Retina of the eye

Synonyms

Medical: retina

English: retina

introduction

The retina is part of the eye and consists of several layers containing cells that absorb, transform and transmit light stimuli. She is responsible for the color and brightness vision and eventually forms the optic nerve, which forwards the impulses into the brain. For the different colors and light intensities, the retina contains different cells, which convert the light stimuli into electrochemical stimuli.

anatomy

The retina is composed of three layers. The outermost layer is adjacent to the choroid. This outer grain layer contains the sensory cells that receive the light stimuli ( photoreceptors ). The photoreceptors are distinguished by the rods, which are responsible for the night and twilight vision of the cones, which provide the day and color vision.
The cones are mainly in the center of the retina, the rods are more in the outer areas ( periphery ). The outer grain layer is followed by the inner grain layer.
This consists of bipolar cells, horizontal cells and amacrine cells. These cells receive the light pulses detected and processed by the photoreceptors and pass them on to the cells of the innermost layer. The innermost layer is adjacent to the vitreous body and consists of the ganglion cells.
The ganglion cells have long Zellausläufer and pull to a common point on the fundus (see also fundus reflection), the papilla, where they then together form the optic nerve.

The papilla itself does not contain any photoreceptors. There, therefore, no light stimuli can be perceived. Therefore, the papilla is also called a blind spot. Lateral to the temple of the blind spot lies the yellow spot, which is also called macula lutea . In the middle there is a depression. There are sensory cells, which consist only of cones. Therefore, this depression is also called the place of the sharpest vision. The retina is an evolutionary part of the intermediate brain ( diencephalon ) and has about 120 - 130 million photoreceptors.

Figure: Horizontal section through the left eyeball, seen from below
  1. Cornea - Cornea
  2. Sclera - Sclera
  3. Iris - iris
  4. Radiation body - Corpus ciliare
  5. Choroid - Choroidea
  6. Retina - Retina
  7. Front chamber of the eye -
    Camera anterior
  8. Chamber Angle -
    Angulus irodocomealis
  9. Rear Eye Chamber -
    Camera posterior
  10. Eye Lens - Lens
  11. Vitreous humor - corpus vitreum
  12. Yellow spot - macula lutea
  13. Blind spot -
    Discus nervi optici
  14. Optic nerve (2nd cranial nerve) -
    Nervus opticus
  15. Main line - Axis opticus
  16. Axis of the eyeball - Axis bulbi
  17. Lateral straight eye muscle -
    Musculus rectus lateralis
  18. Inner straight eye muscle -
    Musculus rectus medialis

Blood supply to the retina

The inner two layers of the retina are supplied by the retinal central artery ( A. centralis retinae ), which pulls the optic nerve through a common opening in the cranial bone ( foramen opticum ) from behind into the eye socket. This originates from the flow area of ​​the artery of the eye ( A. ophthalmica ), which in turn arises from the flow area of ​​the internal main artery on the neck and head ( A. carotis interna ). The outer layer of the retina is supplied via blood vessels of the choroid. The venous blood disposal takes place via the eye veins ( Vv. Ophthalmicae ).

Tasks of the retina

The retina of the eye, also called retina, takes on the task of transmitting stimuli to the brain while seeing. It is therefore responsible for what we see as an image.

The light must first pass through the cornea, the lens and the vitreous body of the eye apparatus, before it hits the retina behind it inside the eye.
The retina consists of millions of sensory cells. The reflected light information of the viewed object is picked up by the cells of the retina, sorted, bundled and finally sent via the optic nerve as an impulse to the brain. These tasks are performed by the various cell types that are interconnected in the retina.

Furthermore, the retina takes on tasks in the vitamin A metabolism and forms a kind of border between it and the directly adjacent blood vessels located in the choroid. These are used to supply the retina. Through the barrier, it ensures that no harmful substances from the blood can reach the retina. The retina is also the site of the sharpest vision, the so-called macula or fovea centralis . Here are only cones.

Physiology of the retina

If a light stimulus hits the eye, it first has to penetrate through several different structures of the eye to the photoreceptors. First, the light pulse hits the cornea in the anterior chamber of the eye, passing through the pupil, posterior chamber, lens and vitreous body.
To get to the photoreceptors, the light pulse still has to pass through the inner two layers of the retina. When the light stimulus reaches the sensory cells, this light stimulus is converted into electrochemical stimuli and transmitted to the two inner layers of the retina. The cells of the inner layer form the optic nerve, which direct the stimuli into the brain, where they are then processed and perceived.

Colors and twilight vision

For color and brightness vision, there are three types of cones, consisting of red, green and blue cones. The bars responsible for twilight vision are virtually switched off in brightness and can not perceive colors. At night, only chopsticks are active, which is why color vision is difficult at dusk and in the dark.

The photoreceptors and bipolar cells have some resting activity ( potential ). When stimulated, they pass on this information about an increase or decrease in potential. The ganglion cells in turn pass their information via electrical signals (action potentials), so they are frequency-coded. Thus, brightness and color have different frequencies whose frequency code in the brain is decoded and translated into an image.

Diseases of the retina

Retinal detachment / retina dissolves

In general, diseases of the retina are painless, since there are no pain fibers.

In a retinal detachment, the retina separates from the vessel-rich choroid. It forms a gap in which liquid accumulates. As a result, the retina can no longer be supplied by the choroid and visual disturbances occur.

