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.
What is the sense of sight?
We call vision, visual perception or sense of sight to one of the five senses through which humans and many animals perceive the surrounding reality. In the case of our species, vision is the most important and the most privileged of the senses, employed 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 in the objects of the environment. The radiation that is perceived is in the spectrum of so-called “visible light”, which comprises wavelengths between 380 and 780 nanometers. For that reason it is impossible to see in the absence of light.
The information offered by the view is shape, 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 more passive senses, 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 reveals huge 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.
What’s more, allow us to foresee future events from 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, the view plays a fundamental role in the composition of human society, allowing the rapid recognition of our interlocutors and also different forms of body and non-linguistic communication, or more importantly, written communication.
People lacking a sense of vision have significant difficulties to function in society, and also cannot experience visual aesthetics, that is, they cannot look at a painting, a photograph or a landscape 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, 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, they are reflected in one way or another. That reflection is captured by our eyes, by penetrating its most superficial transparent layers.
This does not happen in an uncontrolled way, but, by contracting or expanding, the iris and pupil are responsible for modulating the amount of light that enters the eye: in abundance of light, the pupil contracts, while if the light is scarce, the pupil opens 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 sensory cells (rods and cones) are, precisely, responsible for transforming light energy into nerve impulses, which travel to the brain through the optic nerve. Once there, you are nerve signals are interpreted by the geniculate body of the occipital lobe, a key process for understanding what is seen.
In fact, the images on the retina are projected inverted, 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 to the eye apparatus.
- A biochemical process, in which cells in the retina “translate” light into electrical nerve 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
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 about 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, made up 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 very 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 ducts are located, 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 depending on 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 area is blind and increases as it approaches the posterior region, where the fovea is located, a small fissure where the largest 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.
- 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 the system of transmission 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 the that 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, the cones are activated in the presence of light and allow the perception of 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 million 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 stare directly at the sun under no circumstances, nor to artificial sources of light that are comparable in intensity.
- Wear chrome or dark glasses in excessively lit environments or on days with too much sunlight.
- Don’t strain your eyes continuously, subjecting it to reading in the absence of light or exposing it only to the light of screens (cell phones, tablets, computers, etc.).
- Give your sight breaks during particularly long reading sessions, especially when in front of a screen.
- Do not introduce foreign bodies into the eye, or possibly irritating or toxic substances, and avoid touching your eyes with dirty hands.
- Go to the eye doctor or olfalmologist regularly, or upon perceiving any defect in sight.