Single Vision Lenses
This is the simplest type of lens option. Single vision lenses are used to correct a single vision problem. This can be nearsightedness, farsightedness, or astigmatism. Most of the time they are used to correct one’s distance vision, however, can also be prescribed for exclusive use for reading or computer work.
For those over 40, those with focusing or accommodative disorders, or children with rapidly progressing nearsightedness, prescription multifocals are often prescribed. These lenses correct for the unique problem of blurred vision associated with close work and reading. The essence of the lens is that in different regions of the lens, you will find a different lens power. A traditional bifocal lens has two distinct powers in it, separated by a line that is visible to the wearer and onlookers alike. This lens usually is meant to correct for faraway and close up vision. It does allow for crisp vision at each of these discrete distances. There is not however, any part of the lens allocated for intermediate-length tasks such as looking at a computer monitor.
A trifocal lens has the same appearance as a traditional bifocal, but there is a second line, or segment, designed to correct for a discrete intermediate-range distance.
A progressive multifocal lens (PAL) has many advantages over the other two. These allow for clear vision at any distance from the wearer, not just two or three. Furthermore, there is not the cosmetic distraction of a line through a portion of the lens, making it impossible for other individuals to see a bifocal in the glasses.
Most of us would not sit two feet from our television and stare at it for several hours, yet are expected to do just that at our jobs. Computer vision syndrome is very real and can be very debilitating. Therefore, we will commonly modify any of the above options to make computer use much less strenuous. The biggest advantage to dedicated computer glasses over standard multifocal lenses is the wider part of the lens is focused to your computer distance, rather than for faraway. An anti-glare coating is also highly recommended for computer users.