Corneal limbus

Last updated

Corneal limbus
Limbus.png
Schematic diagram of the human eye
Details
Identifiers
Latin limbus corneae
MeSH D016850
TA98 A15.2.02.014
TA2 6748
FMA 58342
Anatomical terminology

The corneal limbus (Latin: corneal border) is the border between the cornea and the sclera (the white of the eye). It contains limbal stem cells in its palisades of Vogt. It may be affected by cancer or aniridia (a developmental problem), among other issues. The PS , RV ring is a visible dark ring around the iris of the eye composed of darkened areas of the corneal limbus.

Contents

Structure

The corneal limbus manifests as a dark ring around the iris. Its prominence varies by individual Human eye with limbal ring, anterior view.jpg
The corneal limbus manifests as a dark ring around the iris. Its prominence varies by individual

The corneal limbus is the border between the cornea and the sclera. [1] It is highly vascularised. [1] Its stratified squamous epithelium is continuous with the epithelium covering the cornea. [2]

The corneal limbus contains radially-oriented fibrovascular ridges known as the palisades of Vogt that contain limbal stem cells. [1] [3] The palisades of Vogt are more common in the superior and inferior quadrants around the eye. [4]

Clinical significance

Cancer

The corneal limbus is a common site for the occurrence of corneal epithelial neoplasm.

Aniridia

Aniridia, a developmental anomaly of the iris, disrupts the normal barrier of the cornea to the conjunctival epithelial cells at the limbus.

Calcification

The limbus sign shows dystrophic calcification of the limbus, appearing as an abnormal white color.

Glaucoma treatment

The corneal limbus may be cut to allow for aqueous humour to drain from the anterior chamber of the eye into the subconjunctival space. [5] This can be used in glaucoma treatment. [5] The hole created only needs to be small, although slightly bigger than needed to account for gradual healing. [5] This procedure sometimes fails, particularly if the hole is large. [5] It can lead to eye irritation from blebbing. [5]

Trabeculectomy, a surgery used to treat glaucoma, is best performed with an incision through the superior part of the corneal limbus. [6] Mattress suturing may be used to close this incision. [6]

History

The word "limbus" comes from the Latin meaning "border". [7]

Related Research Articles

<span class="mw-page-title-main">Cornea</span> Transparent front layer of the eye

The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43 dioptres. The cornea can be reshaped by surgical procedures such as LASIK.

<span class="mw-page-title-main">Pterygium (eye)</span> Pinkish, triangular tissue growth on the cornea of the eye

A pterygium of the eye is a pinkish, roughly triangular tissue growth of the conjunctiva onto the cornea of the eye. It typically starts on the cornea near the nose. It may slowly grow but rarely grows so large that it covers the pupil and impairs vision. Often both eyes are involved.

<span class="mw-page-title-main">Eye surgery</span> Surgery performed on the eye or its adnexa

Eye surgery, also known as ophthalmic surgery or ocular surgery, is surgery performed on the eye or its adnexa. Eye surgery is part of ophthalmology and is performed by an ophthalmologist or eye surgeon. The eye is a fragile organ, and requires due care before, during, and after a surgical procedure to minimize or prevent further damage. An eye surgeon is responsible for selecting the appropriate surgical procedure for the patient, and for taking the necessary safety precautions. Mentions of eye surgery can be found in several ancient texts dating back as early as 1800 BC, with cataract treatment starting in the fifth century BC. It continues to be a widely practiced class of surgery, with various techniques having been developed for treating eye problems.

<span class="mw-page-title-main">Refractive surgery</span> Surgery to treat common vision disorders

Refractive surgery is optional eye surgery used to improve the refractive state of the eye and decrease or eliminate dependency on glasses or contact lenses. This can include various methods of surgical remodeling of the cornea (keratomileusis), lens implantation or lens replacement. The most common methods today use excimer lasers to reshape the curvature of the cornea. Refractive eye surgeries are used to treat common vision disorders such as myopia, hyperopia, presbyopia and astigmatism.

<span class="mw-page-title-main">Conjunctiva</span> Part of the eye; protective outer layer covering the sclera

In the anatomy of the eye, the conjunctiva is a thin mucous membrane that lines the inside of the eyelids and covers the sclera. It is composed of non-keratinized, stratified squamous epithelium with goblet cells, stratified columnar epithelium and stratified cuboidal epithelium. The conjunctiva is highly vascularised, with many microvessels easily accessible for imaging studies.

