Anatomy & Organs

Uvea – structure, function & diseases

Uvea

Uvea is the medical term for the middle part of the eye, which is also known under the term tunica media bulbi . Their name derives from the Latin term for bunch of grapes, which is said to resemble the uvea in dissection.

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 varies from person to person and is also genetically determined. Blue or pale gray or green eyes are the result of a fairly weak pigment count. Strong pigmentation, on the other hand, 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 developed after birth , which explains why babies usually have blue eyes. Inside the eyeball , the uvea lies just below the opaque sclera . In contrast to the inner skin of the eye beneath the uvea, the sclera is highly scattering. The uvea, on the other hand, protects the eye from this scattered radiation. It is penetrated in the rear area by the optic nerve and is open at the front as a pupil

Anatomy & Structure

The middle layer of the eye consists of the iris , the ciliary body and the choroid , which fulfill various tasks in the context of the eye’s function. The tissue itself is comparable to the soft meninges .

Just behind the lens is the iris, often referred to as the iris, which separates the posterior from the anterior chamber of the eye. It consists mainly of blood vessels , smooth muscle cells, the pigment cells and the pupillary opening.

It is followed by the ciliary body surrounded by the ciliary epithelium. The corpus ciliare or radiating body is directly connected to the lens via zonula fibers and can thus ensure a change in the lens curvature by contracting or relaxing its ciliary muscle.

The third component of the uvea is the choroid, medically called the choroid. It surrounds almost the entire vitreous body of the eye and is the most intensively perfused tissue in the human body. Components of the choroid are various vessels, connective tissue cells ( fibrocytes ) and the already mentioned pigment-forming melanocytes. The structural protein collagen is also detectable.

Function & Tasks

The tasks of the three individual elements, iris, ciliary body and choroid, differ and so the uvea can generally not be assigned a specific function.

The main task of the iris is to adjust the pupil and thus control the incidence of light. Like an aperture in photography, the pupil is expanded or contracted with the help of two muscles , thus 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. In times of stress , in the dark or when looking into the distance, the incidence of light is increased by dilating the pupil. However, the pupil contracts when we are tired, in bright surroundings and when looking at things close up.

Two functions are taken over by the ciliary body. On the one hand, it is responsible for the production of aqueous humor . It produces about 2 microliters of water per minute, which initially fills the posterior chamber of the eye. The water then flows into the front chamber, where it washes around the cornea and lens. Both, and also the vitreous, are supplied with nutrients by this water. Furthermore, the eye needs the produced aqueous humor to maintain the intraocular pressure.

The second task of the ciliary body is taken over by its muscle. Through its direct connection with the lens, it controls its precise curvature and allows the visual acuity to be adjusted depending on the distance of the object. The choroid supplies 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 being supplied by the choroid.

Diseases

The possibilities of a disease of the uvea are manifold. They can be congenital or appear over the course of life. In most cases, medical treatment is unavoidable in order to prevent long-term effects, in particular blindness .

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

While uveitis can affect various areas of the uvea, iridocyclitis affects the iris and ciliary bodies. This inflammation is also manifested by pain and blurred vision. 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 uveal melanoma . It develops due to degenerated melanocytes and in many cases is discovered too late or only by chance. However, early detection is important given its tendency to spread widely. The risk of developing the most common eye tumor is highest between the ages of 60 and 70.

A disease of the uvea caused by albinism , which is characterized by a lack of pigment cells, is genetically determined. In the uvea, too, these are completely missing and only the blood vessels of the choroid can be seen in the eye. The eye of an albino, which is also affected by a visual impairment, therefore appears red.

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.