Power of accomodation

Power of accommodation of human eye

Power of accomodation

  • The ability of the human eye to adjust itself such that it can see objects which are nearby and faraway is called Accommodation.
  • It primarily involves the lens and ciliary muscles.
  • The ciliary muscles are capable of modifying the curvature of the lens and thereby affecting the focal length of the lens.
  • When viewing objects which are nearby, the ciliary muscles contract, the lens becomes thicker. It is squeezed into a more convex shape and the focal length decreases (curvature increases). The images again falls on the retina. Note that here the eye is ‘accommodating’ by taking a thicker shape so that the image falls on the retina.
  • When viewing objects which are far away, the ciliary muscles expand, the lens becomes thinner. It is relaxed/loosened into a less convex shape and the focal length increases (curvature decreases). The images again falls on the retina. Note that here the eye is ‘accommodating’ by taking a thinner shape so that the image falls on the retina.
  • However, the focal length of the eye cannot be reduced below a certain minimum limit. If you read a book very close to your eye, it will appear blurred. The minimum distance, at which objects can be seen most distinctly without strain is called the ‘Least Distance of Distinct Vision’ or the ‘Near point of the eye’. For a young adult with normal vision, the near point is about 25cm.
  • The farthest point upto which the eye can see objects clearly is called the ‘Far point of the eye’. For a normal eye, it is infinity.

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