid condition that may lead to chronic eye irritation and scarring. It may also be the result of allergies and its main symptoms are pain, excessive tearing and hardening of the eyelid conjunctiva.
  • Laxity is also another aging-related eyelid condition that can lead to dryness and irritation. Surgery may be necessary to repair the eyelid to its natural position. In certain instances, excessive lower lid laxity creates the Fornix of Reiss – a pocket between the lower eyelid and globe – which is the ideal location to administer topical ophthalmic medications.
  • Eyelid edema is a condition in which the eyelids are swollen and tissues contain excess fluid. It may affect eye function when it increases the intraocular pressure. Eyelid edema is caused by allergy, trichiasis or infections.[5] The main symptoms are swollen red eyelids, pain, and itching. Chronic eyelid edema can lead to blepharochalasis.
  • Eyelid tumors may also occur. Basal cell carcinomas are the most frequently encountered kind of cancer affecting the eyelid, making up 85% to 95% of all malignant eyelid tumors.[6] The tumors may be benign or malignant. Usually benign tumors are localized and removed before becoming a cancerous threat and before they become large enough to impair vision. Malignant tumors on the other hand tend to spread to surrounding areas and tissues.
  • Blepharospasm (eyelid twitching) is an involuntary spasm of the eyelid muscle. The most common factors that make the muscle in the eyelid twitch are fatigue, stress, and caffeine.[7] Eyelid twitching is not considered a harmful condition and therefore there is no treatment available. Patients are however advised to get more sleep and drink less caffeine.
  • Eyelid dermatitis is the inflammation of the eyelid skin. It is mostly a result of allergies or contact dermatitis of the eyelid. Symptoms include dry and flaky skin on the eyelids and swollen eyelids. The affected eyelid may itch. Treatment consists in proper eye hygiene and avoiding the allergens that trigger the condition. In rare cases, topical creams may be used but only under a doctor's supervision.
  • Ptosis (drooping eyelid) is when the upper eyelid droops or sags due to weakness or paralysis of the levator muscle (responsible for raising the eyelid), or due to damage to nerves controlling the muscle. It can be a manifestation of the normal aging process, a congenital condition, or due to an injury or disease. Risk factors related to ptosis include diabetes, stroke, Horner syndrome, Bell's Palsy (compression/damage to Facial nerve), myasthenia gravis, brain tumor or other cancers that can affect nerve or muscle function.
  • Ablepharia (ablepharon) Congenital absence of or reduction in the size of the eyelids.[8]

Surgery

The eyelid surgeries are called blepharoplasties and are performed either for medical reasons or to alter one's facial appearance.

Most of the cosmetic eyelid surgeries are aimed to enhance the look of the face and to boost self-confidence by restoring a youthful eyelid appearance. They are intended to remove fat and excess skin that may be found on the eyelids after a certain age.

Eyelid surgeries are also performed to improve peripheral vision or to treat chalazion, eyelid tumors, ptosis, extropion, trichiasis, and other eyelid-related conditions.

Eyelid surgeries are overall safe procedures but they carry certain risks since the area on which the operation is performed is so close to the eye.

Society and culture

Eyelid enhancement

Blepharoplasty is a cosmetic surgical procedure performed to correct deformities and improve or modify the appearance of the eyelids.[9] With 1.43 million people undergoing the procedure in 2014,[10] blepharoplasty is the second most popular cosmetic procedure in the world (Botulinum toxin injection is first), and the most frequently performed cosmetic surgical procedure in the world.[11]

The procedure is particularly popular in East Asia, where it has been reported to be the most common aesthetic procedure in Taiwan and South Korea.[12] Though the procedure is also used to reinforce muscle and tendon tissues surrounding the eye, the operative goal of East Asian blepharoplasty is to remove the adipose and linear tissues underneath and surrounding the eyelids in order to crease the upper eyelid.[13]

The use of double sided tape to create the illusion of creased, or "double" eyelids has become a prominent practice in China and other Asian countries. There is a social pressure for women to have this surgery, and also to use the alternative (taping) practices.[14] Blepharoplasty has become a common surgical operation that is actively encouraged, whilst other kinds of plastic surgery are actively discouraged in Chinese culture.[15]

Death

After death, it is common in many cultures to pull the eyelids of the deceased down to close the eyes. This is a typical part of the last offices.

