There are number of spectacle lens types available including "single vision lens," "progressive lens" and "bifocal lens*."
This type is the spectacle lens normally used for correction of conditions such as nearsightedness, farsightedness and astigmatism and a single lens features a single power. This type of lens is used for ordinary corrective applications and dedicated handy reading spectacles.
Single vision lenses feature a number of designs including spherical, aspheric and Double-sided Aspheric designs, each providing the wearer with a different visual capability and facial fit comfort.
*We do not deal in this type of lens
People with presbyopia using handy dedicated reading spectacles have to use one pair of spectacles to look at objects in the distance and another to view objects nearby.
The multi-focal lens eliminates this irksome procedure by allowing the wearer to see objects both in the distance and at close quarters through a single lens that features a separate portion for each range.
The most common type of multi-focal lens is the bifocal lens which features a single lens for viewing objects at close quarters at the bottom of the lens. In addition, the tri-focal lens features a lens for viewing objects in the intermediate distance as well as the far-sight and near-sight lenses.
The bifocal lens* comprises of a portion for viewing objects in the distance and a segment for viewing objects at close quarters. Objects in the distance and nearby can be viewed from the lines of vision shown in the illustration.
The progressive lens features a consecutive and smooth variation from the long-sight lens power to the near-sight lens power provided by the above multi-focal lens. Because it allows the wearer to see objects nearby, in the distance and in the intermediate distance and also because it is highly fashionable in appearance due to a lack of the conspicuous lines between different prescription areas on the multi-focal lens, the progressive lens is used for correction of presbyopia. Note that the progressive lens comes in a wide variety of types to allow selection of lenses to match the purpose and application.
Objects in the distance, nearby and in the intermediate distance can be seen from the lines of vision shown in the illustration. The broken lines in the illustration are not actually printed on the lens itself.