Retina
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The retina (Latin Retina) is the photo-sensitive layerat the rear inside of the eye of vertebrate animals and unite Tintenfischen. Into their the hitting light, after it crossed the cornea/callosity, the lens and the glass body, is converted into nerve impulses.
anatomy of the retina of humans
layer
the retina rests upon on the vein skin (Choroidea), which supplies the retina with nutrients. The retina becomesfrom the glass body (corpus vitreum) inward limits, which besides by its being final jerk for the contact between vein and retina provides. Direct and firmly connected with the middle eye skin the retina is only in a circular region in the iris rangeand at the entrance of the Sehnerven (Papille). Therefore a retinal detachment is usually only briefly locally limited and can spread untreatedly over large ranges of the field of view.
cells of the retina
the retina is of defined layers composed,which from specific cell types or subzellulären Kompartimenten of these cells exist. A special meaning is attached here to the photo receptor cells . The photo receptor cells are highly polar cells, which from an external segment, an interior segment, the Zellkörper and an axon with a specialized synapse toEnd exist. In principle one differentiates types with respect to the retina between two photo receptor cell -: Stäbchen and tap („rods “and „cones “). The Stäbchen are in seeing with weak lighting (skotopisches seeing), the taps are specialized for the color seeing (photopisches seeing) responsible.
Humans are tri chromates, it exist thus to three kinds of tap with different absorption maxima. Simplified one can say that there are red-sensitive , green-sensitive and blue-sensitive taps. The nervous system combines the attraction of the three kinds of tap, around the incidentTo assign light a color. The taps are less lichtsensitiv than the Stäbchen. Therefore the color feeling changes at night, the Purkinje effect in such a way specified. Therefore the proverb comes: At night all cats are grey (to noticing: with S täbchen seesone s chwarz/white, with the Zap f EN F arben).
Already only one light photon can activate a Stäbchen. However several Stäbchen must be activated, so that the retina signals the presence of light. With the impact of a photon inDiaphragm pile of the photo receptors stored Rhodopsin experiences the latter a Konformationsänderung. Thus an enzyme cascade is released, the so-called visual signal transduction cascade, which finally leads to the change of activity of the nerve cell (tap such as Stäbchen). For the clearing-up of the meaning of the Retinals the American received 1933-1958Biochemist George forest 1967 the Nobelpreis for medicine.
Photo receptor cells lie in a distance from 6µm of in vein far away, that are comparable with the distance of the diodes in a CCD of 10µm.
The photo receptors become among themselves by two different types of horizontal cellsinterconnected. They serve thereby and. A. to the contrast reinforcement of the optical perception by lateral inhibition of neighbouring photo receptors.
The moreover one the bipolar cells become by the photo receptors internal fourth. In the Säugetierretina gives it depending upon kind eight to eleven tap-steered bipolar cells and oneType of Stäbchen steered bipolar cells.
From the bipolar cells again the Amakrinzellen becomes internal fourth. Amakrinzellen provide - similarly as before the horizontal cells - for one both lateral and vertical interconnecting of the neural network in this layer of the retina and carrylikewise to the modulation of signal processing. Altogether it gives over 30 different Amakrinzelltypen.
Those the bipolar and Amakrinzellen cells downstream are the ganglia: this Neurone passes the light attraction on now over the optical nerve (Nervus opticus) to the brain. Altogether leaveup to 20 ganglion cell types differ. Among them is a third group of light cells; this contains the pigment Melanopsin. Such cells were discovered compared with the remaining types only recently and are therefore still to a large extent unexplored.It was already proven that the Melanopsin cells work an important role as photo receptors and played with the function of the “internal clock”. They send signals to the SCN (Suprachiasmati nucleus), in about DIANE rhythms generated and so to time information to the bodypassed on become (see Chronobiologie)
layers of the retina
the light the entire retina penetrates and by the photo receptor cells is only detected. From the glass body to the vein skin one can differentiate the following laminated structure with the healthy retina.
