All About Human Eye
Eyes are a part of our body that we used to see everything. Do you know how do eyes work so that we can see? To answer the question, we need to learn the parts of the eye first so we can know each function in seeing process.
The Part Of Human Eye
From the figure below, you can see the complete part of the human eye and their position.
Cornea
Cornea functions in receiving and transmitting the light and also to protect the eye lens from feathers.
Iris
Iris is a membrane in front of the eye lens that forms a circular chink. Iris functions in giving a color of the eye and arranging the intensity of the light entering the eye. There are so many colors of the eye. This color is caused by melanin that contains in the iris.
Pupil
The pupil is the circular chick formed by iris. The wide of the pupil is controlled by iris based on the intensity of the light entering the eye. At dark or dim condition (less light intensity), the iris relaxes so that the pupil enlarged. As a result, more light enters the eye.
At bright condition (high light intensity), the iris contracted so that the pupil becomes smaller. As a result, the light entered to the eye decreases.
Eye Lens
The eye lens is made of transparent material, fibered, and elastic and also convex in shape. The eye lens functions in constructing the image of an object. The image formed by the eye lens similar to the image formed by a convex lens – real, upside down and smaller in properties.
Retina
The retina is the back part surface of the eye. It functions as a screen to catch the image formed by eye lens. The retina consists of yellow grains, which are very responsive to the light.
Eye Nerve
The eye nerve functions in continuing the signals received by the retina to the brain. The brain process and translates the signals so that we can see the object in upright.
From the part of the eye above, now you can know each simple functions of it in seeing process.
The Accommodation Power of Eye
An object (near or far) can be seen clearly because its image formed by the eye lens falls exactly at the retina. Why does the image of an object fall exactly at retina although its distance is change?
The answer is because the eye lens is elastic (it can change to thin of thick shape). Because eye lens can change the shape, its focal length can change according to the need, therefore the image of an object can be arranged to fall exactly at the retina.
The ability of the eye lens, to thicken and to thin in order to produce an image exactly at the retina is called the accommodation power of the eye.
When the eye accommodates maximally, the eye lens thickens. As a result, the focal length of the eye increases. On the other hand, when the eye accommodates minimally, the eye lens becomes thin so that the focal length of the eye decreases.
Because of the accommodation power of the eye, the eye has near point (punctum proximum) and a far point (punctum remotum). A near point is the nearest point of an object to the eye that still can be seen clearly by the eye, which the eye accommodation maximally.
A far point is the furthest point of the object to the eye that still can be seen clearly by the eye, in which the eye does not accommodate. So the eye can see an object clearly if the object is placed between the near point and the far point.
Eye Aberration
A normal eye has a near point at a distance of 25 cm and a far point at a distance of unlimited. If the accommodation power of the eye lens decreases, then it has suffered an eye aberration.
Nearsighted Eye (Myopia)
People who suffer nearsighted eye cannot see clearly the far object. That aberration happens because the image of the object falls in front of the retina. Nearsighted can be helped by using glasses with a concave lens (a negative lens).
Farsighted Eye (Hypermetrophy)
People who suffer farsighted eye cannot see clearly a near object. It happens because the image falls behind the retina. Although the eye has maximum accommodation, the image of the object still falls behind the retina. A farsighted eye can be helped by using the positive glasses (a convex lens).
The Old Eye (Presbyopia)
This eye aberration occurs because the increasing age makes the accommodation power of the eye decrease. It is called presbyopia. The sufferer of the old eye cannot see clearly the near and far object.
In an old aberration, the near point and the far point has changed. To be able to see the near and far object clearly, it must be helped with bifocal glasses (glasses with double functions: to see near distance and far distance).
The Part Of Human Eye
From the figure below, you can see the complete part of the human eye and their position.
Cornea
Cornea functions in receiving and transmitting the light and also to protect the eye lens from feathers.
Iris
Iris is a membrane in front of the eye lens that forms a circular chink. Iris functions in giving a color of the eye and arranging the intensity of the light entering the eye. There are so many colors of the eye. This color is caused by melanin that contains in the iris.
Pupil
The pupil is the circular chick formed by iris. The wide of the pupil is controlled by iris based on the intensity of the light entering the eye. At dark or dim condition (less light intensity), the iris relaxes so that the pupil enlarged. As a result, more light enters the eye.
At bright condition (high light intensity), the iris contracted so that the pupil becomes smaller. As a result, the light entered to the eye decreases.
Eye Lens
The eye lens is made of transparent material, fibered, and elastic and also convex in shape. The eye lens functions in constructing the image of an object. The image formed by the eye lens similar to the image formed by a convex lens – real, upside down and smaller in properties.
Retina
The retina is the back part surface of the eye. It functions as a screen to catch the image formed by eye lens. The retina consists of yellow grains, which are very responsive to the light.
Eye Nerve
The eye nerve functions in continuing the signals received by the retina to the brain. The brain process and translates the signals so that we can see the object in upright.
From the part of the eye above, now you can know each simple functions of it in seeing process.
The Accommodation Power of Eye
An object (near or far) can be seen clearly because its image formed by the eye lens falls exactly at the retina. Why does the image of an object fall exactly at retina although its distance is change?
The answer is because the eye lens is elastic (it can change to thin of thick shape). Because eye lens can change the shape, its focal length can change according to the need, therefore the image of an object can be arranged to fall exactly at the retina.
The ability of the eye lens, to thicken and to thin in order to produce an image exactly at the retina is called the accommodation power of the eye.
When the eye accommodates maximally, the eye lens thickens. As a result, the focal length of the eye increases. On the other hand, when the eye accommodates minimally, the eye lens becomes thin so that the focal length of the eye decreases.
Because of the accommodation power of the eye, the eye has near point (punctum proximum) and a far point (punctum remotum). A near point is the nearest point of an object to the eye that still can be seen clearly by the eye, which the eye accommodation maximally.
A far point is the furthest point of the object to the eye that still can be seen clearly by the eye, in which the eye does not accommodate. So the eye can see an object clearly if the object is placed between the near point and the far point.
Eye Aberration
A normal eye has a near point at a distance of 25 cm and a far point at a distance of unlimited. If the accommodation power of the eye lens decreases, then it has suffered an eye aberration.
Nearsighted Eye (Myopia)
People who suffer nearsighted eye cannot see clearly the far object. That aberration happens because the image of the object falls in front of the retina. Nearsighted can be helped by using glasses with a concave lens (a negative lens).
Farsighted Eye (Hypermetrophy)
People who suffer farsighted eye cannot see clearly a near object. It happens because the image falls behind the retina. Although the eye has maximum accommodation, the image of the object still falls behind the retina. A farsighted eye can be helped by using the positive glasses (a convex lens).
The Old Eye (Presbyopia)
This eye aberration occurs because the increasing age makes the accommodation power of the eye decrease. It is called presbyopia. The sufferer of the old eye cannot see clearly the near and far object.
In an old aberration, the near point and the far point has changed. To be able to see the near and far object clearly, it must be helped with bifocal glasses (glasses with double functions: to see near distance and far distance).
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