Construction of an Eye

Construction Of Eye: The eye performs three functions: it makes adjustments to admit appropriate amount of light, it bends the rays of light to form a sharp image, and it collects and sends information about the image to the brain for further 'processing. Eye allow to learn more about the surrounding world that we do with any of the other four senses. Different parts of the eye perform these functions. The figure shows schematically the basic components of the human eye.

The different parts of the eye are contained within the spherical eyeball, which is about 2.5 cm in diameter. An opaque, white, protective membrane called the sclera covers most of the outer part of the eyeball and is known as white of the eye. A small portion at the front of the eyeball bulges out. A transparent protective membrane called the cornea covers this portion.

The choroid, is the vascular layer of the eye, containing connective tissues, and lying between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye (at 0.2 mm), while in the outlying areas it narrows to 0.1 mm.

Behind the cornea the major structures of the eye consists of

Iris: It controls the amount of light entering the eye by changing the size of the pupil.Pupil is the hole int he middle of the iris through which light enters the eye.

Crystalline Lens: It helps in bending light.It is a convex lens made up of transparent and jelly like material. The size of its curvature can be adjusted witrh help of ciliary muscles.These are the muscles which are attached to the eye lens and leads to the variation in the focal length of the lens. The lens divides the eye into two chambers. The smaller of these two is between the cornea and the lens. It is filled with a watery fluid called the aqueous humour. The larger chamber, between the lens and the retina, is filled with jellylike fluid called the vitreous humour. This fluid helps in maintaining the shape of the eyeball.

Retina: It is a light sensitive screen inside the eye on which the image is formed. It contains rod and cone cells for recognisisng different colours.

Optical nerves:These nerves which take the image to the brain in the form of electrical signals.

Sample Questions

(More Questions for each concept available in Login)

Question : 1

The number of cones in the human eye is _________ the number of rods.
A. More than		B. Less than
C. Equal		D. None of these
Right Option : B
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Question : 2

In the human eye, the opaque diaphragm behind the cornea is called the _____________.
A. Choroids	B. Iris	C. Retina	D. Lens
Right Option : B
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Question : 3

The combination responsible for admitting different amounts of light into the eye is _______________.
A. Ciliary muscles and crystalline lens	B. Ciliary muscles and pupil	C. Iris and pupil	D. Rods and cones
Right Option : C
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