Retina
Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.
More about the experts All content is checked by medical journalists.The retina is the inner layer of the eyeball, a very thin and easily tearable skin. It is equipped with light-sensitive cells (photoreceptors) - rods and suppositories. The point of sharpest vision (fovea, yellow spot) and the exit point of the optic nerve can be found in its rear area. Read more about the retina: function, structure and possible health problems!
What is the retina of the eye?
The retina is a nerve tissue and the innermost of the three wall layers of the eyeball. It extends from the edge of the pupil to the exit point of the optic nerve. Their task is to perceive light: the retina registers the optical light impulses that fall into the eye and converts them into electrical signals, which are then transmitted to the brain via the optic nerve.
The structure of the retina
The retina is divided into two sections - an anterior section and a posterior section.
Anterior retinal segment
The front part of the eye retina (pars caeca retinae) covers the back of the iris and the radiating body (ciliary body). It contains no photoreceptors (photoreceptors) and is therefore insensitive to light.
The border between the rear part of the retina runs along the rear edge of the ciliary body. This transition has the shape of a jagged line and is known as the ora serrata.
Posterior retinal section
The rear part of the retina (pars optica retinae) lines the entire fundus of the eye, i.e. the inside of the rear eyeball. It has light-sensitive photoreceptors:
This part of the retina is made up of two leaves: The outer leaf (towards the outside of the eyeball) consists of a pigment epithelium (stratum pigmentosum). The inner leaf (towards the middle of the eyeball) consists of the light-sensitive layer with the photoreceptors (stratum nervosum). There is a capillary gap between the two. The two leaves are fused together in only two places - in the area of the ora serrata and in the area of the exit point of the optic nerve.
Pigment epithelium (stratum pigmentosum)
The single-layer pigment epithelium (stratum pigmentosum) lies on the inside of the middle skin of the eye and thus borders the choroid. It has elongated brown pigment granules and extends to the photoreceptors in the stratum nervosum. The main task of the epithelium is to supply the photoreceptors with oxygen and nutrients (via the blood).
Light-sensitive layer (stratum nervosum)
The stratum nervosum, the inner leaf of the eye retina, houses the first three consecutive neuron types of the visual pathway. From the outside in, these are:
- Photoreceptor cells (rods and cones)
- bipolar cells
- Ganglion cells
There are also other cell types in the stratum nervosum (horizontal cells, Müller cells, etc.).
The cell bodies of the three types of neurons (rod and cone cells, bipolar cells, ganglion cells) are arranged in layers. This results in a total of ten layers that build up the stratum nervosum of the retina.
Chopsticks and cones
The rods and cones share the tasks of light perception:
- Rods: The around 120 million rods in the eye are responsible for seeing in twilight and black and white.
- Cones: The six to seven million cones are less sensitive to light and allow you to see colors during the day.
The sensory cells border directly on the pigment epithelium and are overlaid by the other nerve cells of the inner retinal layer (bipolar cells, ganglion cells). The incident light must first penetrate these inner ones before it reaches the sensitive photoreceptors.
Cones and rods are in direct contact via synapses with neuronal switching cells that end at the optic ganglion cells. Several sensory cells end at a ganglion cell.
Yellow spot and pit of vision
The so-called "yellow spot" (Macula lutea) is a rounded region in the middle of the retina, in which the light-sensitive sensory cells are particularly dense. In the center of the "yellow spot" there is a depression - called the visual pit or central pit (fovea centralis). It only contains cones as photoreceptors. The overlying cell layers (ganglion cells, bipolar cells) are shifted to the side so that incident light rays fall directly on the cones. That is why the pit of vision is the point of sharpest vision on the retina.
With increasing distance from the fovea, the proportion of cones in the retina decreases.
Blind spot
The appendages of the ganglion cells collect at one point in the area of the back of the eye. The nerve endings leave the retina at the so-called “blind spot” (papilla nervi optici) and emerge from the eye in bundles as an optic nerve. It forwards the light signals from the retina to the visual center in the brain.
Since there are no light-sensing cells at this point in the retina, no vision is possible in this area - hence the name "blind spot".
The function of the retina
The retinal function consists in the reception of the light stimuli falling into the eye: the rods and cones register the incoming light impulses and convert them into electrical impulses. These are then transmitted via the other nerve cells in the retina to the optic nerve and on to the visual center in the brain. The visual center then processes the electrical impulses into an image.
What problems can the retina cause?
The retina of the eye can be affected by various diseases and injuries. Some examples:
- Macular degeneration: The retina is damaged in the area of the macula (yellow spot). The elderly are most commonly affected (age-related macular degeneration, AMD).
- Retinal detachment: This is where the retina detaches from the fundus. Without treatment, those affected go blind.
- Retinal artery occlusions: Rarely, blood clots enter the retinal artery or one of its side branches and block blood flow. This manifests itself as sudden unilateral blindness or visual field loss (scotoma).
- Diabetic retinopathy: Untreated or poorly controlled diabetes mellitus (diabetes) damages the smallest blood vessels in the retina. There is a lack of oxygen and the death of photoreceptor cells in the retina. Visual impairment and blindness are the possible consequences.
- Retinopathy of premature infants: In premature babies with a birth weight of less than 2500 grams, the retinal vessels are still developing. Oxygen disrupts this process, as a result of which the immature vessels close up and then proliferate.
- Retinitis pigmentosa: The term describes a group of genetic retinal diseases in which the light-sensing cells gradually die.
- Tumors: Growths around the eyes (such as retinoblastoma) can affect the retina.
- Injuries: For example, a bruised eye can tear the ora serrata - the border between the anterior and posterior sections of the retina.
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