Epiretinale or internal border diaphragm (ERM/ILM epiretinal/internal limiting diaphragm)
the internal boundary layer of the Retina is possibly the basal and plasma membrane of the Müller' cells, as well as different glial cells. It consists beyond that of Kollagenfasern and Proteoglykosiden.
Thoseinternal border diaphragm (Membrana limit to externa) this in the optical microscope homogeneous appear-ends layer forms the internal delimitation against the glass body. It covers the entire Retina and changes in front with somewhat rough ores a structure into the Zonulalamelle.
The older Histologen was thatOpinion that the brush-like final feet of the Müller supporting fibers are firmly embodied in the border diaphragm, the latters thus as gliöses product to rate is. The electron microscope could show however that the internal border diaphragm has the character of a modified basal diaphragm and of thatToes of the Müller cells to be clearly defined can. The clinically provable strong adherence of the diaphragm to the Retina probably comes off by the intermediate layer filled with cement substance, which connects the Gliafortsätze of the Müller cells with the border diaphragm.
GARDNER seizes thoseBorder diaphragm as peripheral compression of the glass body fabric up, since their fiber lamellas schichtweise stand out against the Retina and change into the glass body diaphragm. Thickness of the border diaphragm amounts to approx. 2- 3 µm.
nerve fiber layer (NFL - nerve fiber more layer)
existsfrom accumulations of the nerve fibers of the deriving nerve cells. They carry the information of all photo receptors outward. In the Sehfleck (Makula) the density is smallest and the fibers stretches star shaped outgoing of the Makula an elbow up to the blind mark (at thatthe Sehnerv the eye leaves). A destruction of this layer entails a first partial, irreparable going blind (greener star). In this height are also the internal blood vessels of the Retina (up to the container-free range in the proximitythe Makula).
This unites those about 1 million new rites of the ganglion cell layer, which pull to the Papille. These nerve fibers are Markless and receive their Mark sheaths only after the withdrawal from the Bulbus. On the way to the Papille the Sehnervenfasern shows a characteristicProcess, as only the fibers from the Fovearegion select the direct way, around so the so-called. to form „makulo papilläre bundles “. All of far peripheral coming fibers run around this bundle arc-shaped. Here they never cross a meant boundary line (Rhaphe).
The more peripheral nerve fibers lie most deeply in the fiber layer, if they pull to the Papille and take therefore one more peripheral position in the Sehnerv. More near convenient fibers lie more superficially, thus come them in the Sehnerv also more central to lie.
Also centrifugal fibers - from the brain to the Retina - were described, its function and meaning are however uncertain occasionally. Some authors assign restraining functions in the Sehakt to them, others bring them in connection with the container innervation of the retinalen container net.
Exceptthe Sehnervenfasern are in this layer still Neuroglia, straggler ganglion cells and the larger containers of the retinalen container system present. Thickens this layer: approx. 20- 30 µm.
ganglion cell layer (GCL - ganglion cell more layer)
Zellkörper with cores of the nerve fiber layer.The dendrites of the ganglion cells light up into the adjacent IPL and take up the signals of the bipolar cells and the amakrinen cells. The impulse is passed on over the axons of the ganglion cells, which run in the nerve fiber layer and itself to the Nervus opticus bundle.
The ganglion cell layer builds itself from the Zellkörpern of the 3. Neuron up. The cell size is very differently, the situation of the cells in the peripheral Retina einschichtig, in middle and central zones multilevel. Beside the ganglion cells are still Neuroglia and branchesto find the retinalen containers. Thickness of the layer: approx. 10 to 20 µm
inside plexiforme layer (IPL - internal plexiform more layer)
last preprocessing stage before the signal to the brain one passes on. Axons of cells of the INL meet hereon the dendrites of the ganglion cells.
The internal fiber layer (internal plexiforme layer) this layer exhibits the new rites of the bipolar cells and the dendrites ganglion and amakrinen cells. Beside these elements occasionally horizontal cells and cells of the Neuroglia also deplazierte are found. Thickens this layer 20 to 30 µm.
internal core layer (INL - internal nuclear more layer)
Zellkörper and also cores of functionally strongly different cells are here in varying height arranged. Above all bipolar cells, in addition, Amakrinand horizontal cells, as well as the Zellkörper of the neural supporting fabric, the Müller' glial cells, are here settled.
