Why do we have two eyes for vision instead of just one?

List four common defects of vision that can be corrected with the use of spectacles.

When do we consider a person to be myopic or hypermetropic? Explain how the defects associated with a myopic and hypermetropic eye can be corrected.

What is the range of clear vision for a person with normal vision?

$A$ person cannot see objects distinctly when placed at a distance less than $50\, cm$.
$(a)$ Identify the defect of vision.
$(b)$ Give two reasons for this defect.
$(c)$ Calculate the power and nature of the lens he should be using to see clearly the object placed at a distance of $25\, cm$ from his eyes.
$(d)$ Draw the ray diagrams for the defective and the corrected eye.

Study the diagram given below and answer the questions that follow it.
$(i)$ Identify the defect of vision represented in this case. Give a reason for your answer.
$(ii)$ Mention the two causes of this defect.