What is the near point of a normal human eye (in $cm$)?

Which part of the eye is responsible for changing the focal length of the eye lens by adjusting its thickness?

$A$ child sitting in a classroom is not able to read clearly the writing on the blackboard.
$(a)$ Name the type of defect from which his eye is suffering.
$(b)$ With the help of a ray diagram show how this defect can be remedied.

The focal length of the eye lens can be changed due to the action of $......................$.

$(i)$ Calculate the maximum power of accommodation of a person having normal vision.
$(ii)$ $A$ person needs to use glasses for reading a newspaper. Identify the defect in her vision and the type of lens she would need to correct it.
$(iii)$ Sometimes when we enter a dark room from bright sunlight,we are unable to see objects clearly. Why?

What is astigmatism?