By:Khalid AlNeaimi & Ahmad al sharhan Human Eyes By:Khalid AlNeaimi & Ahmad al sharhan

how does the eye work analogous to a camera? The manner in which the eye works analogous to a camera is elucidated herewith by taking into consideration the entire process of eyesight being perceived, from the time light reflection, refraction and emission by varied items located around occurs and would reach surface of the eyes. Pathway of the light ray is tracked further within.

Nearsightedness Nearsightedness is when light entering the eye is focused incorrectly, making distant objects appear blurred. Nearsightedness is a type of refractive error of the eye . If you are nearsighted, you have trouble seeing things that are far away.

Causes of Nearsightedness People are able to see because the front part of the eye bends which refracts light and points it to the back surface of the eye, called the retina. Nearsightedness occurs when the physical length of the eye is greater than the optical length. This makes it more difficult for the eyes to focus light directly on the retina. If the light rays are not clearly focused on the retina, the images you see may be blurry. Most eyes with nearsightedness are healthy, but a small number of people with severe myopia develop a form of retinal degeneration.

Treatment Wearing eyeglasses or contact lenses can help shift the focus of the light image directly onto the retina, producing a clearer image. The most common surgery to correct myopia is LASIK which stands for (Laser-Assisted In Situ Keratomileusis; Laser vision correction) . Where there gone use excimer laser is used to reshape (flatten) the cornea, shifting the focus.

Farsightedness Farsightedness is greater difficulty seeing near objects than distant objects.

Cause of Farsightedness Farsightedness is the result of the visual image being focused behind the retina rather than directly on it. It may be caused by the eyeball being too small or the focusing power being too weak.

Treatment Farsightedness is easily corrected with glasses or contact lenses. Surgical techniques are available for correcting farsightedness and can be used for those who do not wish to wear glasses or contacts.

Astigmatism Astigmatism is a type of refractive error of the eye. Refractive errors cause blurred vision and are the most common reason why a person goes to see an eye professional.

Cause of Astigmatism People are able to see because the front part of the eye is able to bend (refract) light and point it to the back surface of the eye, called the retina. Changes in the length of the eye, or the shape of either the lens or the cornea make it more difficult for the eyes to focus light. If the light rays are not clearly focused on the retina, the images you see may be blurry. With astigmatism, the cornea (the clear tissue covering the front of the eye) is abnormally curved, causing vision to be out of focus. The cause of astigmatism is unknown. It is usually present from birth, and often occurs together with nearsightedness or farsightedness. Astigmatism is very common. It sometimes occurs after certain types of eye surgery, such as cataract surgery.

Treatment Mild astigmatism may not need to be corrected. Glasses or contact lenses will correct astigmatism. Laser surgery can help change the shape of the cornea surface to correct astigmatism, along with nearsightedness or farsightedness.

What kind of lens we need for Nearsightedness, Farsightedness and Astigmatism ? Concave are diverging lenses, used as spectacle lenses for the nearsighted people. The lens of your eye is a double convex lens. Its job is to focus the image on the retina of the eye. If one is farsighted, the lens in the eye causes the focus to be behind the retina. These people see far but have some difficultly seeing close-up. Contact Lenses are used for Astigmatism which are convex lens.

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Sources http://www.pasadenaeye.com/faq/faq15/faq15_text.html http://www.pasadenaeye.com/faq/faq15/faq15_text.html http://www.livescience.com/3919-human-eye-works.html http://bodyandhealth.canada.com/condition_info_details. asp?disease_id=94