Corrective lenses work by refraction: they bend light rays as they pass through them, so they change direction. That means the rays seem to come from a point closer or further away from where they originate—and that’s what makes objects seen through a lens seem either bigger or smaller than they really are. Light focuses on the correct part of the retina, bringing an image into clarity.
There are primarily two types of corrective lenses today: eyeglasses and contact lenses.
Like eyeglasses, contact lenses correct refractive errors. They do this by adding or subtracting focusing power to the cornea and lens.
A lens is an optical tool or device that tends to both converge and diverge a beam of light.
A simple lens usually consists of only a single piece of transparent material.
Categories of simple lenses:
1. Convex lenses (sometimes called positive lenses). This lens type is thicker at the center and thinner at the edges. It bends light inward to correct farsightedness.
2. Concave lenses are shaped round inwards at the center and bulge outwards through the edges (lenses that cave inward). They are used to treat myopia as they make faraway objects look smaller than they are.
A compound lens is a lens made of simple lenses mounted on a common axis usually in placing two elements close together or side by side and often cemented together.