Choroid
Synonyms in a broader sense
Vascular skin (uvea)
Medical: Choroid
English: choroid
introduction
The choroid (Choroid) is the rear part of the vascular skin (Uvea) of the eye. It is embedded between the retina and the dermis as a middle shell. The vascular skin also includes the iris and the ciliary body (Corpus ciliary). With its network of blood vessels, it serves to nourish neighboring structures in the eye and itself consists of three layers. Since the choroid does not carry any sensitive nerve fibers, pain always indicates an involvement of neighboring structures provided with sensitive nerve fibers.
The blood flow through the choroid is the strongest in the entire human body.
Structure of the choroid
The choroid belongs to the vascular skin, also called the middle skin of the eye (Uvea). In addition to the choroid, it includes the rainbow skin and the ciliary body. It lies between the retina (retina) and the dermis (Sclera).
The choroid consists of the following four layers from the inside out:
- Lamina basalis (Link with retina)
- Lamina choroidocapillaris (small capillaries)
- Lamina vasculosa (large arteries)
- Lamina suprachoroidea (Link with dermis)
Function of the choroid
The choroid (Choroid) has several functions: It contains many blood vessels and thus ensures the supply of parts of the eyeball (Bulbus oculi) with oxygen and nutrients that cells need to survive. In particular, the outer layer of the retina (retina) is supplied by the blood vessels of the choroid. The retina, like the brain, has a barrier so that only selected substances can get into it: the Blood-retinal barrier (analogous: Blood-brain barrier). Therefore, the pigment epithelium, which anatomically belongs to the retina, lies between the choroid and the retina. The cells of the pigment epithelium are firmly connected to each other and ensure that only required substances from the blood, which flows in the vessels of the choroid, can penetrate into the retina. The rich blood circulation in the choroid is also the cause of the undesirable "red eyes" -Effect "when taking photos. When overexposed, it shimmers through the eye in red.
Another function of the choroid is the ability of the eye to accommodate, i.e. the ability of the eye to see clearly near or distant objects. The part of the choroid that is responsible for this function is called Bruch's membrane. The Bruch's membrane contains many elastic fibers and is the opposite of the ciliary muscle, which contracts the lens for near vision and thus makes it more spherical. Distance accommodation, on the other hand, is ensured by the passive restoring force of the elastic fibers of the Bruch's membrane and thus by the choroid.
Last but not least, the choroid is also heavily pigmented and, together with the above-mentioned pigment epithelium, ensures that as little as possible of the light falling into the eye is reflected. Instead, the light is completely absorbed, which is very important for seeing in different lighting conditions. Furthermore, the strong pigmentation of the choroid prevents the uncontrolled reflection of light within the vitreous body from causing confusing stimuli on the retina.
Choroid anatomy
The choroid (Choroid) is one of the three parts of the vascular skin (Uvea) of the eye. It lies against the retina from the outside. First, the Bruch's membrane attaches itself to the cells of the retina from the outside, which receive the light impulses (Photoreceptors). The Bruch's membrane consists of connective tissue and is due to its structural proteins (Collagen fibers) and the reversibly stretchable elastic fibers too Lamina elastica called.
This is followed by a layer of small blood vessels (capillaries) that are branched like a braid. The cells of the blood vessels are spaced far apart (fenestrated capillaries) so that certain blood components can easily escape from the vessels. They are used for nutrition. These windows are sealed by the cells that receive the light impulses (pigment epithelium or photoreceptors) and the Bruch's membrane.
The last layer consists of larger vessels and is the layer with the plexus-like branched small blood vessels (Choriocapillaris) from the outside. This outermost layer of the choroid carries larger blood vessels.These are mostly veins that carry blood away from the eye. The choroid is pulled outwards by the dermis (Sclera) limited.
