HOME

TheInfoList




The uvea (;
Lat.
Lat.
''uva'', "grape"), also called the ''uveal layer'', ''uveal coat'', ''uveal tract'', ''vascular tunic'' or ''vascular layer'' is the pigmented middle of the three concentric layers that make up an
eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light L ...

eye
.


History and etymology

The originally medieval Latin term comes from the Latin word ''uva'' ("grape") and is a reference to its grape-like appearance (reddish-blue or almost black colour, wrinkled appearance and grape-like size and shape when stripped intact from a cadaveric eye). In fact, it is a partial loan translation of the Ancient Greek term for the
choroid The choroid, also known as the choroidea or choroid coat, is the Blood vessel, vascular layer of the eye, containing connective tissues, and lying between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye ...
, which literally means “covering resembling a grape”. Its use as a technical term for part of the eye is ancient, but it only referred to the choroid in Middle English and before.
/ref>


Structure


Regions

The uvea is the vascular middle layer of the eye. It is traditionally divided into three areas, from front to back, the: * Iris *
Ciliary body The ciliary body is a part of the eye that includes the ciliary muscle, which controls the shape of the lens, and the ciliary epithelium, which produces the aqueous humor. The aqueous humor is produced in the non-pigmented portion of the cilia ...
*
Choroid The choroid, also known as the choroidea or choroid coat, is the Blood vessel, vascular layer of the eye, containing connective tissues, and lying between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye ...


Function

The prime functions of the uveal tract as a unit are: * 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, sclera, and lens, which lack any intrinsic blood supply. (The cornea has no adjacent blood vessels and is oxygenated by direct gas exchange with the environment.) * 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 not fully opaque. In addition, some uveal regions have special functions of great importance, including secretion of the aqueous humour by the
ciliary processes The ciliary processes are formed by the inward folding of the various layers of the choroid, viz. the choroid proper and the Lamina basalis choroideae, lamina basalis, and are received between corresponding foldings of the suspensory ligament of ...
, control of accommodation (focus) by the ciliary body, and optimisation of retinal illumination by the iris's control over the
pupil The pupil is a black hole located in the center of the iris of the eye Eyes are organs of the visual system The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photore ...

pupil
. Many of these functions are under the control of the
autonomic nervous system The autonomic nervous system (ANS), formerly the vegetative nervous system, is a division of the peripheral nervous system that supplies smooth muscle and glands, and thus influences the function of viscera, internal organs. The autonomic nervous ...

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 The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The autonomic nervous system is responsible for regulating t ...
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 applying drugs—even crude plant extracts—to the cornea. Pharmacological control over pupil size remains an important part of the treatment of some ocular diseases. Drugs can also reduce the metabolically active process of secreting aqueous humour, which is important in treating both acute and chronic
glaucoma Glaucoma is a group of eye diseases which result in damage to the optic nerve The optic nerve, also known as cranial nerve II, or simply as CN II, is a paired cranial nerve Cranial nerves are the nerve A nerve is an enclosed, cable-li ...

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 Sympathetic ophthalmia (SO), also called spared eye injury, is a diffuse granuloma A granuloma is an aggregation of macrophages that forms in response to chronic inflammation Inflammation (from la, inflammatio) is part of the complex biologic ...
may represent 'cross-reaction' between the uveal and retinal
antigens In immunology Immunology is a branch of biology that covers the study of immune systems in all organisms. Immunology charts, measures, and contextualizes the Physiology, physiological functioning of the immune system in states of both health ...
(i.e., the body's inability to distinguish between them, with resulting misdirected inflammatory reactions).


Clinical significance

See
uveitis Uveitis () is the inflammation of the uvea, the pigmented layer that lies between the inner retina and the outer fibrous layer composed of the sclera and cornea. The uvea consists of the middle layer of pigmented vascular structures of the eye and ...
,
choroiditis Chorioretinitis is an inflammation of the choroid (thin pigmented vascular coat of the eye) and retina of the eye. It is a form of posterior uveitis. If only the choroid is inflamed, not the retina, the condition is termed choroiditis. The ophthalmo ...
,
iritis Uveitis () is the inflammation of the uvea The uvea (; Lat. ''uva'', "grape"), also called the ''uveal layer'', ''uveal coat'', ''uveal tract'', ''vascular tunic'' or ''vascular layer'' is the pigmented middle of the three concentric layers ...

iritis
,
iridocyclitis Uveitis () is the inflammation of the uvea The uvea (; Lat. ''uva'', "grape"), also called the ''uveal layer'', ''uveal coat'', ''uveal tract'', ''vascular tunic'' or ''vascular layer'' is the pigmented middle of the three concentric layers th ...
,
anterior uveitis Uveitis (pronounced ''oo-vee-eye-tis'') is the inflammation of the uvea, the pigmented layer that lies between the inner retina and the outer fibrous layer composed of the sclera and cornea. The uvea consists of the middle layer of pigmented vascu ...
,
sympathetic ophthalmia Sympathetic ophthalmia (SO), also called spared eye injury, is a diffuse granuloma A granuloma is an aggregation of macrophages that forms in response to chronic inflammation Inflammation (from la, inflammatio) is part of the complex biologic ...
, and
uveal melanoma Uveal melanoma is a cancer (melanoma Melanoma, also redundantly known as malignant melanoma, is a type of skin cancer Skin cancers are cancers that arise from the skin Skin is the layer of usually soft, flexible outer tissue covering the ...
.


References


External links

*
Diagram at visionweb.com
{{Authority control Human eye anatomy