One of the five senses, vision is responsible for seeing and its main organs are the eyes .
The eye
In humans, the eye is a sphere about 3 centimeters in diameter, where the main parts are:
- Cornea : is a transparent membrane that is attached to the sclera at the front of the eye. It allows light to enter and, together with the lens, makes it focused to the retina. Corneal transparency and curvature are essential to ensure clear vision.
- Choroid : it is the middle layer of the eye, formed by a tissue made up of blood vessels and nerves, whose functions are to maintain the temperature of the eyeball, nourish it and guide blood flow.
- Crystalline : it is a structure of elastic consistency that is thicker for the vision of what is near and thinner for the vision of what is more distant, thus allowing to adjust the focus of what is viewed according to the distance. It grows throughout the life of the human being and functions as a lens that, together with the cornea, directs the passage of light to the retina.
- Sclera : commonly called “white of the eye”, it is the outermost layer of the eye, consisting of a very dense and resistant fibrous tissue, and its function is to protect the eyeball. The muscles that control eye movements are connected to it.
- Aqueous humor : fluid that is located between the cornea and the lens, thus filling the anterior chamber of the eye.
- Vitreous humor : gelatinous fluid that is located between the lens and the retina, thus filling the posterior chamber of the eye.
- Iris : it is the colored part of the eye and is located between the cornea and the lens. It is a retractable musculature that expands and contracts, regulating the amount of light that enters the eye through an orifice called the pupil.
- Optic nerve : it is connected to the retina. It is through it that electrical impulses are transmitted to the brain, which subsequently interprets them thus generating the image that we visualize.
- Pupil : it is the dark part located in the center of the iris. Although many think it is a small circle of dark pigmentation, it is actually an orifice. Its size is increased or reduced by the iris, depending on the amount of light received. When the luminosity is low, the iris dilates the pupil so that as much light is captured as possible, and when the amount of light is large, the size of the pupil is reduced by the iris, thus decreasing the entry of light and preventing the individual is overshadowed.
- Retina : it is the innermost layer of the eye, consisting of two types of cells called rods (cells very sensitive to light that allow vision in low light conditions and detect only shades of gray) and cones (cells less sensitive to light, which distinguish colors and shades.
When looking at something or someone, this object or being reflects rays of light. This light enters the eye through the cornea and, reaching the lens, is focused clearly on the retina.
As a result of this process, an inverted image of what is focused is formed on the retina. At this point, the cones and rods send messages to the brain and this triggers electrical impulses that are transmitted to the brain by the optic nerve. The brain then interprets the received image and the vision process is complete.
Vision Diseases
- Myopia : difficulty seeing what is distant.
- Hyperopia : difficulty seeing what is nearby.
- Astigmatism : distorted vision.
- Presbyopia : known as “tired eyes”, it is a difficulty, usually caused by age, to see clearly what is nearby.
- Cataract : blurred vision
- Glaucoma : increase in intraocular pressure that can cause a decrease in visual acuity and even blindness.
- Strabismus : ocular misalignment that makes the individual unable to direct both eyes to the same point. This misalignment can be up, down, or sideways.
- Retinopathy : causes changes in the small blood vessels in the retina, which can interfere with the individual’s visual quality and can even lead to blindness.
Can Affect Vision
- Diabetes.
- High blood pressure.
- Excessive use of computers, tablets and video games.