Question

Due to gradual weakening of ciliary muscles and diminishing flexibility of the eye lens a certain defect of vision arises. Write the name of this defect. Name the type of lens required by such persons to improve the vision. Explain the structure and function of such a lens.

Answer 1

Q. Due to a gradual weakening of ciliary muscles and diminishing flexibility of the eye lens a certain defect of vision arises. Write the name of this defect. Name the type of lens required by such persons to improve the vision. Explain the structure and function of such a lens.

____________________

Ans. Presbyopia arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the crystalline lens.

Presbyopia is a progressive form of far-sightedness that affects most people with ageing. The power of accommodation of the eye decreases.

The type of lens required by such person to improve the vision is the bifocal lens.

A bifocal lens consists of both convex lens and concave lenses. The convex lens used in the bifocal lens is used to correct hypermetropia (far sightedness) and a concave lens is used to correct myopia (short sightedness).

Answer 2

The defect caused due to gradual weakening of the cillary muscles and diminishing flexibility of eye lens is Presbyopia.

• Presbyopia is a progressive form of farsightedness and affects people with ageing. The accommodation power of the eye decreases with time.  
• The type of lens required by a person suffering from presbyopia is a bi - focal lens. The lens consisting of both the convex lens and a concave lens is a bifocal lens.
• In a bifocal lens the concave lens is used to treat myopia, and the convex lens is used to correct hypermetropia.