Convex and concave lenses can both be used to correct defects of vision. The most commonly occurring defects of vision are ‘short sightedness’ and ‘long sightedness’. People who are ...

The two types of concave lenses — biconcave and plano-concave — are negative. Meniscus lenses — a third broad type also referred to as convex-concave — can be either positive or negative, depending on ...