Name = PAGENAME
Latin = tunica vasculosa bulbi
Caption = Horizontal section of the eyeball. (Iris labeled at top,
ciliary bodylabeled at upper right, and choroidlabeled at center right.)
Caption2 = Schematic diagram of the human eye.
MeshName = Uvea
MeshNumber = A09.371.894
DorlandsPre = t_22
DorlandsSuf = 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 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 anatomyand ophthalmologyis relatively modern.
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 planaand 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.
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 planaand 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
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 planaepithelium, the ciliary epitheliumand the iris pigment epithelium.
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.
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
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 ophthalmiamay represent 'cross-reaction' between the uveal and retinal antigens(ie, the body's inability to distinguish between them, with resulting misdirected inflammatory reactions).
uveitis, choroiditis, iritis, anterior uveitis, sympathetic ophthalmia, uveal melanoma.
* [http://www.visionweb.com/content/consumers/dev_consumerarticles.jsp?RID=37 Diagram at visionweb.com]
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Look at other dictionaries:
Uvea — Uvéa Pour l’article homophone, voir Ouvéa. Royaume coutumier d’Uvéa … Wikipédia en Français
úvea — f. anat. Túnica vascular del globo ocular que comprende la coroides, el iris y el cuerpo ciliar. Medical Dictionary. 2011. úvea epitelio pos … Diccionario médico
Uvéa — la plus importante des îles qui forment le TOM (français) de Wallis et Futuna; 96 km²; moins de 10 000 hab. Cette île volcanique et la vingtaine d îlots qui l entourent forment les îles Wallis. Le roi d Uvéa jouit d une autorité coutumière … Encyclopédie Universelle
uvea — 1520s, from medical L. uvea, from L. uva grape; uvula (see UVULA (Cf. uvula)) … Etymology dictionary
uvea — uvèa ž <G mn uvéā> DEFINICIJA anat. srednja očna ovojnica, sastoji se od irisa, koroide i cilijarnog tijela ETIMOLOGIJA srlat. ≃ lat. uva: grozd … Hrvatski jezični portal
úvea — (De uva). f. Anat. túnica úvea … Diccionario de la lengua española
Uvea — U ve*a, n. [NL., fr. L. uva grape.] (Anat.) The posterior pigmented layer of the iris; sometimes applied to the whole iris together with the choroid coat. [1913 Webster] … The Collaborative International Dictionary of English
Uvĕa — (lat.), die Traubenhaut, s.u. Auge 1) … Pierer's Universal-Lexikon
Uvēa — Uvēa, polynes. Inselgruppe, s. Uea … Meyers Großes Konversations-Lexikon
Uvĕa — (neulat.), die Traubenhaut, s. Text zur Tafel »Auge des Menschen« … Meyers Großes Konversations-Lexikon
Uvéa — Uvéa, 1) eine der Loyaltyinseln, Neukaledonien. 2) Hauptinsel der Wallisinseln des französischen Überseeterritoriums Wallis und Futuna … Universal-Lexikon