What is astigmatism?

What is the cuase of astigmatism?

Name the Part that is affected in astigmatism.

Which one of the following lenses should be used to correct the defect of astigmatism?

How the defect of astigmatism can be corrected ?

Collect information about causes and corrections for myopia , hypermetropia , astigmatism, prebyopia , cataract , night blindness.

What is magnetism and what is magnet ?

What is irrigation? What are the types in it?