SINGLE VISION LENSES: These lenses have the same power through the whole lens. They are often the first type of lens children or teenagers have if they are short-sighted or far-sighted enough to need glasses. At that age, usually a single power lens is all that is needed for all visual tasks. Separate reading or computer distance lenses can fall into this category also. Advantage: You have the entire lens to look through for the intended task.
BIFOCAL LENSES: These lenses are most commonly used by adults over the age of forty – the age when most people start to have difficulty focusing on near work. They have two distinct powers. The top part of the lens is the distance power and the bottom segment, separated by a visible line, contains the reading power. They eliminate the need for two separate pairs of glasses – one for reading and one for distance. They have largely been replaced by the newer progressive lenses.
Advantage: Because of the line, you know exactly which part of the lens to look through.
PROGRESSIVE LENSES: Also called MULTIFOCAL lenses, the progressive lens has the distance power at the top of the lens and then slowly changes to the maximum prescribed reading power at the bottom of the lens without any lines. The advantage of this design is that it provides the in-between powers for the in-between working distances – such as arm’s length for computer screens or while standing at a counter. There is usually an adaptation period when wearing the progressive lens for the first time.
Advantage: Because of the range of powers in this lens, it is the closest thing to your natural vision, and the best option if you want one pair of glasses that will do a bit of everything.
Some of the Lesser Known Lens Types:
COMPUTER OR BUSINESS LENSES: This lens is a form of progressive lens but without the distance component. The powers for detailed close work and arm’s length computer use are larger than in the full progressive lens, resulting in a more comfortable lens for extended reading and computer tasks. The computer power is also centred in front of your eyes, eliminating the need to raise your chin to see through the bottom of the lens while working at the computer.
Advantage: Covers a range of near visual tasks more comfortably than other lens options.
“ANTI-FATIGUE” LENSES: These lenses have also been developed for computer users, but for younger people who don’t yet require bifocals or progressive lenses. They are similar to a progressive lens but with just a hint of reading power at the bottom of the lens to alleviate some of the stress of long hours of computer, smart phone or hand-held video game use Advantage: Comfort-oriented lenses that address the problem of “computer vision syndrome” in the high tech world in which we now live and work .
TRIFOCALS AND OCCUPATIONAL QUADRIFOCALS: These lenses are similar to bifocal lenses, with the addition of one or two more sections for close work. The trifocal adds another segment, directly above the bifocal segment, that contains a power mid-way between the distance and reading prescriptions, for seeing approximately at arm’s length. Occupational quadrifocals add yet another segment in the top part of the lens with a similar power to the trifocal, for tasks requiring close work above eye level, such as putting up drywall or painting overhead. Advantage: Covers a range of different working distances without having to switch glasses.