(i) Myopia is corrected using spectacles containing concave lenses. The whole purpose of using concave lenses is to reduce the converging power of the eye lens and hence helping in forming the image of the distant object on the retina of the myopic eye.

(ii) Presbyopia defect is corrected using the spectacles containing convex lenses. The whole purpose of using concave lenses is to increase the converging power of the eye lens and hence helping in forming the image of the nearby object on the retina of the myopic eye.