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Chapter 13.3 Optics of Vision

BOOK TITLE: Understanding Medical Physiology: A Textbook for Medical Students

Author
1. Bijlani R.L.
ISBN
9788180612213
DOI
10.5005/jp/books/10999_89
Edition
3/e
Publishing Year
2004
Pages
5
Author Affiliations
1. All India Institute of Medical Sciences, New Delhi
Chapter keywords
vision, refraction, cornea, aqueous humour, plano-convex lens, diopters, dioptric power, stroma, Presbyopia error, diffractive error

Abstract

This chapter discusses optics of vision, where refraction first takes place due to the cornea. The cornea together with the aqueous humour behind it behaves like a plano-convex lens of about 40 diopters. Normally, when a person shifts his sight from a distant object to a near object, there is involuntary increase in the dioptric power of the eye. On the outside, the stroma is lined with the Bowman\'s membrane and epithelium. Bowman\'s membrane is only a less ordered region of the stroma. The structure of the cornea presents at least two characteristics which account for the transparency of the cornea. The lens is transparent due to reasons somewhat similar to those responsible for the transparency of the cornea. The pupil is an adjustable gap in the iris which admits varying amounts of light into the eye. Although a narrow pupil provides a good depth of focus, too narrow a pupil gives a diffractive error. Eye is a sphere barely an inch in diameter with arrangements for forming precisely focussed images of objects at distances varying from a quarter of a meter to infinity. Presbyopia error is generally seen after the age of forty, and becomes progressively worse with age.

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