The internal grain layer (internal granular layer) This is the variation-richest cell layer of the Retina, because are in their four different cell kinds:
Furthest outside liethe horizontal cells, then follow the Zellkörper of the bipolar cells and Müller supporting fibers, at the internal delimitation lie the Amakrinen cells. Entirely one can speak from 10 to 12 cell layers. Thickness of the internal grain layer 30 µm.
exterior plexiforme layer(OPL - more outer plexiform more layer)
dendrites of the bipolar and horizontal cells are interconnected with the synaptic ends of the photo receptors and to form thus the first stage of the intraretinalen data processing.
The outside fiber layer (plexiforme o express. retikuläre layer) this layer places thoseConnection between receptors and the bipolar cells ago. It contains the extensions of both cell kinds, besides still extensions of the horizontal cells and the Müller supporting fibers. In the middle section the synapses the switching places from first are appropriate for this layer to the second neuron. Thickens this layerapprox. 20 µm.
In the Übergangszone to the next layer lies the deeper supply network of the retinalen capillaries, which are descendants of the central Netzhautarterie. These containers run very constantly in one level and hardly advance into other layers.
Expresses core layer (ONL - outer nuclear more layer)
layer of the Zellkörper and cores of the Photorezeptoren. Stäbchen and taps are grouped parallel next to each other and extend their thickened lichtsensitiven extensions, the external segments, toward the RPE.
The outside grain layer (granular expressesLayer) this is formed by the receptor cell bodies with core. The cores of the taps lie in an individual layer close of the border diaphragm, those of the Stäbchen form 4 to 6 layers. An exception of this arrangement exists in the Fovearegion, where thosealso taps are multilevel stored. Particularly to note it is that in this layer substantially more core are to be found, as in the layer of the bipolar and ganglion cells. Thickens this layer amounts to approx. 40µm.
external border diaphragm (ELM -eXternal limiting diaphragm)
is formed by Ausläufer of the Müller cells and celladhesion - connections (Adhering junction) with the photo receptor cells.
The outside border diaphragm (Membrana limit to externa) the appearing light-microscope homogeneous boundary layer between outside and internal section of the receptors, provedelectron microscopicly as a layer of horizontal running extensions of the Müller supporting fibers.
This fibrilläre network leaves punctiform openings for depresses the receptors freely. In the region of the Ora serrata the outside border diaphragm in the substance continues, those the twoLayers of the ciliary epithelium connects.
internal segment (IS - internal segment)
the interior segment is the range of the photo receptor cells, which contains Mitochondrien and endoplasmatisches Retikulum (IT). Here among other things the protein biosynthesis and other metabolic activity take place. Are separatedthe inside of the outside segments by a narrow connecting cilium, by which all materials for the external segment must be transported actively.
here the external segments of the Photorezeptoren of the connecting cilium
extend exterior segment (OS - outer segments)up to the RPE. At the connecting cilium new disk diaphragms, diaphragm cutting off develop bepackt with Rhodopsin. Rhodopsin is stored into the disks and initiates the visual signal transduction. By the new synthesis these disks induce themselves to the RPE and are phagocytiert there.
Retinales pigment epithelium (RPE - retinal pigment epithelium)
whole outside is limited the retina of the retinalen pigment epithelium (RPE), which forms the interface between the retina and the vein skin (Choroidea for a hexagonally developed, einschichtigen epithelium,). The cells of theRPE contain colored Melanosomen, which functionally light filter represents by Melanin black. Basally these cells show deep furrows, which serve the better exchange of material with the blood vessels of the Choroidea. Apically finger-like, mikrovilläre extensions of the RPE embrace the photo receptor cells. RPE cells their occurringfrom blood the strongly vaskularisierten Choriocapillaris (the strongly supplied with blood boundary layer of the vein skin). They represent also functionally a light filter (under Melanineinlagerungen) and serve the nutrition of the Photorezeptoren, to the Recyclen of the old disk diaphragms of the photo receptor external segments as well as the regeneration of thebleached Retinals from activated Rhodopsin.
