Eyes convert traveling electromagnetic waves (light) into electro-chemical signals which the brain then processes into an image.
Although light is a wave, we will focus on geometric (ray) optics for this explanation, and not concern ourselves with wave-optical effects such as diffraction and interference..
First, light passes through the cornea (the clear front layer of the eye).
The cornea is shaped like a dome and bends light to help the eye focus.
Some of this light enters the eye through an opening called the pupil (PYOO-pul).
The iris (the colored part of the eye) controls how much light the pupil lets in..
The mechanism by which the light stimulus is transduced to nervous excitation is described.
The absorption of a photon by the visual pigment-rhodopsin, a chromoprotein-causes a photo-chemical reaction, which is followed by a cascade of dark reactions of rhodopsin..
Light enters through the lens then when the lens functions with the cornea to focus light aptly on the retina.
When light passes the retina, special cells referred to as photoreceptors convert light into electrical signals.
These signals pass from the retina to the brain through the optic nerve..
The eye focuses on objects at varying distances by accommodation, or the use of muscles to change the curvature, and thus the focal length, of the crystalline lens.
In its most relaxed state, the crystalline lens has a long focal length, and the eye can focus the image of a distant object on the retina..
The human vision system takes information from the world in the form of light that strikes the eye's retina after reflecting off of objects.
Somehow the system takes the two-dimensional information from the retina and recreates a three-dimensional world in experience..
The sense of vision involves the eye and the series of lenses of which it is composed, the retina, the optic nerve, optic chiasm, the optic tract, the lateral geniculate nuclei in the thalamus and the geniculocalcarine tract that projects to the occipital cortex..
The “Vision Center,” is located in the back part of your brain (the occipital cortex or lobe).
It is responsible for decoding the electrical information coming from the retina.
The vision center interprets the electric form of the image, allowing you to form a visual map..
Vision Science is the source of an array of research questions relating to how we see, how and why vision fails, and what can be done about it..
A geomagnetic field in the order of less than 50 μT reduces visual discrimination threshold and increases the photopic sensitivity of the visual system by 6–7% [ 41 ].
Besides the widely known image forming function, the visual system plays a crucial role in the perception and maintenance of circadian rhythms (Box 3.5 ).
Vision cannot be discussed without knowing the physical properties of optics.
The eye receives light that then is traduced into energy.
That energy goes into the optic nerve as an action potential and travels to specific nuclei in the brain, where it is processed.
One of the special non-image forming functions of the visual system is the perception of magnetic field (Box 3.3).
Geomagnetic field passes freely through mountains, oceans, and air, and many taxonomic classes of creatures are capable of detecting it [31,32,33,34,35,36].
A wide variety of animals including mammals, fish, reptiles, insects, and bird.
Besides the widely known image forming function, the visual system plays a crucial role in the perception and maintenance of circadian rhythms (Box 3.5).
Circadian rhythms are fluctuations of different events based on an approximately 24-h period [42].
Retina autonomously functions as an intrinsic timekeeper [43, 44].
The retina is the masterpiece .
Perception of the motion by the visual system not only comprises the movement of the object but also reduces the effect of head and eyes movement of the individual .
One of the special non-image forming functions of the visual system is the perception of magnetic field (Box 3.3 ).
The function of the visual system is far beyond simply focusing the light beams to produce an image.
To picture the adaptations to reduce the artifact and enhance the quality of the image, in the first section, we follow the light beams, as they are incident on the surface of the cornea to focus on the retina.
