explain the construction & working of human eye with labelled diagram
Answers
STRUCTURE OF HUMAN EYE AND ITS WORKING
The human eye has been called the most complex organ in our body. It is amazing that so small can have so many parts. Eye is a natural optical instrument. It is present in the form of eyeball in the sockets of our skull. Its diameter is approximately 2.5 cm.
Three layers of eye ball:
Outermost layer – Sclera
Middle layer – choroid
Innermost layer – retina
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Sclera:
It is the outermost, white, tough layer. It covers the whole part of the eyeball. It protects the eyeball. The front portion of the sclera is known as cornea.
Cornea:
Cornea is covered by a thin, transparent membrane known as conjunctiva. Conjunctiva helps the eye to be moist and prevent the dryness.
Choroid:
It is the middle layer of the eyeball. It is made up of connective tissue. It is red brown in color. It provides the nutrition to the eye.
Iris:
It is circular, colored area of the eye that surrounds the pupil. It is found in different colors like brown, black, blue, green, etc.Function of Iris:
It controls the amount of light that enters the eye.
Pupil:
It is an aperture which enlarges and shrinks like a diaphragm of a camera lens.
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Function of Pupil:
It allows the light to enter through the eye lens.
IMPORTANT POINTS :
The iris allows more light into the eye when environment is dark and allows less light into the eye when environment is bright.
The size of pupil is control by the action of papillary sphincter muscle and dilator muscle.
Eye lens:
Behind the iris, there is a transparent biconvex structure holed by cilliary muscles are known as eye lens.
Function of eye lens:
It helps to focus the light on the retina.
Cilliary muscles:
It holds the eye lens and adjusts the focal length of the eye lens so that any object can be seen clearly.
Retina:
It is the innermost layer of the eyeball. Retina contains blood vessels that nourish them. Retina also has two types of photoreceptors: rods and cones.
The most sensitive part of retina is a small area known as Macula where millions cones are tightly packed.
Important Points:
High density of cones in macula makes the visual images detailed.
types of photoreceptoRs
There are two types of photoreceptors:
Cones:
Cones are responsible for sharp, detailed central and color vision. They are mainly clustered in macula. These cells are less sensitive to light.
Rods:
Rods are responsible for night and side vision. These cells are more sensitive to light. These are mainly clustered in peripheral areas of the retina.
Answer: The human eye is a roughly spherical ball with a diameter of around 2.5 cm. Its topmost layer is made of sclerotic, a strong and opaque white material.
Explanation:
The human eye is a roughly spherical ball with a diameter of around 2.5 cm. Its topmost layer is made of sclerotic, a strong and opaque white material. Sclerotic maintains the form of the eye and protects it from external harm.
1. The cornea is the transparent region of the sclerotic that is somewhat bulged outwards.
2. Below the selerotic layer comes a layer of dark tissues known as the choroid. It absorbs any stray light and hence prevents visual blurring caused by reflection from the eye ball.
3. In front of the eye, the choroid combines into a coloured diaphragm known as the iris, which has a hole in the centre known as the pupil.
4. The colour of a person's eyes is referred to as the colour of the person's iris. In bright light, the pupil contracts to admit less light, but in low light, the pupil dilates to admit more light. It stretches to allow as much light in as possible.
5. A crystalline lens with jelly-like layers lies behind the iris. The ciliary muscles serve to keep the lens in place. The lens separates the eyeball into two chambers: the anterior chamber (between the lens and the retina) and the posterior chamber (between the lens and the retina).
6. The anterior chamber is filled with aqueous humour, whereas the posterior chamber is filled with vitreous humour, a jelly-like material.
7. The retina is an extremely sensitive membrane that covers the innermost layer of the eye, covering the whole of the inner surface. It is densely packed with blood vessels and nerve fibres and functions as a light-sensitive screen for receiving pictures.
8. The sense of vision in the retina is transmitted to the brain via the Optic nerve.
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