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Wednesday, 12 December 2018

Structure of the Eye

The most important part of all the parts of the eye are the lens and retina. The wall of the eye ball consists of the layers.

(i) The outermost layer is the Sclera
(ii) The middle layer is the Retina
(i) The sclera : This is the white tough layer which protects and maintains the shape of the eyeball. It bulges out in front to form the transparent cornea. The cornea keeps dust and dirt from passing through the pupil of the eye.

    The back of it is perforated by the optic nerve. This is the message sending nerve from the eye to the brain.

    The eye lids are thin membrane which close to protect the eyes from the foreign objects.

(ii) Choroid : Consists of black pigmented cells. In front, it front,  it forms the muscular ciliary muscles which hold the lens in position. The lens is a transparent glass like structure which focuses the light rays on one spot of the retina, thus forming the image. The space in front of the lens is filled with watery aqueous humour. The bigger space behind the lens is filled with vitreous humour. These helps to maintain the spherical shape of the eyeball. The Iris is the coloured part of the eye surrounding the pupil. It can increase or decrease the size of the pupil. The hole at the center of the iris is called the pupil. Light enters the eye through the pupil.

(iii) The retina : is the light sensitive spot at the back of the eyeball. the most sensitive part of the retina is the blind spot. The eyebrow prevents sweat from running into the eyes. the eyelashes protect the eyes from dust and dirt. The tear gland pours out over the eyes washing any dust that enters the eyes.

How can we see when we look at objects:

    The light rays from which point of the object enter our eye. As they pass through the cornea, aqueous humour, lens and vitrous humour, they are bent and brought to focus on the retina to form an image. This image is real, smaller but inverted. The impulse of the image is sent to the brain through the optic nerve. the brain now tells that the object is upright, gives the real size and distance of the object. we therefore see the object as it is and not as image is formed at the retina.
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