The older we get the more our eyesight deteriorates. This natural development is called age sight degradation, or presbyopia, and effects everyone sooner or later. Basically the muscles in our eyes begin to gradually weaken and the focusing lenses in our eyes, also called crystal lenses, become staler and less elastic. This weakening can be re-adjusted with the help of spectacles, multi-focal (bi-focal or tri-focal), or progressive contact lenses. These lenses enable us to readjust the capacity of our eyes to optically appreciate our surroundings, near and far.
There are three different means of reconfiguring age sight degradation: through progressive lenses, multi-focal lenses, or through applying a treatment called monovision.
Bifocal lenses function more or less like traditional spectacles. Bifocal lenses enhance the visual capacity of the user particularly when it comes to reading. For improved vision from an intermediate distance, tri-focal lenses are recommended as opposed to bifocals, which are more frequently used today in preference to spectacles.