See also

Stye02
Eyelid affected by stye

Additional images

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Bloodvessels of the eyelids, front view

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Horizontal section through the eye of an eighteen days' embryo rabbit. X 30

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Sagittal section of right orbital cavity

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Sagittal section through the upper eyelid

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The tarsi and their ligaments. Right eye; front view

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The lacrimal apparatus. Right side

Slide2www

Extrinsic eye muscle. Nerves of orbita. Deep dissection

References

  1. ^ a b Goldman, Lee. Goldman's Cecil Medicine (24th ed.). Philadelphia: Elsevier Saunders. p. 2426. ISBN 1437727883.
  2. ^ "eye, human." Encyclopædia Britannica. Encyclopædia Britannica Ultimate Reference Suite. Chicago: Encyclopædia Britannica, 2010.
  3. ^ "Facts About Blepharitis". Retrieved 30 March 2010.
  4. ^ "Eyelid Disorders". Retrieved 30 March 2010.
  5. ^ "Upper Eyelid Edema Treatment and Symptoms". Retrieved 30 March 2010.
  6. ^ "Eyelid and Orbital Tumors". Retrieved 30 March 2010. "Eyelid and Orbital Tumours". Retrieved 22 August 2014.
  7. ^ "Eyelid twitch". Retrieved 30 March 2010.
  8. ^ Taber's Cyclopedic Medical Dictionary, Edition 21, Page-6.
  9. ^ American Society of Plastic Surgeons. Web. http://www.plasticsurgery.org/cosmetic-procedures/eyelid-surgery.html
  10. ^ Taylor, Rosie. "July 2015 ISAPS Global Statistics Release." International Society of Aesthetic Plastic Surgery (2015): n. pag. Web. 8 Jul 2015. http://www.isaps.org/Media/Default/global-statistics/July%202015%20ISAPS%20Global%20Statistics%20Release%20-%20Final.pdf
  11. ^ "Quick Facts: Highlights of the ISAPS 2014 Statistics on Cosmetic Surgery." International Society of Aesthetic Plastic Surgery (2015). Web. http://www.isaps.org/Media/Default/global-statistics/Quick%20Facts%202015v2.pdf
  12. ^ Liao WC, Tung TC, Tsai TR, Wang CY, Lin CH (2005). "Celebrity arcade suture blepharoplasty for double eyelid". Aesthetic Plastic Surgery. 29 (6): 540–5. doi:10.1007/s00266-005-0012-5. PMID 16237581.
  13. ^ Mayo Clinic Staff. "Blepharoplasty." Mayo Clinic (2016). Web. 27 Apr 2016. http://www.mayoclinic.org/tests-procedures/blepharoplasty/basics/definition/prc-20020042
  14. ^ Levinovitz, Alan (22 October 2013). "Chairman Mao Invented Traditional Chinese Medicine". Slate (magazine). Retrieved 2 July 2016
  15. ^ Cornell, Joanna. "In the Eyelids of the Beholder." Yale Globalist (2010): n. pag. Web. 2 Mar 2011. http://tyglobalist.org/perspectives/in-the-eyelids-of-the-beholder/

Sources

Blepharitis

Blepharitis ( BLEF-ər-EYE-tis) is one of the most common ocular conditions characterized by inflammation, scaling, reddening, and crusting of the eyelid. This condition may also cause burning, itching, or a grainy sensation when introducing foreign objects or substances to the eye. Although blepharitis is not sight-threatening, it can lead to permanent alterations of the eyelid margin. The overall etiology is a result of bacteria and inflammation from congested meibomian oil glands at the base of each eyelash. Other conditions may give rise to blepharitis, whether they be infectious or noninfectious, including, but not limited to, bacterial infections or allergies.

Different variations of blepharitis can be classified as seborrheic, staphylococcal, mixed, posterior or meibomitis, or parasitic. In a survey of US ophthalmologists and optometrists, 37% to 47% of patients seen by those surveyed had signs of blepharitis, which can affect all ages and ethnic groups. One single-center study of 90 patients with chronic blepharitis found that the average age of patients was 50 years old.

