For a normal eye,the cornea of the eye provides a converging power of $40\, D$ and the least converging power of the eye lens behind the cornea is $20\, D$. Using this information,the distance between the retina and the cornea-eye lens can be estimated to be ......... $cm$.

$A$ person with hypermetropia has a near point of $60\, cm$. What power of lens should be used for the eye to read a book at $25\, cm$?

The near point of a hypermetropic person is $75\, cm$ from the eye. What is the power of the lens required to enable the person to read clearly a book held at $25\, cm$ from the eye?

$A$ person is suffering from the defect astigmatism. Its main reason is

$A$ myopic adult has a far point at $0.1\, m$. His power of accommodation is $4\, D$.
$(i)$ What power lenses are required to see distant objects?
$(ii)$ What is his near point without glasses?
$(iii)$ What is his near point with glasses? (Take the image distance from the lens of the eye to the retina to be $2\, cm$.)

The image formed on the retina of the eye is proportional to: