• What is the sense of sight?
• What is the sense of sight for?
• How does the sense of sight work?
• Eye anatomy
• Why do we see in colors?
• Eye care

We explain what the sense of sight is, what it is for and how it works. Also, the anatomy of the eye and why we see colors.

For the human being, sight is the most important sense.

What is the sense of sight?

We call view, visual perception or sense of sight to one of the five senses through which the human being and many animals perceive the reality surrounding. In the case of our species, vision is the most important and the most privileged of the senses, used not only in observing the environment and our interlocutors, but also in the act of literacy, fundamental in human societies.

Visual perception can be defined as the ability to extract information from the effects of electromagnetic radiation on objects in the environment. The radiation that is perceived is in the spectrum of the so-called “visible light", Which comprises wavelengths from 380 to 780 nanometers. For that reason it is impossible to see in the absence of light.

The information offered by the view is in the form, color, position, movement, texture. On the other hand, vision is an active sense, which can be directed and suppressed at will (just close the eyelids), unlike other senses of a more passive nature, such as smell or hearing, which mainly depends on the functioning of the eyes. eyes, but in which different components and internal physiological processes also intervene.

It is a complex process, in which different environmental, physical and mental factors intervene to produce a more or less objective perception of objects.

What is the sense of sight for?

Vision is a very powerful sense, insofar as it reveals enormous amounts of information about the environment. The dimensions of things and spaces (width, height and depth), colors, movement, texture and other similar experiences of the real are possible thanks to it.

In addition, they allow us to foresee future events based on their distant perception: a human being on the horizon line can perceive objects up to 5 kilometers away, if the weather conditions are favorable.

On the other hand, sight plays a fundamental role in the composition of the society human, allowing the rapid recognition of our interlocutors and also different forms of communication corporal and non-linguistic, or more importantly, the written communication.

People lacking a sense of vision have significant difficulties to function in society, and also cannot experience the esthetic visual, that is, they cannot look at a painting, a Photography or a scenery and delight in its poetic or symbolic content. To some extent, the entire human civilization is built on the visual perception of the universe.

How does the sense of sight work?

For visual perception to occur, there must be visible light around it, that is, electromagnetic waves of sufficient amplitude to be captured by the human eye. These waves impact the surface of objects and, depending on their nature, are reflected in one way or another. This reflection is captured by our eyes, when penetrating its most superficial transparent layers.

This does not happen in an uncontrolled way, but, when contracting or expanding, the iris and the pupil are in charge of modulating the amount of light that enters the eye: in abundance of light, the pupil contracts, while if the light is scarce , the pupil is opened to let in as much of it as possible. Once this is done, the lens focuses on the perceived object, to project its image against the backdrop of the retina.

The retina operates as a screen, whose cells Sensory (rods and cones) are precisely responsible for transforming light energy into nerve impulses, which travel to the brain through the optic nerve. Once there, these nerve signals are interpreted by the geniculate body of the occipital lobe, a key process for understanding what is seen.

In fact, images they are projected inverted on the retina, as occurs with the so-called "dark cameras" (the principle behind the photography technique), and it is the brain in charge of "straightening them".

Thus, the process of visual perception comprises three different processes:

• A physical or optical process of entry of light waves into the eye apparatus.
• A biochemical process, in which cells in the retina "translate" light into nerve electrical information.
• A neurological process, in which the brain recognizes and interprets what is perceived in light of the immense amount of information it already has stored.

Eye anatomy

Sight is possible thanks to the interaction of the various components of the eye.

The eye is a complex organ, which encompasses much more than what we perceive with the naked eye, and which can broadly be divided into three distinct segments: the eyeball, the optic pathways and the attachments of the visual apparatus.

The eyeball. It is the eye itself, that is, a hemispherical structure of around 24 mm in diameter, which is housed in a pair within the orbital cavity of the skull. It is what we perceive when we see another in the eyes. However, the eyeball is structured in three layers and three different chambers, which are:

• The outer or sclerocorneal layer. The outermost region of the eye is a layer that covers and protects it, and which in turn includes: the sclera, the "white" part of the eye, composed of fibrous material and covered with a protective mucosa called the conjunctiva; and the cornea, the eye's optical "window," a transparent portion of the outer membrane that is poorly vascularized (does not bleed) but has many nerve endings.
• The intermediate or uvea layer. Located under the outer layer, it is the vascular layer of the eye, where most of the blood conduits are, and which in turn includes: the choroid, the posterior region of the eye, which apart from nourishing with oxygenated blood, prevents escape of light to undue regions; the ciliary body, where the fluids that fill the eye are secreted and the ciliary muscle that allows the lens to focus the gaze is also controlled; and finally the iris, the colored portion of the eye, capable of expanding or contracting depending on the absence or presence of light. Between it and the inner layer is the crystalline lens, the natural lens that allows to focus the view, accommodating itself according to the distance or proximity of objects.
• The inner layer or retina. This is the region of the eye that is sensitive to light and where the images we see are formed. Its anterior zone is blind and increases as it approaches the posterior region, where the fovea is located, a small fissure where the greatest number of visual cells are concentrated (rods and cones, named for their shape, and responsible for vision central and peripheral respectively) and the point of maximum concentration of sight occurs. In addition, it has a blind area called the papilla, where it connects to the optic nerve.
• The anterior chamber. It is the region of the eyeball between the cornea and the iris, filled by aqueous humor, a transparent liquid produced by the ciliary body in order to preserve internal pressure and the shape of the eyeball.
• The rear chamber. Located between the iris and the lens, it is where the ciliary processes occur.
• The vitreous chamber. The largest cavity of the eye, located between the lens and the retina, is filled with a transparent gel called the vitreous humor. The latter fixes the retina in place and keeps the structure of the eye intact, in addition to preserving its shape against blows or sudden movements.

Optical pathways. It is about the transmission system of nerve impulses from the retina to the brain, through the optic nerve.

The annexes of the eye. They are the set of muscles, cavities, glands and mucous membranes that surround, support and protect the eyeball. They include the ocular cavity, the eyelids, the lacrimal glands and the tear ducts, as well as the six different muscles of the oculomotor system: the superior oblique muscle, the superior rectum, the medial rectum, the lateral rectus, the rectum. inferior and inferior oblique. The levator muscle of the upper eyelid is added to them, since the lower one is immobile.

Why do we see in colors?

What we commonly call "color" is a certain wavelength that objects reflect, that is, the surface of things absorbs most of the electromagnetic spectrum while reflecting another portion, and the latter is what we can perceive with our eyes.

Similarly, an object that does not absorb any ray of light, but reflects everything, will be white; Conversely, one that absorbs the entire spectrum and does not reflect anything will be black. If the light rays do not even hit the object, but pass through it, it will be invisible or transparent.

As for the human eye, it is important to know that our photosensitive cells are capable of perceiving different modes of light: the rods are activated in the dark, for example, and allow us to capture the contrasts: white, black and intermediate gray.

Instead, cones are activated in the presence of light and allow us to perceive colors: a certain type of cone is sensitive to red light, another to blue and another to green, and by combining these three primary colors, our brain recomposes more than 20 millions of different colors.

Eye care

Vision care focuses on the protection and conservation of the eyes, and for this it is important to follow the following indications:

• Do not look directly or fixedly at the sun under any circumstances, or at artificial sources of light that are comparable in intensity.
• Wear chrome or dark lenses in excessively lit environments or on days with too much sunlight.
• Do not force your eyes continuously, subjecting it to reading in the absence of light or exposing it only to the light of the screens (cell phones, tablets, computers, etc.).
• Give your eyes breaks during particularly long reading sessions, especially if they are in front of a screen.
• Do not introduce foreign bodies into the eye, or possibly irritating or toxic substances, and avoid touching the eyes with dirty hands.
• Go to the ophthalmologist or olfalmologist regularly, or when perceiving any defect in sight.