What is Accomodation of eye? Write various defects of vision and their cause. How the eye of person suffering from nearsightedness and farsightedness may be corrected ?

Explanation

Accomodation :
Various defects of vision are :
(i) Near-sightedness (ii) Far siglitedness (iii) Presbyopia (iv) Astigmatism
(i) Near sightendness (Myopia):
(ii) Far-sightedness (Hypermetropia) :
(iii) Presbyopia :
Cause : Power of accomodation of eye decreases with age due to weakning of ciliary muscles.
(iv) Astigmatism : It is an eye defect due to which a person can not focus on horizontal side and vertical side simultaneously.
Cause : Non-spherical shape of cornea and as a result eye tens of a person has different focal lengths in different planes.
Correction : It can be curved by using cylindrical (non-spherical) lenses.