For correction of which defects in vision of eye spectacles to convex and concave lenses and used

For correction of which defects in vision of eye spectacles of convex and concave lenses are useD?

Which type of defect of vision is rectified a convex lens?

Convex lenses correct.

What type of lens is used for correction of defect in case of Myopia?

Two lenses, one convex and the other concave are kept in contact. The focal length of convex lens is 30cm and that of concave lens is 20 cm. Whaat will be the equibalent focal length of the combination? What will be the nature of the combination?

A person with defective eyes can see the objects distinctly up to the distance 20 cm . What type of lens should be used and of what power?

A person uses spectacles of power +2D. What type of defect of vision is it?