Question

Name the type of lenses required by the persons for the correction of their defect of vision called presbyopia. Write the structure of the lenses commonly used for the correction of this defect giving reason for such designs.

Answer 1

Type of Lenses Required for Presbyopia

Persons suffering from presbyopia typically require:

• Bifocal lenses
• Progressive lenses (Varifocal lenses)

Bifocal Lenses

• Have two distinct optical powers.
• Upper part: Usually a concave lens or less convex to correct myopia (difficulty in distant vision), or may be plano (no power) if distant vision is normal.
• Lower part: Convex lens to correct hypermetropia (difficulty in near vision).
• Used primarily for presbyopia caused by aging-related weakening of ciliary muscles and reduced lens flexibility.

Progressive Lenses (Varifocals)

• Provide a gradual transition in lens power from top to bottom — no visible segment lines.
• Top portion: For distant vision
• Middle portion: For intermediate vision (e.g., computer work)
• Bottom portion: For near vision (e.g., reading)

Reason for Design

Presbyopia is an age-related condition where the eye loses its ability to focus on nearby objects due to weakening ciliary muscles and reduced lens flexibility. Individuals may also have coexisting refractive errors like myopia or hypermetropia.

Bifocal and progressive lenses are specially designed to:

• Provide clear vision for both near and distant objects
• Accommodate dual or multiple vision needs without needing separate pairs of glasses

Quick Summary:

• Type: Bifocal / Progressive lenses
• Design:
  • Upper segment → Distant vision (concave or less convex)
  • Lower segment → Near vision (convex)
• Purpose: To correct presbyopia and associated dual vision impairment