Blepharochalasis

Blepharochalasis is an inflammation of the eyelid that is characterized by exacerbations and remissions of eyelid edema, which results in a stretching and subsequent atrophy of the eyelid tissue, leading to the formation of redundant folds over the lid margins. It typically affects only the upper eyelids, and may be unilateral as well as bilateral.

Blepharophimosis

Blepharophimosis is a congenital condition characterized by a horizontally narrow palpebral fissure. It is also part of a syndrome blepharophimosis, ptosis, and epicanthus inversus syndrome, also called blepharophimosis syndrome, which is a condition where the patient has bilateral ptosis with reduced lid size, vertically and horizontally. The nasal bridge is flat and there is hypoplastic orbital rim. Both the vertical and horizontal palpebral fissures (eyelid opening) are shortened; the eyes are also spaced more widely apart than usual, also known as telecanthus.

Vignes (1889) probably first described this entity, a dysplasia of the eyelids. There are two known types of blepharophimosis, type 1 and type 2. Although research is limited, it is known that type 1 and 2 are expressed with the same symptoms mentioned above, but type 1 also has the characteristic of premature ovarian insufficiency (POI) in women, which causes menopausal symptoms in patients as young as 15 years old. This is due to the shortening of the FOXL2 gene.

Blepharoplasty

Blepharoplasty (Greek: blepharon, "eyelid" + plassein "to form") is the plastic surgery operation for correcting defects, deformities, and disfigurations of the eyelids; and for aesthetically modifying the eye region of the face. With the excision and the removal, or the repositioning (or both) of excess tissues, such as skin and adipocyte fat, and the reinforcement of the corresponding muscle and tendon tissues, the blepharoplasty procedure resolves functional and cosmetic problems of the periorbita, which is the area from the eyebrow to the upper portion of the cheek. The procedure is more common among women, who accounted for approximately 85% of blepharoplasty procedures in 2014 in the USA and 88% of such procedures in the UK.The operative goals of a blepharoplastic procedure are the restoration of the correct functioning to the affected eyelid(s) and the restoration of the aesthetics of the eye-region of the face, which are achieved by eliminating excess skin from the eyelid(s), smoothing the underlying eye muscles, tightening the supporting structures, and resecting and re-draping the excess fat of the retroseptal area of the eye, in order to produce a smooth anatomic transition from the lower eyelid to the cheek.

In an eye surgery procedure, the usual correction or modification (or both) is of the upper and the lower eyelids, and of the surrounding tissues of the eyebrows, the upper nasal-bridge area, and the upper portions of the cheeks, which are achieved by modifying the periosteal coverings of the facial bones that form the orbit (eye socket). The periosteum comprises two-layer connective tissues that cover the bones of the human body:

the external layer of networks of dense, connective tissues with blood vessels, and

the internal, deep layer of collagenous bundles composed of spindle-shaped cells of connective tissue, and a network of thin, elastic fibres.The Oriental blepharoplasty procedure differs from the classic blepharoplasty. In younger patients the goal of the surgery is to create a supratarsal fold ("double eyelid surgery") whereas in older patients the goals are to create or elevate the supratarsal fold and to resect surplus eyelid skin ("Asian bleparoplasty").

Blepharospasm

Blepharospasm is any abnormal contraction or twitch of the eyelid. The condition should be distinguished from the more common, and milder, involuntary quivering of an eyelid, known as myokymia. In most cases, blepharospasm symptoms last for a few days and then disappear without treatment, but in some cases the twitching is chronic and persistent, causing life-long challenges. In these cases, the symptoms are often severe enough to result in functional blindness. The person's eyelids feel like they are clamping shut and will not open without great effort. People have normal eyes, but for periods of time are effectively blind due to their inability to open their eyelids. In contrast, the reflex blepharospasm is due to any pain in and around the eye.

It is of two types: essential and reflex blepharospasm. The benign essential blepharospasm is a focal dystonia—a neurological movement disorder involving involuntary and sustained contractions of the muscles around the eyes. The term essential indicates that the cause is unknown, but fatigue, stress, or an irritant are possible contributing factors. Blepharospasm is sometimes part of benign fasciculation syndrome.

