Between 70 and 90% of the world’s information is perceived through the sense of sight.. In the human species, the eyes are highly complex, fragile and delicate organs.
The eyes receive information from the outside world through light, which is transformed into nerve impulses to the brain where it is interpreted.
Next we are going to talk about what parts of this organ are so important for human beings, as well as describing the functions they perform and some diseases they may suffer.
What is the eye?
The eyes are known to be one of the most complex organs of the human body. Its main function is to detect light and send signals through the optic nerve (second cranial nerve) to reach the brain, specifically the cortex of the occipital lobe, where they will be interpreted in the form of images.
Each eye is spherical in shape, with a diameter of approximately 2.5 cm and a weight of between 7 and 8 grams. The movements of the eyes are due to the fact that they have 6 muscles inserted in the outermost part, the sclera. These muscles act in such a way that the eyes are coordinated when looking at a particular place.
The eyes are divided into two sections: the anterior chamber and the posterior chamber, with the aqueous and vitreous humors.
During embryogenesis, the eye is partially formed from the central nervous system. The retina is formed from the diencephalon, an embryonic structure that also gives rise to the cerebral hemispheres, thalamus and hypothalamus in more advanced stages of development.
The parts of the human eye
The parts that make up the eyes can be classified according to the three layers presented by these two organs:
- Outer layer: sclera and cornea
- Middle layer: choroid, iris, ciliary and crystalline body.
- Inner layer: retina, fovea, macula and aqueous and crystalline humours.
All the parts that make up the eyeballs are described below.
The sclera, also called sclera or popularly known as the whites of the eyes, is a fibrous and opaque structure whose function is to protect the internal contents of the eyeshaping it and acting like a kind of skeleton.
It is in the sclera where the muscles that allow the saccadic movements of the eyes are inserted.
The anterior part of the sclera is connected to the cornea, while the posterior part has an opening that allows connection between the retina and the optic nerve.
The cornea is a kind of spherical cap with a convex shape. which is located in the anterior part of the eye.
It is a very transparent tissue, without blood vessels but with a lot of nerve innervation, which explains why the eyes are so sensitive to external stimuli. The function of this structure is to refract and transmit light to the back of the eye.
If the shape of the cornea presents anomalies, this can affect vision, since the light introduced into the eye may be projected in different points of the retina, instead of just one. This is what produces astigmatism.
This is a layer made up of blood vessels and connective tissue. that separates the sclera and retina. This structure contains a pigment, a pigment that absorbs excess light and prevents blurred vision.
It also nourishes the retina, as well as maintaining a constant temperature in the eye.
The iris separates the anterior and posterior chambers of the eye, and forms the edge of the central hole of the eye.the pupil.
It protects the eye from the entry of too much light, functioning as if it were a camera’s diaphragm. If there is too much light, it contracts (miosis), and if there is too little, it dilates (mydriasis).
The iris has as an outstanding characteristic the power to be of several colors. When we say that a person has blue, green or brown eyes we mean this particular part of the eyes.
The color of the iris varies depending on the amount of melatonin and the pigment it possesses.
This is a dark, circular hole in the center of the iris that allows light to enter the inside of the eye.
6. Ciliary body
It’s a structure that connects the iris to the choroid.. It produces aqueous humour and is responsible for the accommodation of the eye, i.e. making the crystalline lens change shape.
The crystalline lens is known to be the natural lens of the eye.. is biconvex in shape, transparent and elastic, located behind the iris.
It does not contain blood vessels nor is it innervated, and it is supported by the ciliary body.
Because it can change shape (accommodation), it works as if it were the zoom of a camera, bulging or flattening itself to be able to focus the images that are located at different distances.
Age affects the lens. With the passage of time and, above all, from the age of 45, this structure loses transparency and increases its thickness, decreasing the capacity of accommodation.
This problem makes it increasingly difficult to read up close, resulting in presbyopia and eyestrain.
The retina is the most important inner layer of the eye.. It is a photosensitive layer in which light is transformed into nerve impulses that are sent to the brain. Contains the photoreceptors that allow vision: cones and canes.
The cones are cells that allow color vision and there are three types, each with the ability to detect the colors red, blue and green.
If there is any anomaly in the cones, one of the three primary colors of light may not be seen or may be confused by one of the other two. This problem is called color blindness.
The canes are the photoreceptors in charge of night vision. They are more sensitive to light and produce black-and-white vision.
Some vision problems may result from the beam of light introduced into the eye not being properly projected onto the retina.
In nearsightedness, light is not projected onto the retina, but in front of it, while in farsightedness, light is projected behind it.
9. Macula and fovea
The macula is located in the center of the retina, is yellow and elliptical in shape.. In its center is a small depression that is the fóvea.
This is where the highest concentration of photoreceptors is found. This part is responsible for the central vision, allowing daily actions such as reading or distinguishing people’s faces.
10. Aqueous Humor
Aqueous humor is a substance found in both the anterior and posterior chambers of the eye.. Its main function is to nourish and oxygenate the cornea and the crystalline lens, in addition to allowing the ocular pressure to remain constant.
The main components of this substance are water, vitamin C, glucose, protein and lactic acid.
If the aqueous humor does not exit the eye properly, it can lead to increased intraocular pressure, which can lead to glaucoma.
11. Vitreous Humor
Vitreous humor is a transparent, gel-like tissue found inside the eye.. It occupies about two-thirds of the eyeball and supports it.
It fills the entire eye behind the lens, crushing the retina and protecting it from impact.
Floating flies are a phenomenon that occurs in vitreous humor that can become quite annoying. These are small cells or pieces of the same mood that cast shadows on the retina, giving the sensation of having them in front of the eyes.