Uvea

Information about Uvea

Latintunica vasculosa bulbi
MeSH Uvea
Dorlands/Elsevier t_22/12832415
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 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.

Anatomy

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, 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. These parts of the uvea also contain smooth muscle.

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 the neatest and most 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 contains 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

 •  • [ e]
Sensory system - Visual system - Eye
Fibrous tunic (outer)Conjunctiva • Sclera  • Schlemm's canal • Trabecular meshwork • Limbus
Cornea (Epithelium, Bowman's, Stroma, Descemet's, Endothelium)
Uvea (middle)Choroid (Ciliary processes, Choriocapillaris, Bruch's membrane) • Iris (Stroma)  • Pupil • Ciliary body
Retina (inner)Macula • Fovea • Optic disc
Anterior segmentAnterior chamber • Aqueous humour • Posterior chamber • Lens
Posterior segmentVitreous humour • Zonular fibers • Zonule of Zinn
Latin}}} 
Official status
Official language of: Vatican City
Used for official purposes, but not spoken in everyday speech
Regulated by: Opus Fundatum Latinitas
Roman Catholic Church
Language codes
ISO 639-1: la
ISO 639-2: lat
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Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. Created and updated by the United States National Library of Medicine (NLM), it is used by the MEDLINE/PubMed
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Elsevier, the world's largest publisher of medical and scientific literature, forms part of the Reed Elsevier group. Based in Amsterdam, the company has substantial operations in the UK, USA and elsewhere.
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Wallis (Polynesian: ʻUvea) is an island in the Pacific Ocean belonging to the French overseas collectivity (collectivité d'outre-mer, or COM) of Wallis and Futuna.
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Latin}}} 
Official status
Official language of: Vatican City
Used for official purposes, but not spoken in everyday speech
Regulated by: Opus Fundatum Latinitas
Roman Catholic Church
Language codes
ISO 639-1: la
ISO 639-2: lat
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Eyes are organs of vision that detect light. Different kinds of light-sensitive organs are found in a variety of organisms. The simplest eyes do nothing but detect whether the surroundings are light or dark, while more complex eyes can distinguish shapes and colors.
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Anatomy (from the Greek ἀνατομία anatomia, from ἀνατέμνειν
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Ophthalmology is the branch of medicine which deals with the diseases and surgery of the visual pathways, including the eye, brain, and areas surrounding the eye, such as the lacrimal system and eyelids.
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The sclera and cornea form the fibrous tunic of the bulb of the eye; the sclera is opaque, and constitutes the posterior five-sixths of the tunic; the cornea is transparent, and forms the anterior sixth.
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For the moth genus, see Retina (moth).


The retina is a thin layer of neural cells that lines the back of the eyeball of vertebrates and some cephalopods. It is comparable to the film in a camera.
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In anatomy, the iris (plural irises or irides) is the most visible part of the eye of vertebrates, including humans. The following describes the iris of vertebrates, not the independently evolved iris found in some cephalopods.
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The ciliary body is the circumferential tissue inside the eye composed of the ciliary muscle and ciliary processes.[1] It is part of the uveal tract—the layer of tissue which provides most of the nutrients in the eye.
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The pars plana is part of the uvea, choroidea, one of the three layers that comprise the eye. It is about 4 mm long and located near the point where the iris and sclera touch.
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The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye lying between the retina and the sclera, with a thickness about 0.5 mm. The choroid provides oxygen and nourishment to the outer layers of the retina [1] .
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Melanocytes are cells located in the bottom layer (the stratum basale) of the skin's epidermis and in the middle layer of the eye (the uvea).

Melanogenesis

Through a process called melanogenesis
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In anatomy, the iris (plural irises or irides) is the most visible part of the eye of vertebrates, including humans. The following describes the iris of vertebrates, not the independently evolved iris found in some cephalopods.
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The ciliary body is the circumferential tissue inside the eye composed of the ciliary muscle and ciliary processes.[1] It is part of the uveal tract—the layer of tissue which provides most of the nutrients in the eye.
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The pars plana is part of the uvea, choroidea, one of the three layers that comprise the eye. It is about 4 mm long and located near the point where the iris and sclera touch.
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The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye lying between the retina and the sclera, with a thickness about 0.5 mm. The choroid provides oxygen and nourishment to the outer layers of the retina [1] .
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Optic Nerve may be a reference to:
  • Optic nerve, the anatomical structure;
  • Optic Nerve (comic), the comic book series;
  • Optic Nerve (1998), the seminal release from the Irish hip hop act known as Exile Eye; or

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aqueous humour is a thick watery substance that is located in the eye.

Locations

The anterior segment is the front third of the eye that includes the structures in front of the vitreous humour: the cornea, iris, ciliary body, and lens.
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Bruch's membrane is the innermost layer of the choroid. It is also called the vitreous lamina, because of its glassy microscopic appearance. It is 2–4 μm thick.
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The ora serrata is the serrated junction between the retina and the ciliary body. This junction marks the transition from the simple non-photosensitive area of the retina to the complex, multi-layered photosensitive region.
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The pars plana is part of the uvea, choroidea, one of the three layers that comprise the eye. It is about 4 mm long and located near the point where the iris and sclera touch.
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Main article: iris (anatomy)

Anatomy

The iris pigment epithelium (IPE) is a two-cell thick layer of cuboidal cells lying behind the iris.
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The ciliary processes are formed by the inward folding of the various layers of the choroid, i.e., the choroid proper and the lamina basalis, and are received between corresponding foldings of the suspensory ligament of the lens.
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The accommodation reflex is a reflex action of the eye, in response to focusing on a near object, then looking at distant object (and vice versa), comprising coordinated changes in vergence, lens shape and pupil size.
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The pupil (Latin pupilla "little doll" > pupa "doll") is the variable-sized, black circular or slit shaped opening in the center of the iris that regulates the amount of light that enters the eye.
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autonomic nervous system (ANS) (or visceral nervous system) is the part of the peripheral nervous system that acts as a control system, maintaining homeostasis in the body. These maintenance activities are primarily performed without conscious control or sensation.
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The Sympathetic Nervous System (SNS) is a branch of the autonomic nervous system. It is always active at a basal level (called sympathetic tone) and becomes more active during times of stress.
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