This is a piece of glass or plastic (a transparent material) with curved sides for concentrating or dispersing light rays and used to correct vision problems such as long sightedness and near sightedness. They are designed in either convex (thicker at the center) and concave (thicker at the edges).
There are three types of lenses
- Single vision lenses:
These are lenses designed to correct long sightedness, near sightedness and astigmatism.
They come in clear lenses, photo chromatic lenses, antiglare lenses and blue coating lenses.
- Bifocal or trifocal lenses:
These are lenses which has either two or three focal points. A lens is mounted or attached to the other to provide double vision. They offer distance vision and near vision. Bifocals has one noticeable line while a trifocal has two noticeable lines at the centers.
- Progressive or varifocal lenses:
These are lenses which has three invisible segments within. They offer multiple vision i.e. far vision, intermediate and near vision. These lenses possess distortions on the farthest parts of their edges which makes vision blurry.
Most of these lenses has made people to run away from bifocals or trifocals which in turn make them feel old.
Photo chromatic lenses: These lenses work by changing from clear to dark with light intensity from inside to outside. Mostly protecting the eyes against UV light rays from the sun.
Antiglare lenses: Also known as anti reflective coating (AR), these are lens coatings which enhances/improves vision clarity and at the same time eliminates or reduces glares; mostly from artificial light sources.
Blue block lenses: These lenses filters out harsh blue light that one gets from computer screens, LED lights and other digital devices.