The focal length of the eye lens increases when eye muscles

$A$ person suffering from an eye defect uses lenses of power $-1 \,D$. Identify the eye defect. Draw a suitable diagram to illustrate how this type of lens corrects the defect. Give the nature of the corrective lens to be used. Also,calculate the focal length of the corrective lens.

$(a)$ Explain the following terms used in relation to defects of vision and corrections provided for them:
$(i)$ Myopia $(ii)$ Astigmatism $(iii)$ Bifocal lenses $(iv)$ Far-sightedness (Hypermetropia).
$(b)$ Describe with a ray diagram how a person with myopia can be helped by spectacles.

To correct astigmatism,we use a cylindrical lens.

Which liquid fills the space behind the cornea?

$A$ 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?