Although there is no cure, botulinum toxin injections may help temporarily. A surgical procedure known as myectomy may also be useful. It is a fairly rare disease, affecting only one in every 20,000 people in the United States. The word is from Greek: βλέφαρον / blepharon, eyelid, and σπασμός / spasmos, spasm, an uncontrolled muscle contraction.

Chalazion

Chalazion is a cyst in the eyelid due to a blocked oil gland. They are typically in the middle of the eyelid, red, and non painful. They tend to come on gradually over a few weeks.A chalazion may occur following a stye or from hardened oils blocking the gland. The blocked gland is usually the meibomian gland but can also be the gland of Zeis. A stye and cellulitis may appear similar. A stye, however, is usually more sudden in onset, painful, and occurs at the edge of the eyelid. Cellulitis is also typically painful.Treatment is initiated with warm compresses. If this is not effective injecting steroids into the lesion may be tried. If large, incision and drainage may be recommended. While relatively common the frequency of the condition is unknown. The term is from the Greek "khalazion" meaning "small hailstone".

Dacryoadenitis

Dacryoadenitis is inflammation of the lacrimal glands (the tear-producing glands).

Dacryocystitis

Dacryocystitis is an infection of the lacrimal sac, secondary to obstruction of the nasolacrimal duct at the junction of lacrimal sac. The term derives from the Greek dákryon (tear), cysta (sac), and -itis (inflammation). It causes pain, redness, and swelling over the inner aspect of the lower eyelid and epiphora. When nasolacrimal duct obstruction is secondary to a congenital barrier it is referred to as dacrocystocele. It is most commonly caused by Staphylococcus aureus and Streptococcus pneumoniae. The most common complication is corneal ulceration, frequently in association with S. pneumoniae. The mainstays of treatment are oral antibiotics, warm compresses, and relief of nasolacrimal duct obstruction by dacryocystorhinostomy.

East Asian blepharoplasty

East Asian blepharoplasty, also known as "double eyelid surgery", is a type of cosmetic surgery where the skin around the eye is reshaped (blepharoplasty). The purpose of the procedure is to create an upper eyelid with a crease (i.e. "double eyelid") from an eyelid that is naturally without a crease (also known as a "single eyelid" or "monolid").Anatomically, there are a number of subtle differences in the upper eyelids of East Asians, compared with the eyelids of Europeans and Sub-Saharan Africans. While some East Asians have a double eyelid and some do not, there is also a large variation in the crease position (double eyelid size) of the East Asian upper eyelid. The upper lid fold can range from 1 mm (0.039 in) above the eyelash line to about 10 mm (0.39 in). Several methods can be used to create the double eyelid — including the full-incisional, partial incision and no incision methods (e.g. the DST method). Each has its advantages depending on the patient's anatomy and desires.

East Asian blepharoplasty have been reported to be the most common aesthetic procedure in Taiwan, South Korea and other parts of East Asia and is also frequently performed in Northeast Indian states such as Assam. The procedure has been reported to have some risk of complications, but is generally quite safe if done by an expert plastic surgeon. Practitioners of East Asian blepharoplasty include plastic surgeons (facial plastic and reconstructive surgeons), otolaryngologists, oral and maxillofacial surgeons, and ophthalmologists (oculoplastic surgeons). A procedure to remove the epicanthal fold (i.e. an epicanthoplasty) is often performed in conjunction with an East Asian blepharoplasty.The procedure to alter the natural East Asian "single eyelid" appearance has been a subject of controversy. For example, opponents of the procedure described it as being "indoctrinated by white standards of beauty", although New York-based cosmetic surgeon Dr. Edward Kwan states that many patients who get the procedure done are "not trying to look white", but look like the many East Asians who naturally have an eyelid fold. There is also a belief that double eyelids provide a more energetic appearance, and the procedure is popular among high school graduates in China with the view that it will improve their job prospects.

