HUMAN ANATOMY AND PHYSIOLOGY

ASTIGMATISM ::

It is an error or refraction where rays are not sharply focussed on the retina it results from oblong shape of the cornea and the lens Thus the curve of one plane differs from that of the other plane Here the rays of one plane (vertical) and another (horizontal) do not come to a common point of focus on the retina This error is corrected by cylindrical lens or by combining cylindrical and spherical lenses This correct and sharp image 

CATARACT ::

Cataract results from an opacity of the lens It is generally due to degenerative changes in old age This condition can be treated surgically by removing the lens Following surgery the patient may have to wear very thick lenses however some people are able to wear contact lenses Frequently people have difficulty in judging distances at first and must be particularly cautious in walking up and down the stairs Now a days an artificial transparent plastic lens intra ocular lense (10L) can be fifted permanently in its place by opthalmic surgeon Even for removal of cataract lens laser is used to break the lens and then is sucked out This is called Pheco surgery