Uvea
Encyclopedia
- For the Pacific island, see Wallis IslandWallis IslandWallis is an island in the Pacific Ocean belonging to the French overseas collectivity of Wallis and Futuna....
.
The uvea (Lat.
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
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
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
. 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
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
and ophthalmology
Ophthalmology
Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...
is relatively modern.
Regions
The vascular middle layer of the eye. It is traditionally divided into 3 areas, from front to back, the irisIris (anatomy)
The iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. "Eye color" is the color of the iris, which can be green, blue, or brown. In some cases it can be hazel , grey, violet, or even pink...
, ciliary body
Ciliary body
The ciliary body is the circumferential tissue inside the eye composed of the ciliary muscle and ciliary processes. It is triangular in horizontal section and is coated by a double layer, the ciliary epithelium. This epithelium produces the aqueous humor. The inner layer is transparent and covers...
, and choroid
Choroid
The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye, containing connective tissue, and lying between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye , while in the outlying areas it narrows to 0.1 mm...
.
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 not fully opaque.
In addition some uveal regions have special functions of great importance, including secretion of the aqueous humour by the ciliary processes
Ciliary processes
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.-Anatomy:...
, control of accommodation
Accommodation reflex
The accommodation reflex is a reflex action of the eye, in response to focusing on a near object, then looking at distant object , comprising coordinated changes in vergence, lens shape and pupil size...
(focus) by the ciliary body, and optimisation of retinal illumination by the iris's control over the pupil
Pupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
. Many of these functions are under the control of the autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
.
Pharmacology
The pupil provides a visible example of the neural feedback control in the body. This is subserved by a balance between the antagonistic sympatheticSympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
and parasympathetic
Parasympathetic nervous system
The parasympathetic nervous system is one of the two main divisions of the autonomic nervous system . The ANS is responsible for regulation of internal organs and glands, which occurs unconsciously...
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
Pupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
, uveitis
Uveitis
Uveitis specifically refers to inflammation of the middle layer of the eye, termed the "uvea" but in common usage may refer to any inflammatory process involving the interior of the eye....
, 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 ophthalmiaSympathetic ophthalmia
Sympathetic ophthalmia is a granulomatous uveitis of both eyes following trauma to one eye. It can leave the patient completely blind. Symptoms may develop from days to several years after a penetrating eye injury. See also the reviews by Damico et al. , Chu and Foster , and Friedlaender et al...
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 uveitisUveitis
Uveitis specifically refers to inflammation of the middle layer of the eye, termed the "uvea" but in common usage may refer to any inflammatory process involving the interior of the eye....
, choroiditis
Choroiditis
Choroiditis is a condition where the choroid is inflamed.When it presents in combination with retinitis , the condition is known as chorioretinitis....
, iritis
Iritis
Iritis is a form of anterior uveitis and refers to the inflammation of the iris of the eye.-Types:There are two main types of iritis: acute and chronic. They differ in numerous ways....
, Iridocyclitis
Iridocyclitis
Iridocyclitis, a type of anterior uveitis, is a condition in which the uvea of the eye is inflamed.Iridocyclitis isInflammation of the iris and the ciliary body.- Symptoms :Symptoms include:* Photophobia* Redness* Watering of the eyes* Lacrimation...
, anterior uveitis, sympathetic ophthalmia
Sympathetic ophthalmia
Sympathetic ophthalmia is a granulomatous uveitis of both eyes following trauma to one eye. It can leave the patient completely blind. Symptoms may develop from days to several years after a penetrating eye injury. See also the reviews by Damico et al. , Chu and Foster , and Friedlaender et al...
, uveal melanoma
Uveal melanoma
Uveal melanoma is a cancer of the eye involving the iris, ciliary body, or choroid . Tumors arise from the pigment cells that reside within the uvea giving color to the eye...
.