Almost all of us will develop presbyopia at some point in our lives because it’s the natural result of aging, usually starting around middle age and progressing at a constant rate after onset.
Presbyopia refers to a condition where the eye loses its ability to focus on objects close up. Most people begin to experience blurred vision when reading or doing other close up work around age 40. Presbyopia is usually caused by a stiffening of the eye tissue that prevents the eyes from focusing on objects close up.
If you are currently wearing prescription glasses, being diagnosed with presbyopia generally means that you will need to start wearing multifocal lenses so you can continue to see clearly at all distances.
Bifocal, trifocal and progressive glasses are all designed to improve vision for people with presbyopia. All three of these solve the problem of needing a different lens curvature for correcting distance viewing than they would for close-up reading. But there are differences between bifocal, trifocal and progressive lenses. Here’s how each one works to offset the effects of presbyopia.
How Bifocal, Trifocal and Progressive Lenses Work
While bifocal, trifocal and progressive lenses all work to increase your ability to focus clearly up close and at short range, as well as at a distance; each does it in different portions of the lens.
Bifocal lenses feature two separate lens powers separated by a distinct boundary and work by allowing you to use the top part of the lens for distance viewing and the bottom part of the lens for reading and short range vision.
Bifocal lenses are still popular but many prefer trifocal lenses, which are made similar to bifocals but with three separate lens powers instead of two. These lenses have three regions that correct for distance, intermediate (arm’s length), and near vision.
The additional segment for intermediate vision is placed above the reading section.
Progressive lenses are multi-focal lenses that provide different lens strengths without the dividing lines of traditional bifocals and trifocals. Vision runs the length of the lens to allow you to see clearly at a distance, at arm’s length and for reading or other close-up work.
Progressive lenses avoid the distinct separations of traditional bifocal and trifocal lenses by using a gradient curvature, which offers a more natural field of vision than bifocal or trifocal lenses. And that allows for a more natural, more flattering way of seeing.
Advantages of Bifocal and Trifocal Lenses
These days, most people who need vision correction for both far and near distances choose line-free progressive lenses but conventional bifocals and trifocals do have some advantages over progressives.
The main advantage of bifocal and trifocal lenses is that they usually provide a wider lens area for reading and computer work than progressive lenses do. There are also many special-purpose bifocal and trifocal lenses available that are designed especially for computer work and for other jobs that require exceptional near vision.