<span class="mw-page-title-main">Phakic intraocular lens</span> Lens implanted in eye in addition to the natural lens

A phakic intraocular lens (PIOL) is an intraocular lens that is implanted surgically into the eye to correct refractive errors without removing the natural lens. Intraocular lenses that are implanted into eyes after the eye's natural lens has been removed during cataract surgery are known as pseudophakic.

<span class="mw-page-title-main">Red eye (medicine)</span> Eye that appears red due to illness or injury

A red eye is an eye that appears red due to illness or injury. It is usually injection and prominence of the superficial blood vessels of the conjunctiva, which may be caused by disorders of these or adjacent structures. Conjunctivitis and subconjunctival hemorrhage are two of the less serious but more common causes.

<span class="mw-page-title-main">Hyphema</span> Hemorrhage in the front chamber of the eye

Hyphema is the medical condition of bleeding in the anterior chamber of the eye between the iris and the cornea. People usually first notice a loss or decrease in vision. The eye may also appear to have a reddish tinge, or it may appear as a small pool of blood at the bottom of the iris in the cornea. A traumatic hyphema is caused by a blow to the eye. A hyphema can also occur spontaneously.

Ocular melanosis (OM) is a blue-gray and/or brown lesion of the conjunctiva that can be separated into benign conjunctival epithelial melanosis (BCEM) and primary acquired melanosis (PAM), of which the latter is considered a risk factor for uveal melanoma. The disease is caused by an increase of melanocytes in the iris, choroid, and surrounding structures. Overproduction of pigment by these cells can block the trabecular meshwork through which fluid drains from the eye. The increased fluid in the eye leads to increased pressure, which can lead to glaucoma. In humans, this is sometimes known as pigment dispersion syndrome.

<span class="mw-page-title-main">Corneal ulcers in animals</span> Veterinary inflammatory condition of the cornea

A corneal ulcer, or ulcerative keratitis, is an inflammatory condition of the cornea involving loss of its outer layer. It is very common in dogs and is sometimes seen in cats. In veterinary medicine, the term corneal ulcer is a generic name for any condition involving the loss of the outer layer of the cornea, and as such is used to describe conditions with both inflammatory and traumatic causes.

<span class="mw-page-title-main">Vernal keratoconjunctivitis</span> Medical condition

Vernal keratoconjunctivitis is a recurrent, bilateral, and self-limiting type of conjunctivitis having a periodic seasonal incidence.

<span class="mw-page-title-main">Pinguecula</span> Medical condition

A pinguecula is a common type of conjunctival stromal degeneration in the eye. It appears as an elevated yellow-white plaque in the bulbar conjunctiva near the limbus. Calcification may also seen occasionally.

<span class="mw-page-title-main">Corneal neovascularization</span> Medical condition

Corneal neovascularization (CNV) is the in-growth of new blood vessels from the pericorneal plexus into avascular corneal tissue as a result of oxygen deprivation. Maintaining avascularity of the corneal stroma is an important aspect of healthy corneal physiology as it is required for corneal transparency and optimal vision. A decrease in corneal transparency causes visual acuity deterioration. Corneal tissue is avascular in nature and the presence of vascularization, which can be deep or superficial, is always pathologically related.

<span class="mw-page-title-main">Corneal ulcer</span> Medical condition of the eye

Corneal ulcer, also called keratitis, is an inflammatory or, more seriously, infective condition of the cornea involving disruption of its epithelial layer with involvement of the corneal stroma. It is a common condition in humans particularly in the tropics and in farming. In developing countries, children afflicted by vitamin A deficiency are at high risk for corneal ulcer and may become blind in both eyes persisting throughout life. In ophthalmology, a corneal ulcer usually refers to having an infection, while the term corneal abrasion refers more to a scratch injury.

A staphyloma is an abnormal protrusion of the uveal tissue through a weak point in the eyeball. The protrusion is generally black in colour, due to the inner layers of the eye. It occurs due to weakening of outer layer of eye by an inflammatory or degenerative condition. It may be of five types, depending on the location on the eyeball.

<span class="mw-page-title-main">Limbal ring</span> Dark ring around the iris of the eye

A limbal ring is a dark ring around the iris of the eye, where the sclera meets the cornea. It is a dark-colored manifestation of the corneal limbus resulting from optical properties of the region. The appearance and visibility of the limbal ring can be negatively affected by a variety of medical conditions concerning the peripheral cornea. It has been suggested that limbal ring thickness may correlate with health or youthfulness and may contribute to facial attractiveness. The thickness of the limbal ring varies by pupil dilation - when the pupil is larger, the limbal ring narrows. Some contact lenses are colored to simulate limbal rings.

Open-globe injuries are full-thickness eye-wall wounds requiring urgent diagnosis and treatment.