The pigment epithelium due to the embryo-logical development is usually called the pigment epithelium outermost layer of the Retina, although it stands with the actual Sehvorgang only indirectly in connection. This in as much as it for thoseRegeneration of the Sehpurpurs and for the metabolic procedures in the receptors of of great importance is. If one tries to separate the individual layers of the Bulbuswand with dissecting an eye, then usually the pigment epithelium remains sticking to the underlying vein skin, althoughit from the same Keimblatt as the Retina develops, for the Ektoderm, while the vein skin from the Mesoderm forms.
special regions of the retina
the place of sharpest seeing
the place sharpest seeing are the yellow Fleck*, also Makula or Sehgrube. Their center is the Fovea, also Fovea centralis mentioned, because it lies exactly, where a ray of light perpendicularly incident by the pupil hits. The Fovea has a diameter ofapprox. 3mm. Only with the Makula largest visual acuity, as one needs it for instance during the reading, is reached. The surrounding retina essentially serves the surrounding field perception, recognizing things “from the eye angles”. In the case of heavy damage of the Makula, e.g.by the ageconditioned Makuladegeneration (AMD), one does not know any more vintages or driving a car. The Makula corresponds also to the range, within which the eye can notice an equally sharp illustration during central focusing (approx. 1°). In addition the eye curvature is with the normalsichtigen eyetoo strongly and the picture is peripheral blurred noticed.
- by Soemmering 1779 imported name should be avoided it there is missverstänlich. Besides the ranges do not agree with view with the ophthalmoscope and with the corpse eye in their expansion.
The blind mark
blind mark is called the place of the retina, at which the Sehnerv (Nervus opticus) withdraws from the eye. Since the sensory nerves, which derive the information, on which for inside, thus in the path of rays are appropriate, is onthe depressing place no place for a continuous receptor layer. Here are therefore no light receptors, the mark are thus really blind. The fact that we do not have a blind mark in our visual perception “in the picture” is because of the auxiliary effect. Thatvisual system uses information, which supplies the receptors in the environment of the blind mark, in order to supplement the visual picture.
illnesses of the retina
the most important illnesses of the retina are:
- Diabeti Retinopathie as subsequent condition (badly adjusted) of a sugar illness
- Makuladegeneration
- retinal detachment
- of container catches (Ischämie, Infarkt)
- Retinitis pigmentosa
- Retinopathia centralis serosa (retina removal) Retinopathia
- swell-caused pigmentosa (innate hereditary disease of the retina)
- hypertensive Retinopathie (by blood high pressure retina illness caused)
- eklamptische Retinopathie (with pregnant women in the context of Eklampsie arising retina illness)
- Retinopathia praematurorum (retina illnesswith earlyborn)
- Azoor of acutes zonale okkulte outside Retinopathie
investigation procedure (diagnostic procedure)
Apart from the standard method of the lighting of the eye background with a gap light lamp and the view of the reflected light with a Funduskamera,in the last years several different procedures for the retina diagnosis were established.
The most outstanding method is the optical Kohärenztomografie (OCT), which extends the illustration by the third dimension. This makes possible the preparation of highly soluble sectional views or also 3D- Tomogrammen with a quality comparable to the histological picture.
here can be dissolved the individual layers and measured in their thickness. Thus finest differences can be determined,for the custom-made therapy in the further treatment process, or also when testing medicines are relevant.
Further investigation and evaluation possibilities existon electricalphysiological level by
- the Elektroretinogramm (suppl.)
- the Elektrookulogramm (EOG)
as well as on the level of the retinalen blood circulation by
- those To fluorescence angiography (also FLA, FAG or Angio shortened)
- the Indozyaningrünangiographie
see also
vein skin, Uvea, break diaphragm, Emmert law, visual signal transduction
Web on the left of
- miniature picture overview retina of mammals
- The Organization OF the Retina and VisualYou
- consider system Dendritic processing into
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