How is astigmatism corrected?

Which part of the eye helps in changing the focal length of the eye lens to focus the image of objects lying at varying distances from the eye?

$A$ person cannot see distinctly objects kept beyond $2\, m$. This defect can be corrected by using a lens of power:

$A$ person cannot see objects distinctly when placed beyond $2\, m$.
$(a)$ Identify the eye defect.
$(b)$ Give two reasons for this defect.
$(c)$ Calculate the power and nature of the lens he should be using to see the distant objects clearly.
$(d)$ Draw the ray diagrams for the defective and the corrected eye.

In the eye of a person suffering from myopia (nearsightedness),where is the image of a distant object formed?

What is the iris?