<span class="mw-page-title-main">Limbal stem cell</span>

Limbal stem cells, also known as corneal epithelial stem cells, are unipotent stem cells located in the basal epithelial layer of the corneal limbus. They form the border between the cornea and the sclera. Characteristics of limbal stem cells include a slow turnover rate, high proliferative potential, clonogenicity, expression of stem cell markers, as well as the ability to regenerate the entire corneal epithelium. Limbal stem cell proliferation has the role of maintaining the cornea; for example, by replacing cells that are lost via tears. Additionally, these cells also prevent the conjunctival epithelial cells from migrating onto the surface of the cornea.

An artificial iris is an intraocular implant that is used as both a cosmetic and to treat those with aniridia or other eye trauma. People with this condition experience photophobia, or increased sensitivity to light. The artificial iris, made from silicone, acts as a replacement iris. The artificial iris is implanted in the eye using different surgery techniques depending on the patient's eye trauma. Most of the major artificial iris manufacturers are European and the treatment is used sparingly in the United States because of limited FDA approval, in part due to possibility of vision loss and other risks.

Manual small incision cataract surgery (MSICS) is an evolution of extracapsular cataract extraction (ECCE); the lens is removed from the eye through a self-sealing scleral tunnel wound. A well-constructed scleral tunnel is held closed by internal pressure, is watertight, and does not require suturing. The wound is relatively smaller than that in ECCE but is still markedly larger than a phacoemulsification wound. Comparative trials of MSICS against phaco in dense cataracts have found no statistically significant difference in outcomes but MSICS had shorter operating times and significantly lower costs. MSICS has become the method of choice in the developing world because it provides high-quality outcomes with less surgically induced astigmatism than ECCE, no suture-related problems, quick rehabilitation, and fewer post-operative visits. MSICS is easy and fast to learn for the surgeon, cost effective, simple, and applicable to almost all types of cataract.

References

  1. 1 2 3 Dogru, Murat; Chen, Min; Shimmura, Shigeto; Tsubota, Kazuo (2009-01-01), Brightbill, Frederick S.; McDonnell, Peter J.; Farjo, Ayad A.; McGhee, Charles N. J. (eds.), "Chapter 4 - Corneal epithelium and stem cells", Corneal Surgery (Fourth Edition), Edinburgh: Mosby, pp. 25–31, ISBN   978-0-323-04835-4 , retrieved 2021-09-27
  2. Pe'er, Jacob (2007-01-01), Singh, Arun D; Damato, Bertil E.; Pe'er, Jacob; Murphree, A. Linn (eds.), "CHAPTER 23 - Examination techniques, classification, and differential diagnosis of conjunctival and corneal tumors", Clinical Ophthalmic Oncology, Edinburgh: W.B. Saunders, pp. 125–128, ISBN   978-1-4160-3167-3 , retrieved 2021-09-27
  3. Thomas PB, Liu YH, Zhuang FF, Selvam S, Song SW, Smith RE, Trousdale MD, Yiu SC (2007). "Identification of Notch-1 expression in the limbal basal epithelium". Mol. Vis. 13: 337–44. PMC   2633467 . PMID   17392684.
  4. Goldberg MF, Bron AJ (1982). "Limbal palisades of Vogt". Transactions of the American Ophthalmological Society . 80: 155–71. PMC   1312261 . PMID   7182957.
  5. 1 2 3 4 5 Stamper, Robert L; Lieberman, Marc F; Drake, Michael V (2009-01-01), Stamper, Robert L; Lieberman, Marc F; Drake, Michael V (eds.), "CHAPTER 34 - Glaucoma outflow procedures", Becker-Shaffer's Diagnosis and Therapy of the Glaucomas (Eighth Edition), Edinburgh: Mosby, pp. 466–490, ISBN   978-0-323-02394-8 , retrieved 2021-09-27
  6. 1 2 Jackson, Timothy L., ed. (2008-01-01), "Chapter 7 - GLAUCOMA", Moorfields Manual of Ophthalmology, Edinburgh: Mosby, pp. 274–330, doi:10.1016/B978-1-4160-2572-6.50012-5, ISBN   978-1-4160-2572-6 , retrieved 2021-09-27
  7. Iorio, Raffaele; O’Toole, Orna; Pittock, Sean J. (2015-01-01), Zigmond, Michael J.; Rowland, Lewis P.; Coyle, Joseph T. (eds.), "Chapter 29 - Autoimmune and Paraneoplastic Neurological Disorders", Neurobiology of Brain Disorders, San Diego: Academic Press, pp. 467–496, ISBN   978-0-12-398270-4 , retrieved 2021-09-27