Page 175 - Science Class 08

THE HUMAN EYE the pupil is the eye-lens. The focal length of the

Structure lens is controlled by the eye-muscles. This lens
focusses the image of the object on the re na
The human eye is an organ that carries the
which is like a light-sensi ve film. The re na
sense of sight. Sight is the most precious sense
converts the light rays into electrical visual
and that is why blindness is the most feared
signals that are carried to the brain by the op c
disability. The human eye measures about 2.5
nerve. The brain interprets these signals into
cm in diameter. It has natural lens that is
visual images and the objects is seen.
marvellous indeed. It can adjust its focus
between a distant point and a nearby point. It Three Eye-disorders
can also direct itself towards any object to be There are three common eye-disorders that
seen. It can work in dim light as well as in cannot be cured though they can be overcome
bright light, though not in complete darkness. using eye-glasses or contact lenses.

Ciliary Muscles Lens Selerea Near Sightedness
This disorder is called myopia also. It occurs if
Choroid
Aqueous the light-rays reflected by distant objects meet
Humour Foeva
Blind spot (converge) before they reach the re na. The
Pupil result is that distant-vision is blurred, though
Cornea near-vision is all right.
Op c Nerve
Iris
Re na Concave glasses or contact lenses can set this
Eyelid
Vitreous Hurmour disorder right by making the rays from distant
Conjuc va objects meet at the re na.
Human Eye
Working

Light-rays reflected by the object to be seen
enter the eye through its transparent ssues.
The eye changes these rays into electrical visual
signals and sends it to the brain through the
op cal nerve. The brain interprets them as real
visual images. Myopia

Let us see how it happens:

Func oning of the Human Eye

The coloured part of the eye is called iris while Correc on : Concave lens
its innermost part is called the pupil. Behind

Science-8 175