Causes of retinal detachment may be inflammation, degeneration, puncture or cracking. The latter are formed by weak points or for example by bruises of the eyeball. Fluid passes through the hole and retinal detachment occurs. Since you can feel no pain in most cases, a retinal detachment can usually be determined by blurred vision. If the cracks caused by degeneration in the area of ​​a blood vessel, it can lead to small visible bleeding in the eye. If the retina has detached in the area of ​​the fovea centralis, sharp vision is no longer possible. Furthermore, there is reduced perception of light in the area of ​​the detached site. This is often perceived as a kind of veil in front of the eye. In most cases, the reason for retinal detachment is age-related cracking or pitting. The cause of this cracking is the increasing shrinkage of the so-called vitreous body in the interior of the eye during aging. Since this is connected in some places with the retina, it comes with the shrinkage to train on the retina. This results in cracks.

People who have diabetes mellitus, short-sighted or cataracted have a higher risk of retinal detachment. If the retina is torn, this can be remedied by means of a laser therapy. When the retina is detached, surgery must be performed. Unfortunately, holes in the retina or retinal detachment can not be medicated. The retinal detachments can be transformed into a rhegmatogenous detachment based on cracking, an exudative detachment in which liquid from the vessels of the choroid invades the retina and subdivides a traction retinal detachment. The latter produces scar tissue. At the site of the scarring, the tissue contracts and a train is created. Because of this, the retina may come off.

  • Symptoms of retinal detachment
  • Retinal detachment surgery

Circulatory disorder of the retina

In order to always function properly and to allow seeing as a process, the retina must be constantly supplied by the blood vessels from the adjacent choroid. In a circulatory disorder, there are failures of vision that can lead to blindness, since the retina can no longer be adequately supplied. It can affect both arteries and veins.

Basic diseases, which can lead to a closure of a vessel and thus to a circulatory disorder, are mainly diabetes mellitus, hypertension and arteriosclerosis. It is therefore important to always have the parameters of these diseases controlled.

Arterial disorders are manifested in a spontaneous, painless and direct vision loss in the affected area. If symptoms occur, an ophthalmologist should be consulted immediately within 24 hours for a chance of recovery.

Venous-related failures are not as pronounced and abrupt compared to arterial occlusions. The symptoms are usually perceived as a kind of dark shadow or curtain. A common consequence of venous circulatory disorders is a swelling in the area of ​​the sharpest vision ( macular edema ) due to which the visual acuity is greatly reduced.

  • Circulatory disorders of the eye
  • Diabetic retinopathy
  • Thrombosis in the eye

Retina torn / retinal tear

Often, the retina tears in marginal areas for no apparent reason and it creates a hole. Normally, the retina of the eye wall is located from the inside. It is held in position by a suction formed by liquid. If a tear has now formed in the retina, the suction is lost. The water from the inside of the eye gets into the space. This increasingly fills with fluid and the retina separates. The retina can completely detach within a few days.
The original cracks in the retina are usually noticeable as fast and bright flashes or as many small black dots that seem to swim in front of the affected person's eye. If the retina has detached, severe visual field defects occur.

In case of symptoms, you should consult an ophthalmologist as soon as possible. If the retina has not yet detached at this time, laser therapy is sufficient in most cases. In this case, a laser beam causes an inflammatory reaction at the affected site, as a result of which the tissue scarred at the location of the hole and thus closes it. If the retina is already lifted, laser therapy is no longer helpful and requires surgery.

Retinitis

A pure inflammation of the retina is called retinitis . Since the retina and the choroid are closely connected, the adjacent choroid is usually affected. Therefore, the inflammation of the fundus is also called chorioretinitis .

The retinal inflammation is painless. At the beginning, it also runs asymptomatic. Only in the later stage of the inflammation does it often come to those affected to a fog in front of the eyes or cloudiness in the field of vision. The extent of the symptoms depends on the location of the inflammation on the retina. The closer it is to the place of the sharpest vision, the more serious the visual limitations are.

The cause of retinal inflammation is usually bacteria, viruses or fungi that invade the retina. Furthermore, diseases such as rubella, herpes, syphilis or autoimmune diseases may be the cause of retinal inflammation. In order to fight the inflammation antibiotics are usually administered by means of eye drops. Due to its anti-inflammatory effect also cortisone is often used. In severe cases, the antibiotic must be injected by syringe.

  • Retinitis pigmentosa
  • Antibiotic eye drops

Retinal exam

After you have described your ophthalmologist the appropriate symptoms of inflammation, cracking or detachment of the retina, this will first of all perform an eye test. Thus, the ophthalmologist can assess the extent of damage to vision.

In the following, the back wall of the eye, that is, among other things, the retina and choroid, must be viewed by means of an ophthalmoscope . With this procedure, the fundus can be viewed enlarged, so that it can be determined what damage it is.

A fast treatment is always very important to avoid consequential damages. If, for example, an inflammation of the retina has already been present for a long time, it is possible that scars form on the retina which severely impair the eyesight.

As general examinations, the ocular fundus can be mirrored with the described symptoms, blood flow disturbances can be photographically visualized with the aid of fluorescein angiography, and degrees of swelling can be determined by optical coherence tomography (OCT).

  • Fundus examination
  • Intraocular pressure measurement
  • Examination of the retina

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