Ectropion

Ectropion is a medical condition in which the lower eyelid turns outwards. It is one of the notable aspects of newborns exhibiting congenital Harlequin-type ichthyosis, but ectropion can occur due to any weakening of tissue of the lower eyelid. The condition can be repaired surgically. Ectropion is also found in dogs as a genetic disorder in certain breeds.

Entropion

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.

Eyelid dermatitis

Eyelid dermatitis is commonly related to atopic dermatitis or allergic contact dermatitis. Volatile substances, tosylamide, epoxy hardeners, insect sprays, and lemon peel oil may be implicated, with many cases of eyelid contact dermatitis being caused by substances transferred by the hands to the eyelids.

Eyelid glue

Eyelid glue, commonly called eye putti (アイプチ, ai puchi), is a type of eye make-up used in East Asia designed to change the monolid (eyelid without a crease). Eyelid glue is a water-soluble adhesive that is easy to remove.

Lagophthalmos

Lagophthalmos is the inability to close the eyelids completely.Blinking covers the eye with a thin layer of tear fluid, thereby promoting a moist environment necessary for the cells of the exterior part of the eye. The tears also flush out foreign bodies and wash them away. This is crucial to maintain lubrication and proper eye health. If this process is impaired, as in lagophthalmos, the eye can suffer abrasions and infections. Lagopthalmos leads to corneal drying and ulceration.

Levator palpebrae superioris muscle

The levator palpebrae superioris (Latin for: elevating muscle of upper eyelid) is the muscle in the orbit that elevates the superior (upper) eyelid.

Nictitating membrane

The nictitating membrane (from Latin nictare, to blink) is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the medial canthus for protection and to moisten it while maintaining vision. Some reptiles, birds, and sharks have full nictitating membranes; in many mammals, a small, vestigial portion of the membrane remains in the corner of the eye. Some mammals, such as camels, polar bears, seals and aardvarks, have full nictitating membranes. Often called a third eyelid or haw, it may be referred to in scientific terminology as the plica semilunaris, membrana nictitans, or palpebra tertia.

Ptosis (eyelid)

Ptosis is a drooping or falling of the upper eyelid. The drooping may be worse after being awake longer when the individual's muscles are tired. This condition is sometimes called "lazy eye," but that term normally refers to the condition amblyopia. If severe enough and left untreated, the drooping eyelid can cause other conditions, such as amblyopia or astigmatism. This is why it is especially important for this disorder to be treated in children at a young age, before it can interfere with vision development.

The term is from Greek πτῶσις "a fall, falling."

Stye

A stye, also known as a hordeolum, is a bacterial infection of an oil gland in the eyelid. This results in a red tender bump at the edge of the eyelid. The outside or the inside of the eyelid can be affected.The cause of a stye is usually a bacterial infection by Staphylococcus aureus. The internal ones are due to infection of the meibomian gland while the external ones are due to an infection of the gland of Zeis. A chalazion on the other hand is a blocked oil gland without infection. They are typically in the middle of the eyelid and not painful.Often a stye will go away without any specific treatment in a few days or weeks. Recommendations to speed improvement include warm compresses. Occasionally antibiotic eye ointment may be recommended. While these measures are often recommended, evidence to support them is poor. The frequency at which styes occur is unclear. They may happen at any age.

Trichiasis

Trichiasis ( trik-ee-AY-sis, tri-KEYE-ə-sis) a medical term for abnormally positioned eyelashes that grow back toward the eye, touching the cornea or conjunctiva. This can be caused by infection, inflammation, autoimmune conditions, congenital defects, eyelid agenesis and trauma such as burns or eyelid injury. It is the leading cause of infectious blindness in the world.Standard treatment involves removal or destruction of the affected eyelashes with electrology, specialized laser, or surgery. In many cases, removal of the affected eyelashes with forceps resolves the symptoms, although the problem often recurs in a few weeks when the eyelashes regrow. Severe cases may cause scarring of the cornea and lead to vision loss if untreated. Mild cases may not require treatment.

Repeated cases of trachoma infection may cause trichiasis.Posterior misdirection of normal lashes most frequently affects lower lid.

The orbit of the eye
Bones
Muscles
Eyelid
Lacrimal apparatus
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