The Human Eye Done by: Rashed Khalid – ebraheem nasser Class: 12-2

How Does The Human Eye Work? The individual components of the eye work in a manner similar to a camera. Each part plays a vital role in providing clear vision. So think of the eye as a camera with the cornea, behaving much like a lens cover. As the eye's main focusing element, the cornea takes widely diverging rays of light and bends them through the pupil, the dark, round opening in the center of the colored iris. The iris and pupil act like the aperture of a camera. Next in line is the lens which acts like the lens in a camera, helping to focus light to the back of the eye. Note that the lens is the part which becomes cloudy and is removed during cataract surgery to be replaced by an artificial implant nowadays.

The Camera The Human Eye The very back of the eye is lined with a layer called the retina which acts very much like the film of the camera. The retina is a membrane containing photoreceptor nerve cells that lines the inside back wall of the eye. The center 10% of the retina is called the macula. This is responsible for your sharp vision, your reading vision. The peripheral retina is responsible for the peripheral vision. As with the camera, if the "film" is bad in the eye (i.e. the retina), no matter how good the rest of the eye is, you will not get a good picture. The human eye is remarkable. It accommodates to changing lighting conditions and focuses light rays originating from various distances from the eye. When all of the components of the eye function properly, light is converted to impulses and conveyed to the brain where an image is perceived.

Physics in the human eye In which the object is beyond 2F, and the image formed is real, inverted, smaller than the object, and on the opposite side of the lens. We know that the image formed must be real, because it is projected onto the retina (which is like a screen). Any time an image is projected, it must be real. At the same time, any real image must be inverted. This might make you wonder why you don’t see objects as being upside down. Actually, our brain flips things around so that we see them as being upright.

Anatomy of the eye

Normal Vision The process in which the lens changes its focal length to focus on objects at different distances is called accommodation

Near point and far point The point nearest the eye at which an object can be placed and still produce a sharp image on the retina is called the near point (~ 25 cm from the eye- 20 yr old, 500 cm at age 60) The far point of the eye is the location of the farthest object on which a fully relaxed eye can focus. Normal vision people have a far point of nearly infinity

Nearsightedness

Eyeglasses for the nearsighted—A nearsighted person has a far point located only 521 cm from the eye. Assume eyeglasses ar 2 cm in front of the eye. Find the focal length needed for the diverging lenses of the glasses needed

Farsightedness

To find the height of the image on the retina

The astronomical telescope The Refractor