Which of the following eye defects is caused by the inability of the eye to focus light on the retin

In a normal eye, the lens bends light so it meets exactly on the retina, the light-sensitive screen at the back of the eye. Myopia, or short-sightedness, happens when the eyeball is too long or the lens bends light too strongly, so the light meets in FRONT of the retina instead of on it. Far objects then look blurred, while near objects are still clear.

Because the fault is in where the light is focused, myopia is corrected with a concave (diverging) lens, which spreads the rays slightly so they land on the retina.

The other defects are different problems. Glaucoma is a build-up of pressure inside the eye that damages the optic nerve. A cataract is a cloudy lens that blocks light from passing through clearly, rather than mis-focusing it. Astigmatism comes from an uneven cornea that blurs the image in one direction.