How Do Our Eyes See?
80% of the information flow to our brain from the sense organs that allow us to perceive our environment is through our eyes.
80% of the information flow to our brain from the sense organs that allow us to perceive our environment is through our eyes. Let’s try to understand how we see with interesting information about our eyes that we may not know. Among our sense organs, it is vision that gives us the most perfect feeling. One eye is approximately 22-25 mm in diameter and weighs 7 g.
Our eyes are created in a highly protected structure inside a pyramid-shaped bone cage called the orbital cavity. Considering all the muscles in the body, the eye muscles are the most active and fastest. A blink occurs in 100 – 150 milliseconds and it is possible to blink 5 times in a second. We blink an average of 17 times a minute, 14,280 a day, and 5.2 million times a year.
Our eyes are the world’s fastest focusing lens. When looking at a distant place; When you look close, it focuses itself on seeing close in less than 1/6 of a second. It instantly adapts to the light with the rapid enlargement and contraction of the pupil, which is also a magnificent diaphragm.
Although the image is inverted on our retina, we see straight. Although we have two eyes, the image we see is one. In fact, the organ that performs the visual function is our brain, and the eyes are just the receptors that transmit the image to the brain. The optic nerve consists of nerve cell extensions in the retina, and each optic nerve contains approximately 1.2 million nerve fibers.
Six of the twelve nerve pairs that come out of our brain and control the work of our organs called head pairs are related to the eye, and the remaining six nerves control the work of other senses and organs. Also, in terms of resolution, the human eye has a resolution of 576 megapixels.
The eye basically consists of 3 layers. The outermost white-colored hard layer is called SCLERA, the vascular layer in the middle is called the UVEA, and the innermost nerve network layer is called RETINA.
Sclera; is the white part surrounding the outside of the eye and provides the integrity of the eyeball. It is also the place where the eye muscles are attached. In the center, it forms the cornea, which is called the glass layer, which is completely veinless and is the layer where the light coming into the eye is refracted the most. The cornea must always be transparent so that objects can be seen clearly. If the transparency of the cornea is impaired, enough light cannot enter the eye and vision becomes blurred. In order for the cornea to be transparent, it should not have a single blood vessel in its structure. It contains nerve cells. With this feature, the cornea and lens are places where blood does not go in the human body. The cornea receives oxygen directly from the air through the tear and provides its nourishment from both the tear and the fluid behind it.
Choroidal layer; is located under the hard layer and the vascular layer, which is the part with abundant blood vessels, takes part in the nutrition of the eye. Iris: It is the colored part that we see when we look directly at the eye. The black circle in the middle is the pupil (pupil) with a gap. The iris, which varies in color from person to person, contains muscle fibers that serve to enlarge or contract the pupil. The task of regulating the amount of light that will pass through the lens is the pupil, which is a muscular diaphragm. There are two types of muscle groups in the iris. The vertically placed muscle fibers contract, causing the pupil to dilate, while the circularly placed muscle fibers cause the pupil to contract when contracted. Thus, it ensures that the appropriate amount of light enters the eye according to the conditions. If the iris had such a function, you would only be able to see around in a certain light. A slightly dim environment becomes pitch dark, and a little brighter you would be completely dazzled. Our pupils dilate in the dark and contract in the light for better vision.
Eyepiece (lens): The transparent part with a diameter of 1 cm just behind the pupil is the lens. It is composed of protein fibers, does not contain vessels like the cornea, and has the ability to change shape. The fibers that suspend the lens from both sides govern the movement. When looking up close, the muscles contract, the middle of the lens is cambered and its refraction increases.
Retina; The third, innermost, reticulated layer of the eye is a light-sensitive layer. It is the part where the light stimuli are received. Colored and colorless images are taken by the retina and a neural impulse is generated. With these nerves, the image is given to the brain and evaluated. The image can form anywhere in the retina, but the clearest image is in the macula, called the yellow spot.
Now let’s see how the seeing thing happens. Light is necessary for a person to see. The wavelength of visible light is approximately between 397 nm and 723 nm. During vision, light beams from any object pass through the cornea and pupil, and then refract through the lens and reach the retina at the back of the eye. The eyes convert light energy in the visible spectrum into stimulation in the optic nerve. Rays hitting the retina produce potentials in light-sensitive visual cells called bacilli and cones. Each human eye contains 6 million cones and 120 million bacilli. There are no bacillus cells in the yellow spot.
The retina has a structure containing about 10 layers, and the photoreceptor cells, which are the cells that provide vision, are located in the outermost part close to the choroid layer. The pigment epithelial layer, which supports these cells, contains a large amount of melanin, a black pigment, and this absorbs light and prevents reflection from the retina. Photoreceptor cell layer is rich in vitamin A. The light reaching these cells causes an impulse to be formed in the nerve cell after a series of chemical reactions.
Impulses that start in the retina are transmitted to the visual center at the back of the brain via more than one million optic nerve fibers. The area where the optic nerve leaves the eye is called the optic disc, where there are no cones and bacilli, it is called the blind spot. In addition, after leaving the relevant vessels in the brain in the arteries and veins that feed our retina, it enters our eyes from the very central part of the visual nerve and disperses to the retina. The occipital lobes, located in both hemispheres of the brain and located at the back of your head, analyze the electrical signals and a flat image is formed. In the article you are reading, it is formed in an area of a few cubic centimeters in the vast landscape.
During vision, we actually convert the rays coming to our eyes into electrical signals and see the effect of these signals on our brain. Seeing is actually watching the electrical signals in our brain. After all, our eyes are our windows to the world, and they are magnificently created.
May the light of your eyes never go out! Stay happy, peaceful and healthy.