Q.What is hypermetropia? What is its cause and how can it be corrected? Explain with a proper diagram. (1+1+1) OR What is normal adjustment? An astronomical telescope, when in normal adjustment has magnifying power 5. If the distance between two lenses is 0.24 m, find the focal length of both the lenses. (1+2)

In myopia the eye's image of a distant object forms before the retina (due to an elongated eyeball or excessive curvature of the lens); a concave lens diverges the incoming rays just enough to shift the image back onto the retina.

Myopia (short-sightedness/near-sightedness)

Myopia is a common defect of vision in which a person can see nearby objects clearly, but distant objects appear blurred.

Cause: This happens because the image of a distant object is formed in front of the retina, not on it — either because (i) the eyeball has become too elongated (increased length), or (ii) the eye lens's focal length is too short (its converging power is too great), so light from a distant object converges before reaching the retina.

A myopic eye also has a far point that is nearer than infinity — i.e., it cannot see objects placed at very large distances clearly.

…

Hypermetropia is far-sightedness caused by a shortened eyeball or reduced converging power of the eye lens; a convex lens corrects it by converging the light a little before it enters the eye.

What is hypermetropia?

Hypermetropia, also called long-sightedness or far-sightedness, is a common eye defect in which a person can see distant objects clearly but cannot see nearby objects distinctly. It occurs because:

• the eyeball has become too small (axially too short), or
• the focal length of the eye lens is too long (the ciliary muscles cannot increase the eye lens's curvature/power enough).

As a result, the image of a nearby object is formed behind the retina instead of exactly on it, producing a blurred image. The near point of the eye shifts farther away from the eye than the normal near point of 25 cm.

Correction: …