$A$ defective eye cannot see close objects clearly because their image is formed

The lens used to correct long-sightedness (hypermetropia) is:

If the distance of the far point for a myopia patient is doubled,the focal length of the lens required to cure it will become

$A$ man is suffering from colour blindness for green colour. To remove this defect,he should use goggles of

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

$A$ person wears normal spectacles in which the distance between the glasses and the eyes is approximately $2 \, cm$. The power required is $-5 \, D$. If he wears contact lenses,then the required power is ......... $D$.