Single Vision Lenses, as the name implies, have only one power which can be set for distance, intermediate or near focus. In a younger patient this lens will actually work for all distances. For anyone requiring a bifocal/multifocal prescription the lens will be more limited in function as it only has one focus distance
Bi-Focal & Tri-Focal
Bi-Focal lenses have two distinct powers in the same lens and are used by patients so they do not have to switch between two pair of spectacles. Typically they are used in a condition called presbyopia in which the eye loses the ability to focus from distance to near. A bifocal lens has two distinct divisions with the top of the lens set for the distance vision and the bottom for near (reading). In some cases the top of the lens can be made for intermediate distance (computer) and the bottom for near. The transition point where the two powers meet results in a clearly visible "line" which is commonly associated with the bifocal.
Tri-Focal lenses have the same characteristics as Bi-Focal lenses with the addition of an intermediate power range with another visible "line" between the powers.
Progressive lenses are a true multi-focal lens. They provide a smooth, full range of vision. This lens is the most commonly used lens today for patients that require lenses that provide distance, intermediate and near powers at the same time. As with the bifocal and trifocal it is used to correct presbyopia but unlike the later two it does so with a lens design that has no visible lines. To achieve this "no-line" design the change in power is progressive rather than abrubt. The advantage of a progressive lens is that they allow clear viewing at all distances in a cosemetically pleasing way. At Exact Eye Care we use the latest progressive lens designs to maximize your vision.