In the human eye,the image of an object is formed on the $................$.

Why do we observe the seven colours when white light passes through a glass prism? Which component of white light deviates the least?

Presbyopia is a type of far-sightedness.

What is the number of receptors contained in the retina?

$A$ myopic person has been using spectacles of power $-1.00\, D$ for clear vision. During old age,he also needs to use separate reading glasses of power $+2.00\, D$. Explain what may have happened to his eyesight?

Pigments are mixed by the $......$ method to produce various colors.