Synonyms
Medical: retina
Introduction
The retina is a part of the eye and consists of several layers containing cells that absorb, convert and transmit light stimuli. It is responsible for color and brightness vision and finally forms the optic nerve, which transmits the impulses to the brain. For the different colors and light intensities, the retina contains different cells that convert the light stimuli into electrochemical stimuli.
Anatomy
The retina is composed of three layers. The outermost layer borders on the choroid. This outer granular layer contains the sensory cells that receive light stimuli (photoreceptors).
The photoreceptors are divided into rods, which are responsible for night and twilight vision, and cones, which are responsible for day and color vision. The cones are mainly located in the center of the retina, the rods are more in the outer areas (periphery). The outer granular layer is followed by the inner granular layer.
This consists of bipolar cells, horizontal cells and amacrine cells. These cells take up the light pulses detected and processed by the photoreceptors and transmit them 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 cell extensions and move to a common point at the back of the eye, the papilla, where they together form the optic nerve. The papilla itself contains no photoreceptors. Therefore, no light stimuli can be perceived there.
This is why the papilla is also called blind spot. On the side of the blind spot towards the temple lies the yellow spot, also called macula lutea. In its center there is a depression.
There are sensory cells that consist only of cones. This depression is therefore also called the point of sharpest vision. The retina is historically a part of the diencephalon and has about 120-130 million photoreceptors.
Blood supply to the retina
The two inner layers of the retina are supplied by the retinal central artery (A. centralis retinae), which, together with the optic nerve, enters the eye socket from behind through a common opening in the skull bone (Foramen opticum). This originates from the flow area of the artery of the eye (A. ophthalmica), which in turn originates from the flow area of the internal aorta at the neck and head (A. carotis interna). The outer layer of the retina is supplied by blood vessels of the choroid. The venous blood is drained via the ocular veins (Vv. ophthalmicae).
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