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Uvea
Gray869.png
Horizontal section of the eyeball. (Iris labeled at top, ciliary body labeled at upper right, and choroid labeled at center right.)
Schematic diagram of the human eye en.svg
Schematic diagram of the human eye.
Latin tunica vasculosa bulbi
MeSH Uvea
For the Pacific island, see Wallis Island.

The uvea (Lat. uva, grape), also called the uveal layer, uveal coat, uveal tract, or vascular tunic, is the pigmented middle of the three concentric layers that make up an eye. The name is possibly a reference to its reddish-blue or almost black colour, wrinkled appearance and grape-like size and shape when stripped intact from a cadaveric eye. Its use as a technical term in anatomy and ophthalmology is relatively modern.

Contents

Anatomy

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Regions

The uvea lies between the corneosclera (outermost layer of the eye) and the retina (innermost layer/in the back of the eye). It is traditionally divided into 3 or 4 regions, from front to back, the iris, ciliary body, pars plana and choroid. These distinctions are based on their different structures as seen under light microscopy, and continued use of these terms is appropriate in anatomical studies. For clinical use, the terms anterior uvea (ie, iris and ciliary body) and posterior uvea (ie, choroid) are now in common use, since diseases often spread beyond a single anatomical region of the uvea.

Histology

In general the uvea consists of a pigmented, highly vascular loose fibrous tissue. The pigment is produced and held in numerous dendritic melanocytes, similar to normal dermal melanocytes. The blood vessels show patterns which are specific to the region of the uvea, and are described in more detail under iris, ciliary body, pars plana and choroid. The stroma also contains large nerves, which are branches of the posterior ciliary nerves. They enter the eye around the optic nerve, and run forwards in the uvea to reach their termination in the cilary body or iris.

External and internal relations

These are described in more detail under the anatomic regions, as above.

Broadly, the outer aspect of the posterior uvea lies directly against the sclera, but at the root of the iris, the uvea is reflected sharply towards the central axis, so that its outer surface becomes the anterior surface of the iris, which is in contact only with the aqueous humour.

The inner aspect of the posterior uvea lies against Bruch's membrane, which separates it from the retina. On passing forwards beyond the ora serrata, Bruch's membrane and the retina are no longer present, and the inner relation of the uvea is a continuous epithelial sheet, represented in turn by the pars plana epithelium, the ciliary epithelium and the iris pigment epithelium.

Physiology

The prime functions of the uveal tract as a unit are:

1. nutrition and gas exchange. Uveal vessels directly perfuse the ciliary body and iris, to support their metabolic needs, and indirectly supply diffusible nutrients to the outer retina, cornea & lens, which lack any intrinsic blood supply.

2. light absorption. The uvea improves the contrast of the retinal image by reducing reflected light within the eye (analogous to the black paint inside a camera), and also absorbs outside light transmitted through the sclera, which is by no means opaque.

In addition, some uveal regions have special functions of great importance, particularly secretion of the aqueous humour by the ciliary processes, control of accommodation (focus) by the ciliary body, and optimisation of retinal illumination by the iris's control over the pupil. Many of these functions are under the control of the autonomic nervous system.

Pharmacology

The pupil provides a visible example of the neural feedback control in the body. This is subserved by a balance between the antagonistic sympathetic and parasympathetic divisions of the autonomic nervous system. Informal pharmacological experiments have been performed on the pupil for centuries, since the pupil is readily visible, and its size can be readily altered by drugs, even crude plant extracts, applied to the cornea. Pharmacological control over pupil size continues to be an important part of the treatment of some ocular diseases - see pupil, uveitis, acute glaucoma, chronic glaucoma.

The metabolically-active process of secreting aqueous humour can also be reduced by drugs, which is important in treating both acute and chronic glaucoma.

Immunology

The normal uvea consists of immune competent cells, particularly lymphocytes, and is prone to respond to inflammation by developing lymphocytic infiltrates. A rare disease called sympathetic ophthalmia may represent 'cross-reaction' between the uveal and retinal antigens (ie, the body's inability to distinguish between them, with resulting misdirected inflammatory reactions).

Pathology

See uveitis, choroiditis, iritis, anterior uveitis, sympathetic ophthalmia, uveal melanoma.

External links


Travel guide

Up to date as of January 14, 2010
(Redirected to Wallis and Futuna article)

From Wikitravel

Oceania : Wallis and Futuna
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Flag
Image:wf-flag.png
Quick Facts
Capital Mata-Utu
Currency Change Franc Pacifique (XPF)
Area 274 sq km
Population 15,585 (July 2002 est.)
Language French, Wallisian (indigenous Polynesian language)
Religion Roman Catholic 99%, other 1%
Calling Code 681
Internet TLD .wf

Wallis and Futuna is an overseas community of France consisting of two small island groupings in Polynesia, near Fiji and Samoa.

Wallis and Futuna comprises two archipelagoes:

Hoorn Islands group (also known as the Futuna Islands, and as Îles Horne)

Alofi Island is the smaller of the two. According to legend it was as densely inhabited as Futuna up until the 19th century, when the Futuna people slaughtered and ate the population in a single raid.

Wallis Islands group (also known as ʻUvea, as is Wallis Island)

Wallis Island is surrounded by 15 smaller islands, all of which are uninhabited.

  • Mata-Utu (Matāʻutu) - capital of Wallis and Futuna, also capital of Hahake District, on Wallis Island
  • Leava - the capital of the Sigavé chiefdom, and the third largest village on Futuna Island

Understand

Although discovered by the Dutch and the British in the 17th and 18th centuries, it was the French who declared a protectorate over the islands in 1842. In 1959, the inhabitants of the islands voted to become a French overseas territory. There are still three ceremonial kingdoms within the territory: Alo, Sigave, Wallis.

The islands are volcanic in origin, with low hills, and fringing reefs. The highest point is Mont Singavi, at 765 m. The climate is tropical: hot, rainy season (November to April); cool, dry season (May to October); rains 2,500-3,000 mm per year (80% humidity); average temperature 26.6 degrees C.

Get in

By plane

Uvea and Futuna each have an airport. only airline that flies to wallis futuna is aircalin

By boat

The port of Mata-Utu is located on Uvea. Leava (Sigave) is on Futuna.

Get around

Uvea has 120 km of roads, much of which is paved. All the main villages on Futuna can be accessed on paved but rough roads.

Buy

Costs

Banking facilities are limited, with no bank located on Futuna. Also, the BWF bank in Wallis will not directly change US $100 bills. Travelers are advised to do their currency exchanges in Noumea, New Caledonia or Nadi, Fiji prior to arrival.

  • Hôtel ALBATROS, route du collége mataotamaVillage Mala'e, +681721827.  edit
  • Hôtel MOANA-HOU, route du bord de mer Village liku Districte hahakeBP 136 Mata-Utu, +681722135.  edit
  • Hôtel Restaurant LOMIPEAU, Standard route territoriale n°1 Village aka'aka District hahake BP 84 Mata-Utu, +681722021.  edit
  • Hôtel Restaurant Le Fia-Fia, lieut-dit Puilata Village nuku Royaume sigave BP 28 Sigave, +681723245.  edit
  • SOMALAMA PARK HOTEL, lieut-dit somalama Village tavai Royaume sigave BP 2 Sigave, +681723120.  edit
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