Page 169 - NCERT Science Class 10 English Medium

weakening of the ciliary muscles and diminishing flexibility of the
eye lens. Sometimes, a person may suffer from both myopia and
hypermetropia. Such people often require bi-focal lenses. A common
type of bi-focal lenses consists of both concave and convex lenses.
The upper portion consists of a concave lens. It facilitates distant
vision. The lower part is a convex lens. It facilitates near vision.
These days, it is possible to correct the refractive defects with
contact lenses or through surgical interventions.

Q U E S T I O N S

1. What is meant by power of accommodation of the eye?
2. A person with a myopic eye cannot see objects beyond 1.2 m distinctly.
What should be the type of the corrective lens used to restore proper
vision?
3. What is the far point and near point of the human eye with normal ?
vision?
4. A student has difficulty reading the blackboard while sitting in the last
row. What could be the defect the child is suffering from? How can it be
corrected?

Think it over

You talk of wondrous things you see,
You say the sun shines bright;
I feel him warm, but how can he
Or make it day or night?
– C. CIBBER
Do you know that our eyes can live even after our death? By donating our eyes after we
die, we can light the life of a blind person.
About 35 million people in the developing world are blind and most of them can be
cured. About 4.5 million people with corneal blindness can be cured through corneal
transplantation of donated eyes. Out of these 4.5 million, 60% are children below the
age of 12. So, if we have got the gift of vision, why not pass it on to somebody who does
not have it? What do we have to keep in mind when eyes have to be donated?

n Eye donors can belong to any age group or sex. People who use spectacles, or those
operated for cataract, can still donate the eyes. People who are diabetic, have
hypertension, asthma patients and those without communicable diseases can also
donate eyes.

164 Science

2024-25