What is presbyopia:

It is a defect of vision seen in old age, in which a person cannot see nearby objects clearly. The near point moves away from the normal 25 cm.

Main causes:

1. Weakening of the ciliary muscles. With age the ciliary muscles become weak, so they cannot change the shape of the eye lens properly.
2. Loss of flexibility of the eye lens. The eye lens slowly becomes hard and less elastic, so it cannot become thick enough to focus nearby objects.
3. Decrease in the power of accommodation of the eye as a result of the above two changes.

Correction:

• A convex lens is used to see nearby objects.
• If the person also suffers from myopia, bifocal lenses are used — the upper part is concave (for distant vision) and the lower part is convex (for near vision).