Uvea

Uvea is the medical name of the middle skin of the eye, also under the term Tunica media bulbi is common. Its name is derived from the Latin term for grape, which the uvea is said to resemble during preparation.

What is the uvea?

The uvea is the pigment-bearing layer of the eye and is therefore responsible for the different eye colors. This depends on the strength of the pigmentation, which differs from person to person and is also genetically determined. Blue or pale gray or green eyes are the result of a very low pigment count. A heavy pigmentation, however, makes the eyes appear brown.

The pigment-forming cells themselves, the so-called melanocytes, are only a few micrometers in size. They are only fully trained after birth, which explains the mostly blue eyes of babies. Inside the eyeball, the uvea lies directly under the opaque sclera, the sclera. In contrast to the inner eye skin lying under the uvea, the dermis is highly scattering. The uvea, on the other hand, protects the eye from this scattered radiation. It is penetrated by the optic nerve in the rear and is open as a pupil on the front

Anatomy & structure

The middle skin of the eye is made up of the iris, the ciliary body and the choroid, which perform various tasks within the framework of the eye function. The tissue itself is comparable to the soft meninges.

The iris, also known as the iris, is located directly behind the lens and separates the anterior and posterior chambers of the eye. It mainly consists of blood vessels, smooth muscle cells, pigment cells and the pupil opening.

The ciliary body, framed by the ciliary epithelium, adjoins them. The corpus ciliary or radiation body is connected directly to the lens via zonular fibers and can thus change the curvature of the lens by contraction or relaxation of its ciliary muscle.

The third component of the uvea is the choroid, medically called the choroid. It surrounds almost the entire vitreous humor of the eye and is the tissue with the most intensive blood supply in the human body. Components of the choroid are various vessels, connective tissue cells (fibrocytes) and the pigment-forming melanocytes mentioned above. The structural protein collagen can also be detected.

Function & tasks

The tasks of the three individual elements, iris, ciliary body and choroid, differ and so generally no specific function can be assigned to the uvea.

The main task of the iris is to adjust the pupil and thus control the incidence of light. Like an aperture when taking a picture, the pupil is widened or contracted with the help of two muscles, thereby increasing or reducing the incidence of light. The movement of the two muscles is controlled by the autonomic nervous system. Deliberate activation is not possible. During stress, in the dark or looking into the distance, the widening of the pupil increases the incidence of light. The pupil contracts when you are tired, in bright surroundings or when you are close-up.

The ciliary body takes on two functions. On the one hand, he is responsible for the production of aqueous humor. It produces around 2 microliters of water per minute, which initially fills the posterior chamber. The water then flows into the anterior chamber and washes around the cornea and lens. Both, and also the vitreous body, are supplied with nutrients from this water. The eye also needs the aqueous humor it produces to maintain intraocular pressure.

The second task of the ciliary body is performed by its muscle. Due to its direct connection with the lens, it controls its precise curvature and enables the visual acuity to be adjusted depending on the distance to the object. The choroid provides the underlying retina with the oxygen and nutrients it needs. As part of the central nervous system, this layer of nerve cells is dependent on the supply of the choroid.

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Diseases

The possibilities of a disease of the uvea are manifold. They can be congenital as well as occur in the course of life. Medical treatment is usually unavoidable in order to prevent long-term effects, particularly blindness.

A common inflammation is uveitis. The disease, popularly known as iris inflammation, manifests itself through pain, reddened eyes, sensitivity to light and reduced visual acuity. Because of these symptoms, there is a risk of confusion with conjunctivitis. Treatment is usually done with an ointment containing cortisone.

While various areas of the uvea can be affected in uveitis, iridocyclitis affects the iris and ciliary body. This inflammation also manifests itself in pain and visual disturbances. In addition, sluggish pupillary reactions and changes in eye color are common. Iridocyclitis caused by viruses or certain rheumatic diseases can lead to glaucoma or cataracts.

One of the most serious diseases is the choroidal melanoma. It occurs due to degenerate melanocytes and in many cases is discovered too late or only by chance. However, early detection is important in view of its tendency to vary widely. The risk of the occurrence of the most common eye tumor is highest between the ages of 60 and 70.

A genetic disease of the uvea is caused by albinism, which is characterized by a lack of pigment cells. These are also completely absent in the uvea and so only the blood vessels of the choroid can be seen in the eye. The eye of an albino who is also visually impaired therefore appears red.