Difference between Hypermetropia and presbyopia

Difference between Hypermetropia and presbyopia

Hypermetropia

  1. The defect in human eye in which one can see distinct objects clearly, but cannot see nearby object clearly is known as hypermetropia or far sightedness.
  2. In Hypermetropia, ciliary muscles contracts the lens, but doesn’t relaxed, so that the focal length of eye lens increases, eyeball gets flattered.
  3. Image of object forms behind retina due to divergence of rays after retina since the focal length is increased.
  4. This makes person able to see distinct objects clearly but can’t make him/her able to see nearby objects.
  5. To correct this defect, an ophthalmic doctor prescribes the convex lens of suitable power (or focal length) to use in spectacles.
  6. Hence the power of lens for the person with hypermetropia is positive.

Presbyopia

  1. The defect of human eye which is appears due to old age is known as presbyopia.
  2. The power of accommodation of eyes decreases due aging so the person finds difficulties in seeing nearby objects as well as distinct objects.
  3. Such people require bi-focal lenses.
  4. A bi-focal lens is combination of both concave and convex lenses.
  5. The upper portion consists of a concave lens and lower part is convex lens, so that both the difficulties in vision of nearby as well as distinct object can be easily overcome.
  6. Hence the power of lens of person with presbyopia is positive as well as negative.
Updated: September 30, 2021 — 11:34 am

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