Question

A person may suffer from both myopia and hypermetropia defects.

(a) What is this condition called?

(b) When does it happen?

(c) Name the type of lens often required by the persons suffering from this defect. Draw a labeled diagram of such lenses.

Answer 1

Eye defects:

1. The human eyes gradually lose their power of accommodation.
2. In such cases, the person cannot see distinctly and comfortably.
3. There are three common eye defects, and they are(i) myopia or near-sightedness, (ii) Hypermetropia or far-sightedness, and (iii) Presbyopia.
4. These defects are corrected by the use of suitable spherical lenses.

(a) Presbyopia:

1. This condition is called presbyopia.
2. Myopia, a common visual disease known as nearsightedness, causes fuzzy vision for items that are far away but clear vision for nearby objects.
   1. It happens when light rays improperly bend (refract) due to the shape of our eye, focusing pictures in front of our retina rather than on our retina
3. Other names for hypermetropia include hyperopia, long-sightedness, and far-sightedness.
   1. The eye disease known as hypermetropia is characterized by the formation of an image of a close object behind the retina.
   2. Instead of concentrating on the retina in this instance, the light is concentrated behind the retina.
4. Presbyopia is the slow loss of our eye's ability to focus on nearby objects.
   1. Presbyopia becomes noticeable in the mid-40s and continues to worsen until around age 65.
   2. The vision appears to be blurred, due to the loss of power of accommodation of the eye.
   3. The near point of the presbyopic eye recedes gradually and becomes much more than 25 cm away.

(b) This defect occurs in old age due to the gradual weakening of the ciliary muscle and the eye lens becoming inflexible (or rigid).

1. The ciliary muscle gradually weakens and the eye lens becomes hard as people age, resulting in this condition (or rigid).
2. Therefore, the eye loses its power of accommodation.
3. It is corrected in the same way as hypermetropia by using spectacles containing convex lenses.

(c) Bifocal lens:

1. A bifocal lens is often required by persons suffering from this defect.
2. It is also possible that a person may suffer from both the defect of vision – myopia as well as hypermetropia.
3. Therefore, these person uses spectacles having bifocal lenses in which the upper parts consist of a concave lens (to correct myopia) used for distant vision and the lower part consists of a convex lens (to correct hypermetropia) used for near vision.