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Updated on May 26, 2016

The senses which serves to recognize changes in the external environment is called eksoreseptor. There are five type of eksoreseptor. One is the eye (sense of sight) .The human eye is slightly oval-shaped, but we more often call to the eyeball. The eye has a muscle to be able function properly. The muscle is a layer of the eye (consisting of skelra, choroid and retina), and the receptors of the eye. Light will enter into the eye must pass through several layers of cells. The cells are divided into two, the cone cells and stem cells. Cones role for vision in daylight. While stem cells for vision at night. The cone cells sensitive to high light intensity and the stem cells are sensitive to low light. In addition to the shape and structure of the eye, we also have to recognize the disease or abnormality of eye. There are 7 types of eye diseases that must be warrant, namely:

1. Farsightedness (myopia). This is a condition where the eyeball is too long or too convex lens of the eye so that the shadows were right in front of the retina. In order to see normally, people with myopia have to use a concave lens (diverging negative)

2. Short sighted (hipermitropia). Short sightedness caused by the eyeball is too short or the lens of the eye that can not be convex, so that the shadows that go far behind the retina. In order to see normally, hypermetropia sufferers should use a convex lens called (positive convergent)

3. Cataract. If someone is suffering from this disease, his eyes will look bleached almost entirely up to the eyeballs black. This is due to calcification which makes the eye lens becomes opaque and not elastic, so the power is reduced eye accommodation. So that the eye is able to see normally, patients must resort to surgery

4. Presbyopia. These diseases are caused by the elasticity of the eye is reduced because of old age. People with presbyopia can be helped by using two kinds of lenses (lenses copies) in order to see properly

5. Astigatisme. This situation shows the surface of the eye lens is not the same so that the focus of vision was not the same. Shadows that form was also not the same. To treat patients astigatisme, can be a way to use eye lens cylinder

6. Glaucoma. This type of eye disease due to the increase of pressure inside the eye due to fluid that is in the anterior chamber of the eye have not been removed, so that the power of vision is lost due to a voltage that causes pressure on the optic nerve.

The shortest distance between the eye and the object to be visible or recognizable clearly referred to a distant point. Distant point of someone usually different, depending on the age of the person. Of course distance point elderly people far enough away that is about 50 cm. That is why if you want to read books, newspapers, read sms indicated on a cell phone or other readings that small writing, would be kept away from the eyes. To help their eyesight, can the use of positive convex lens


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