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About the eye |
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About the eye |
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The eye works in a similar way to a camera. Light enters the eye and is focused onto the retina which is a light sensitive lining at back of the eye.
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Light travels throught he cornea which partially focuses the image then it travels through the opening inside the iris called the pupil and it is then finely focused by the crystalline lens which can focus the eye for different distances of viewing. This can occur because the lens is flexible and muscles attached to it alter its curvature and hence its power. When this lens gets less flexible with age this ability is reduced and often reading glasses are required. This occurs typically after the age of 40.
The pupil will change its diameter as the volume of light entering the eye causes the iris to constrict or dilate respectively to protect the sensitive retina from too much light entering the eye and causing glare and potential long term damage
The image on the retina is then converted into electrical impulses which then travel along the optic nerve to the part of the brain responsible for light which is called the visual cortex. Visual perception is therefore achieved.
Eye movement is controlled by six muscles around the outside of the eye which work in co-ordination with each other and the other eye to provide binocular single vision. If this does not occur then a squint in childhood develops. If this occurs in adulthood due to injury or disease double vision follow.
The cornea is a curved, highly transparent tissue that separates air from clear fluid in the anterior chamber of the eye, which lies between the cornea and lens.
The lens is a firm gel-like transparent tissue that is almost eight millimeters (one-third inch) in diameter and biconvex in shape, that is, thicker in the center than at the edge. A thin transparent capsule surrounds the lens.
The iris is in front of the lens and consists of a circular pigmented muscle that gives the eye its color. The iris acts like the diaphragm of a camera and adjusts the amount of light that enters the eye through the hole in its center called the pupil. Light then passes through the vitreous, a clear gel-like material that fills the center of the eye, onto the retina.
The retina is the film of the eye. It is a true extension of the brain and is composed of special nerve cells sensitive to light.
The optic nerve is formed from these nerve cells and carries the light image entering the eye to the brain.
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