- Cornea - Cornea
- Dermis - Sclera
- Iris - iris
- Radiant Bodies - Corpus ciliary
- Choroid - Choroid
- Retina - retina
- Anterior chamber of the eye -
Camera anterior - Chamber angle -
Angulus irodocomealis - Posterior chamber of the eye -
Camera posterior - Eye lens - Lens
- Vitreous - Corpus vitreum
- Yellow spot - Macula lutea
- Blind spot -
Discus nervi optici - Optic nerve (2nd cranial nerve) -
Optic nerve - Main line of sight - Axis opticus
- Axis of the eyeball - Axis bulbi
- Lateral rectus eye muscle -
Lateral rectus muscle - Inner rectus eye muscle -
Medial rectus muscle
You can find an overview of all Dr-Gumpert images at: medical illustrations
physiology
The choroid contains a large number of blood vessels. These have a total of two tasks. The first important job is to nourish the outer layer of the retina. These are mainly the photoreceptors, which receive the light impulses and pass them on. The retina also consists of several layers. The more inner layers are filled with blood through a specific blood vessel, namely from the branches of the Central retinal artery, provided.
It has been observed that although the choroid has a very high blood flow due to the strong plexus formation through blood vessels, the oxygen exhaustion from the red blood cells is relatively low. This is the reference to the second important function of the choroid, namely temperature regulation. During the process of processing and forwarding the sensory cells (Photoreceptors) incoming light stimuli generate heat that is dissipated by the blood vessels. This adjusts the temperature in the eye and keeps it stable.
Choroid Diseases
Since the choroid does not contain pain fibers, pain only occurs when diseases of the choroid spread to neighboring areas supplied with pain fibers or when there is an increase in pressure. However, visual disturbances may occur, the severity of which depends on where the disease is located on the fundus of the eye. Tumors often go undetected for a long time.
Choroidal inflammation
An inflammation of the choroid (chorioditis) usually occurs as a result of an allergic reaction (immunological disease). However, it can also be triggered by foreign bodies that get into the eye from the outside or by germs from other sources of inflammation in the face and skull. The reason for this is the good blood circulation in the choroid, which not only supplies it with nutrients, but can also spread pathogens and germs into the choroid if an infection is present. Possible pathogens can be bacteria, viruses or fungi. Immune-weakened people are considered to be risk groups, as the body's own defense system cannot kill the germs sufficiently.
Since the choroid itself does not contain any nerve fibers, pain only manifests itself when adjacent structures such as the dermis or retina are affected. Tension pain occurs, usually as a result of increased intraocular pressure. In addition, as a result of the inflammation of the neighboring retina, those affected suffer from visual disturbances, cloudiness and fogging as well as a general decrease in visual performance. In most cases, a noticeably reddened eye can be seen from the outside.
The ophthalmologist will first perform an eye test to see whether there are already visual field deficits. The eye is then examined using a slit lamp in order to be able to assess the anterior and inner parts of the eye. In order to be able to see the fundus, consisting of the retina and the underlying eyes, the pupil must be spread wide. A tonoscopy is performed to determine if pressure inside the eye may have increased.
At a Chorioditis should be acted quickly, because otherwise it can lead to permanent visual disturbances or in the worst case to blindness. Immediate therapy consists of tablets containing cortisone to combat the focus of inflammation. In addition, pressure-lowering medication is given to protect the surrounding structures, such as the optic nerve head, from the increased pressure.
A choroidal inflammation can develop individually both in the course of the disease and in the degree of severity. The exact therapy should therefore be determined by an ophthalmologist.
Read more here: Choroidal inflammation
Choroidal coloboma
A Coloboma (Greek "the mutilated") is a congenital or acquired gap in the eye. In the congenital variant, the embryonic development of the eye leads to insufficient or incorrect closure of the eye cup cleft during the 4th to 15th week of pregnancy. The causes of these embryological malformations are still the subject of current research. Mutations in the so-called PAX genes, which take on many regulatory functions in embryonic development, are discussed.
Acquired choroidal colobomas are usually caused by external violence (e.g. blow to the eye, accident, etc.) or complications during operations on the eye.
Read more on the subject at: Coloboma on the eye
Choroidal hemangioma
The choroidal hemangioma is a vascular tumor (hemangioma) located in the choroid of the eye. Due to the numerous branches into many small vessels and capillaries, the tumor is also very branched and cavernous, as it follows the course of the vessels. People between the ages of 10 and 40 are particularly affected. The choroidal hemangioma is usually benign and manifests itself free of symptoms. Only when the surrounding tissue of the capillaries is affected (exudative stage) do visual disturbances such as clouded or distorted vision occur. To make a diagnosis, ultrasound or fluorescence angiography is performed to show the extent and size of the tumor. Treatment is only necessary if there is a visual threat in the exudative stage.
