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Video: Visual Process
The process of seeing
The part of the light that is visible to humans is in the range of 380–780 nm. In order for us to perceive these light rays and see something, a complex and composed system is necessary.
Rays of light hitting the eye are refracted several times in order to be deflected and focused on the retina. Finally, special cells are reached that are also important for the perception of light. Information reaches the brain and can be processed so that an "image" is created.
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- Visual and nerve cells
- Connection to the brain - optic nerve
The first essential areas that light reaches and penetrates
- are those of air, tear film, cornea and aqueous humor in the anterior area of the eye,
- The light is also refracted between the aqueous humor and the lens
- as well as in the transition from lens to vitreous - so that it finally reaches the fundus (retina).
Visual and nerve cells
If the light hits these specific cells (cone and rod cells), they change so that an impulse is transmitted via various nerve cells and reaches the brain via the optic nerve. The retina is peppered with millions of visual and nerve cells. While the rod cells are involved in light-dark vision and can perceive movement, cone cells “react” to certain color components of the light (eg red, blue or green light components), from which different colors are later perceived with the help of the brain.
The cone cells are diurnal - they require higher light intensity (daytime and color vision). The iris regulates the entry of light. It expands and narrows the pupil. Rod cells are involved in seeing in twilight and in the dark - and in ensuring that movements can be clearly perceived. They are distributed over the retina, but not in the center of the retina. At the outer edge of the field of view it is no longer possible to see so clearly, but movements are “recorded” well. In the center of the retina, the cone cells crowd in the so-called yellow spot (macula lutea), the point of sharpest vision. When light hits the respective cell, a nerve impulse (very low current) is generated, which is passed on to the brain via nerve cells.
Connection to the brain - optic nerve
The transition from the retina to the optic nerve takes place at the papilla. There are no photoreceptor cells at this point, so it is a kind of blind spot where no vision is possible. However, the brain makes up for this blind spot.
The optic nerve consists of many millions of nerve fibers. It represents the connection to the brain. The visual path runs through the eye socket (bones) towards the inside of the skull. Some of the nerve fibers cross at the junction of the optic nerves (optic chiasm) and continue in the opposite half of the brain. Images can therefore get from both eyes in both hemispheres to the brain areas that process them. In the midbrain there is a nerve node from which the information is relayed to the visual cortex of the occipital lobe. In this “visual center” the brain processes the information so that an image of the surroundings is created. The image impression is also linked to other impressions and linked to different regions in the brain (e.g. with the olfactory brain).The brain can also fall back on previous experiences.
- Graphics, images and details about the eye and the visual process can be found at MedUni Vienna.
- Information is also available on the website of the Austrian Ophthalmological Society.
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