How can lens correct these vision defects?

Lenses correct vision defects by altering the path of light entering the eye, ensuring that images are focused properly on the retina. For nearsightedness (myopia), concave lenses diverge light rays, moving the focal point back onto the retina. For farsightedness (hyperopia), convex lenses converge light rays, bringing the focal point forward onto the retina. Additionally, astigmatism is corrected with cylindrical lenses that compensate for uneven curvature of the cornea or lens.