Lenses are transparent objects that bend (or ‘refract’) light by the curvature of their outer surface. A corrective lens is a lens that is typically worn in front of the eye to improve daily vision. The most common use is to treat refractive errors: myopia, hypermetropia, astigmatism, and presbyopia.
Types of Optical Lenses
Single vision lenses
Single vision lenses have the same prescription power across the entire lens. Ideal for correcting myopia (near-sightedness) and hyperopia (far-sightedness).
Bifocal lenses
Bifocals are made up of two lenses to correct both near and far-sighted vision. Bifocals have a visible dividing line between the two.
Trifocal Lenses
Trifocals are made up of three lenses to correct not only near and far-distance vision, but also presbyopia, the inability to focus in the middle distance (caused by loss of flexibility in the eye’s lens).
Progressive lenses
Progressive lenses are becoming an increasingly popular choice over bifocals and trifocals. Progressive lenses correct vision at near, middle, and far distances with no “transition zone” or visible divide.
Toric Lenses
Toric lenses are a type of single-vision lens used to correct astigmatism by adding cylinder correction, an additional prescription power.
Prism Lenses
Prism lenses correct heterophoria, a vision disorder characterized by the eyes not looking in the same direction when at rest.
Lens Materials
CR-39 Plastic
is a thermal-cured plastic polymer popular because of its low cost and lightweight.
Polycarbonate
was first used to make helmet visors and safety glasses and is now a popular choice for prescription eyeglasses. Polycarbonate is lighter and more impact-resistant than CR-39 plastic.
High-index Plastic
a higher refractive index (how efficiently light passes through the material) than CR-39 plastic, making the lenses thinner and lighter.
Glass
lenses have excellent optical qualities, are scratch-resistant and typically cost less than plastic. Glass lenses are not widely used because they are heavier and break more easily than plastic.
