Vision stands out among human sensory systems due to its high complexity. The structure of the eye, the main organ of sight, is a good example of this, to the point that it has come to be used as a supposedly irrefutable argument by those who defend that life was created and designed by a god.
Analysis of the parts of the eye It can be extended to a great extent since the organs of vision are composed of many structures. In this article we will focus on the main ones and on the general description of the transduction process that causes light energy to be perceived as images.
The eyes are the basis of the visual system. These organs transform light energy into electrical impulses which, when transmitted to the visual cortex of the occipital lobe, allow three-dimensional perception of shape, movement, color and depth.
The eyeballs are spherical in shape and have a diameter of approximately 2.5 cm. They are divided into two sections: the anterior and posterior chambers, filled respectively with aqueous and vitreous humor, liquids that regulate intraocular pressure. The anterior chamber is smaller and is located between the cornea and the iris, while the posterior chamber is made up of the rest of the parts of the eye.
Unlike what happens with other sensory organs, the eye partially derived from the central nervous system Specifically, the retina, which receives light information, develops from the diencephalon, the embryonic structure that also gives rise to the cerebral hemispheres, the thalamus and the hypothalamus.
In the retina we find two types of photoreceptors, rods and cones While cones allow daytime vision and the perception of color and detail, rods are adapted for night vision and produce low-resolution black and white images.
Parts of the eye and their functions
Eyes work in a similar way to cameras.
The lens adjusts depending on the distance of the stimulus, serving as a kind of lens that allows light to be refracted; The pupil is the diaphragm through which the image enters the eye and is projected onto the retina, from where it will be sent to the brain through the optic nerve.
1. Cornea
The cornea constitutes the front part of the eye and is in contact with the outside. It is a transparent structure that covers the iris and lens and allows light refraction Tears and aqueous humor allow the cornea to function properly, since they perform functions equivalent to those of blood.
2. Iris
This structure separates the anterior and posterior chambers of the eye. The iris dilator muscle increases the size of the pupil (mydriasis) and the sphincter muscle reduces it (miosis). Iris tissue It is pigmented due to the presence of melanin ; This gives rise to the color of the eye, by which we can easily identify this structure.
3. Pupil
There is a circular hole in the center of the iris that allows regulate the amount of light that enters the eye when changing size as a result of mydriasis and miosis; This opening is the pupil, the dark part located in the center of the iris.
The crystalline lens is the “lens” that is located behind the iris and allows visual focus. Accommodation is the process by which the curvature and thickness of the lens are modified to focus on objects based on their distance When light rays pass through the lens, the image is formed on the retina.
5. Watery humor
The aqueous humor is located in the anterior chamber of the eyeball, between the cornea and the lens. Nourish these two structures and allows eye pressure to remain constant This liquid is made up of water, glucose, vitamin C, proteins and lactic acid.
6. Sclera
The sclera covers the eyeball, giving it its characteristic white color and protecting internal structures. The anterior part of the sclera is attached to the cornea, while the posterior part has an opening that allows the connection between the optic nerve and the retina.
7. Conjunctiva
This membrane covers the sclera. Contributes to the lubrication and disinfection of the eyeball since it produces tears and mucus, although the tear glands are more relevant in this sense.
8. Choroid
We call the “choroid” the layer of blood vessels and connective tissue that separates the retina and sclera. The choroid provides the retina with the nutrients and oxygen it needs to function properly, in addition to maintaining a constant temperature in the eye.
9. Vitreous humor
The posterior chamber of the eye, which is located between the lens and the retina, is filled with vitreous humor, a gelatinous liquid with a density greater than that of aqueous humor of the anterior chamber. It makes up most of the eyeball and its functions are to provide it with rigidity, cushion impacts, maintain intraocular pressure and fix the retina.
The retina is the true receiving organ of the visual system since the rods and cones, the photoreceptor cells, are located in this structure. This membrane covers the back of the eye and has a function similar to that of a screen: the lens projects the perceived images onto the retina, from where they will be transmitted to the brain through the optic nerve.
Specifically, light rays are received by the area of the retina known as the fovea which, being very rich in cones, has great visual acuity and is therefore primarily responsible for detailed vision.
11. Optic nerve
The optic nerve is the second of the twelve cranial nerves. It is a set of fibers that transmit light impulses from the retina to the brain optic chiasm From this point visual information is sent to other areas of the brain in the form of electrical signals.
