The human eye can focus objects at different distances by adjusting the focal length of the eye-lens. This is due to:

An eye has a near point distance of 0.75 m. What sort of lens in spectacles would be needed to reduce the near point distance to 0.25 m? Also calculate the power of lens required. Is this eye long-sighted or short � sighted?

An eye has a far point of 2 m. What type of lens in spectacles would be needed to increase the far point to infinity? Also calculate the power of lens required. Is this eye long-sighted or short-sighted?

The defect of vision which cannot be corrected by using spectacles is :

A person cannot see the distant objects clearly (though he can see the nearby objects clearly). He is suffering from the defect of vision called :