Sight is an organism's ability to perceive illuminated objects, mostly three-dimensional and in color. Humans see colors in the spectrum from red to violet. The eye is the organ of vision. Perceiving with this sense is called seeing.

The word "vision" is also used as a comprehensive term for a number of parameters:

  • The ability to see objects in sufficient focus. This is actual vision.
  • The ability to see objects in the periphery of the retina ("out of the corner of the eye").
  • The ability to perceive colors.
  • The ability to see depth.
  • The ability to move the eyes with the eye muscles in all directions.
  • The ability to project images onto the retina without refractive error.
  • The ability to accommodate well.
 

Function of vision

The function of vision is to be able to orient oneself in the illuminated world as objects reflect light back at different levels of brightness, in different patterns and in different colors. Information from this sense is combined with information from proprioception, the sense of touch and the organ of balance to provide a complete picture of the organism's place in the encompassing object world.

 

Functioning of the facial sense

The light-sensitive receptors of vision (the rods and cones) are located behind the retina of the eye, or eyes. The eye or eyes, in turn, are located on the front of the head in many organisms, but sometimes elsewhere, such as on the legs. With more than one eye, it is possible to see three-dimensionally.

Light enters the eye through the cornea and anterior chamber of the eye, through the pupil of the iris acting as a diaphragm and through the posterior chamber of the eye, projected by the lens of the eye and passing through the vitreous body onto the light-sensitive receptors behind the retina. There, the light impressions are transformed into action potentials in the facial nerve.

 

The visual system in the brain.

The primary system

Much of the brain has a function in processing the stimuli given off by the retina. Seeing is as much a function of the nervous system as it is of the eyes.[1]

  • Retina. In the retina, (analog) visual stimuli are converted into (digital) action potentials, electrical stimuli in the receptor (sense organ) cell. This conversion takes place through a chemical reaction in the cell(the rods and cones). This action potential is transmitted to ganglion cells.
  • The offshoots of these cells form the optic nerve, the facial nerve. This leaves the eye through the blind spot.
  • The two facial nerves meet in the chiasma opticum, where the fibers coming from the retina located on the side of the nose cross. In the brain, therefore, the image that both eyes receive from the right or left is combined, making three-dimensional (depth) vision possible. From there the nerve fibers continue as tractus opticus
  • In the corpus geniculatum laterale, a part of the brain nucleus the thalamus, the action potential is transmitted to the next neuron. Here the information is further organized, for example, the images of both eyes are combined.
  • From here the nerve cells fan out widely as radiatio optica and reach the primary visual cerebral cortex, located at the very back of the skull (occipital), where one becomes aware of the stimulus; also called area 17 or area striata.
  • Other nerve cells switch in the area of the colliculi superiores, part of the brain stem, to nerve cells that regulate eye muscles and pupil dilation (oculimotor nerve) via the oculimotor nerve, trochlear nerve and abducens nerve.
  • Yet other cell offshoots from this area run to the spinal cord. These cells enable fast reflexes; even before you consciously see what is going on, your body has already reacted. The time it takes for a stimulus from the retina to reach the cortex is 0.1 seconds.
  • Surrounding it is the associated visual cerebral cortex, area 18, which allows recognition of patterns. Area 19 receives impulses from area 18 and from the corpus geniculatum laterale, partly through the thalamus. From there, connections are made to memory, face recognition and so on.

Dorsal and ventral system

Source: liv.ac.uk[2].

  • Through the dorsal system, stimuli go to the top of the brain (the parietal portions), the frontal portions (the frontal cerebral cortex) and to the primary motor cortex (gyrus praecentralis/sulcus centralis) which controls the muscles. The frontal cortex makes the decision what to look at, the parietal cortex is needed to consciously focus your gaze on something.
  • Through the ventral system, the stimulus reaches the temporal lobes, the temporal lobes of the brain. Here there is a database of shapes, figures, familiar faces and so on.

 

Cerebral blindness, CVI

In addition to eye disease or eye damage, a person can be partially sighted or blind due to damage to the nervous system. This can range from half-sided blindness, for example, not seeing what is approaching from the right, to CVI, in which the patient cannot process what his eyes are telling him and the patient does not focus the gaze.

 

Types of perceived light stimuli

There are two types of light stimuli: light with color tones and light with gray tones. In both cases, photons are converted into action potentials by specialized receptors.

Light stimuli with color tones activate the light-sensitive receptors specialized in colors, the cones, located mainly in the center of the retina, on the yellow spot. There are three types of cones: Cones that are sensitive to roughly blue, green and red light. In the brain, these primary colors are mixed into the perceived true color. The cones work only when there is sufficient light.

Light stimuli with gray tones activate the light-sensitive receptors specialized in shades of gray, the rods, which are mainly located next to the center of the retina. The rods are useful in dim conditions for the organism to still orient itself.

 

Treatment BeterKlinic

BeterKliniek is the clinic for Integrative Medicine that bridges regular and non-regular medicine.

An van Veen (physician) and Michael van Gils (therapist) look for the cause of a condition or disease. That is where the treatment starts otherwise, as people often say, it is 'carrying water to the sea'. We call this cause medicine. Sometimes it is also desirable to treat the symptoms (at the same time). We call this symptom medicine.

Chronic disorders often have their cause in epi- genetics. You can schedule a free informative telephone consultation (phone number 040-7117337 until 1 p.m.) at BeterKliniek to discuss your symptoms so that we can provide you with further advice.