Choroidal atrophy
The choroidal atrophy refers to tissue atrophy due to the death of the choroid cells. This is usually the result of a degenerate tissue such as a tumor. Depending on the location, size and extent of the atrophy, this can have significant consequences for the eye.
In the initial stage, there are visual disturbances and an increased susceptibility to infections, as, among other things, the blood-retina barrier can be disturbed and germs can pass into the retina unhindered. Severe choroidal atrophy can lead to complete blindness.
Choroidal folds
Choroidal folds usually arise as a result of a mass in the eye socket, such as a tumor, calcifications or a congested pupil. This exerts increased external pressure on the eyeball. This gives way to the pressure and the individual layers of the eye, consisting of the retina, choroid and dermis, fold up. If only the choroid is affected, this does not result in any visual disturbances. However, there is a risk that small blood vessels will be pinched off by the folds and that this will lead to an insufficient supply of oxygen and nutrients. However, if the retina is also affected, the retinal folds cause visual field losses, which in the case of one-sided disease can still be compensated by the healthy eye.
Choroidal melanoma
The choroidal melanoma (Malignant uveal melanoma) is a malignant tumor that results from the pigmented cells of the choroid, the so-called Melanocytes, can develop when these begin to divide uncontrollably. It is the most common tumor of the eye, one in 100,000 in Europe suffers from it. The maximum age for the disease is between the ages of sixty and seventy. Since the degenerated melanocytes are full of the pigment melanin, most choroidal melanomas are darkly pigmented.
Like most malignant tumors, choroidal melanoma tends to spread (about 50% of cases). It is mostly spread through the bloodstream to the liver. If there is already a spread, the disease usually leads to death within a few months / years. Since the choroid, in contrast to most other parts of the body, does not contain lymph vessels, which are of great importance for the immune system, the degenerated cells often remain undetected by the body and are therefore not fought by the immune system. The symptoms of a sick person mainly include visual disturbances and double vision. Choroidal melanomas are often discovered by an ophthalmologist as an incidental finding.
Treatment options range from radiation and laser therapy to radiosurgery and removal of the affected eye.
The choroidal melanoma must be differentiated from choroidal metastases. These are rather flat, gray-brown tumors that were mostly spread from breast cancer or lung cancer. There is also the benign choroidal nevus as a differential diagnosis.
You can also read a lot more information at: Choroidal melanoma
Choroidal nevus
In contrast to choroidal melanoma, a choroidal nevus is a benign, i.e. benign, tumor. It is usually more pigmented, sharply defined and does not grow progressively. Choroidal nevi appear dark due to an accumulation of melanin (similar to a mole on the skin). It lies below the retina and does not cause any visual disturbances. Approx. 11% of the population are carriers of such a nevus, making it the most common tumor of the inside of the eye. Mostly it is innate. Because there are no symptoms, it is often noticed by chance during an eye background examination.
Rarely, in about 5 out of 10,000 cases, such a nevus can develop into a choroidal melanoma. Certain factors such as the size, location, pigmentation or accumulation of fluid in the tumor indicate an increased risk of degeneration. A choroidal nevus should therefore be checked regularly to see whether it shows a tendency to grow. A check-up should be arranged every six months. If the findings are unclear, a tissue sample (biopsy) can provide clarity. This is obtained with a small needle.
In addition to the fundus examination, fluorescein angiography, indocyanine green angiography, fundus autofluorescence and optical coherence tomography are available for examining a nevus.
Read more about this under: Birthmark in the eye
Examination of the choroid
If the doctor looks through the pupil with special devices during the eye examination (Ophthalmoscopy), the choroid can only be assessed directly with difficulty, as the retina limits the view of the choroid for anatomical reasons. The so-called ophthalmoscopic image is important for the diagnosis and course of diseases. Ultrasound examinations can also detect pathological changes in the choroid. Fluorescence angiography describes a special way of displaying blood vessels. It is an imaging procedure in which the blood flow to the fundus of the eye (see also: Fundoscopy) is observed and assessed through a medically dilated pupil by administering a suitable dye. If a choroidal tumor is suspected, a cold light source placed on the eye can cause shadowing in the area of the tumor.
