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Understanding the Human Eye

The human eye is roughly spherical in shape with a diameter of about 2.3 cm. It functions like a camera with a lens and retina. The main parts of the eye include the cornea, iris, pupil, lens, retina, aqueous humour, and optical nerve. The lens allows for accommodation by changing shape via ciliary muscles to focus on near and far objects. Common vision defects include myopia, hyperopia, astigmatism, and color blindness. Myopia occurs when the eyeball is too long and is corrected using concave lenses.

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59 views2 pages

Understanding the Human Eye

The human eye is roughly spherical in shape with a diameter of about 2.3 cm. It functions like a camera with a lens and retina. The main parts of the eye include the cornea, iris, pupil, lens, retina, aqueous humour, and optical nerve. The lens allows for accommodation by changing shape via ciliary muscles to focus on near and far objects. Common vision defects include myopia, hyperopia, astigmatism, and color blindness. Myopia occurs when the eyeball is too long and is corrected using concave lenses.

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kWaNgyA
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Human Eye: working of human eye, Persistence of vision, Power of accommodation

of human eye, Defects of vision.


The Human Eye: It is a natural optical instrument which is used to see the objects by
human beings. It is like a camera which has a lens and screen system.
Structure of the Human Eye
The various parts of eye and their functions :

• Retina: It is a light sensitive screen inside the eye on which image is formed. It
contains rods and cones.
• Cornea: It is a thin membrane which covers the eye trail. It acts like a lens
which refracts the light entering the eye.
• Aqueous humour: It is fluid which fills the space between cornea and eye lens.
• Eye lens: It is a convex lens made of transparent and flexible jelly like
material. Its curvature can be adjusted with the help of ciliary muscles.
• Pupil: It is a hole in the middle of iris through which light enters the eye. It
appears black because light falling on it goes into the eye and does not come
back.
• Ciliary muscles: These are the muscles which are attached to eye lens and
can modify the shape of eye lens which leads to the variation in focal lengths.
• Iris: It controls the amount of li ght entering the eye by changing the size of
the pupil.
• Optical nerve: These are the nerves which take the image to the brain in the
form of electrical signals.
• The human eye is roughly spherical in shape with a diameter of about 2.3 cm.
It consists of a convex lens made up of living tissues. Hence, human lenses
are living organs contrary to the simple optical lenses. The following table
lists the main parts of the human eye and their respective functions.
• The ability of the eye lens to adjust its focal length accordingly as the
distances is called power of accommodation.

olour Blindness: A person having defective cone cells is not able to distinguish
between the different colours. This defect is known as Colour Blindness.
Defects of Vision and their Correction
Myopia (Short-sightedness): It is a kind of defect in the human eye due to which a
person can see near objects clearly but he cannot see the distant objects clearly.
Myopia is due to
(i) excessive curvature of the cornea.
(ii) elongation of eyeball
Correction: Since a concave lens has an ability to diverge incoming rays, it is used to
correct this defect of vision. The image is allowed to format the retina by using a
concave lens of suitable power as shown in the given figure.

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