$A$ person needs a lens of power $-5.5$ dioptres for correcting his distant vision. For correcting his near vision he needs a lens of power $+1.5$ dioptre. What is the focal length (in $cm$) of the lens required for correcting distant vision?

$(a)$ State two main causes of a person developing near-sightedness (myopia). With the help of a ray diagram, suggest how this disability can be corrected.
$(b)$ The far point of a myopic person is $150 \ cm$ in front of the eye. Calculate the focal length and power of the lens required to enable him to see distant objects clearly.

What is the eye lens made of?

What is the cornea?

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

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