Bifocal Lenses

When two prescriptions come in one lens, it is called a bifocal. The term bifocal means literally "Two Focuses". It is meant to describe eyeglass lenses that enable the user to see clearly at two different distance ranges through one lens. Benjamin Franklin is credited with inventing the first bifocal lens by gluing two lens halves from different prescriptions together. Bifocals are used for many reasons, but the main reason is Presbyopia, a condition that affects every adult above the age of 40 years. Presbyopia is when the human near focus system gradually becomes unable to focus on objects that are closer in. At that point, the prescription that helps people to see objects clearly at distance is no longer sufficient to see close objects also. Bifocals have an additional power on the bottom part of the lens to aid close focus in presbyopic people so they can see far and close with one lens. Some people who are young can see far away and close with one prescription, then as they age, it becomes necessary to have an addition in power in the bottom of the lens. Bifocals come in many shapes and styles:A blended bifocal may be any of the above lenses where the line is blended out, leaving a blurry area across where the old line was. A blended bifocal is not a multifocal or progressive lens . Flat Top Bifocals This is the most popular bifocal form and is available with the bifocal portion made in a variety of widths to help with various close-up occupations. Flat top bifocals are made in every type of lens material.Franklin Style (Executive) BifocalsSometimes used for those who need a wide field of vision for near work (accountants, for example), Franklin style bifocals have a distinctive appearance and are thicker because of their design. They are generally only available in glass, hard resin and photochromatic glass. They are being replaced by wide Flat Top bifocals.Trifocals Trifocals come in a variety of designs. Flat-top trifocals are the most widely used form. The added segment provides clear vision at arm's length distance, the area that is usually bluffed for bifocal wearers. Trifocals are available in all lens materials.Progressives (no line bifocals) These lenses provide all the benefits of bifocals but add the feature of continuous clear vision at all distances, including mid-range distance (arm's length). Progressives have the cosmetic advantage of appearing to be single vision lenses so they never reveal the user wears bifocals. Progressives are available in all lens materials and also made in aspheric form. Because of their many benefits, they are becoming the lens of choice for bifocal and trifocal wearers.