There are three general types of computer glasses: single-vision lenses, flat-top bifocals, and variable-focus glasses. Each of these types helps improve an individual's eyesight, clarifying his vision of what is displayed on the computer monitor and maximizing the visible area. The lenses of these types of computer glasses can be further modified to suit the individual's preferences. Many computer glasses have lenses that are treated with special coatings that reduce glare from the computer screen, providing relief from eyestrain. Others have a special tint that correct colors for individuals with vision problems; these types of lenses are typically used by elderly users, as the ability to correctly see color tends to deteriorate with age.
Computer glasses with single-vision lenses allow individuals to better focus their eyesight on the computer screen. Wearing these glasses reduces the number of obstructions users see while working on the computer. One important drawback to single-vision lenses, however, is that they are calibrated in such a way that only objects just as distant from the user as the computer screen is will appear clear; items that are closer or farther than the monitor will appear blurry.
Flat-top bifocals, on the other hand, allow better vision at multiple ranges. The lenses are usually separated into two halves — the upper half is calibrated to clarify vision on objects at the computer screen's distance, while the lower half is designed to improve vision on closer materials. These computer glasses are ideal for individuals whose work requires them to work with items outside of the computer screen. Many individuals will find that working with flat-top bifocals can be difficult, however, as most designs have a thin line running across the middle of each lens to separate the two vision ranges.
Variable-focus computer glasses improve vision at three ranges, allowing for maximum versatility. Unlike flat-top bifocals, variable-focus glasses have no visible delineation between the different vision ranges, allowing for clear, unobstructed vision of the work at hand. The lenses are often difficult to craft, making them much more expensive than the other two options.
Computer glasses often have lenses that are coated with special materials that address issues such as glare and computer vision syndrome. Some glasses are tinted to reduce the white glare from computer screens, while others are coated with melanin to reduce overall glare and improve contrast, as well as block out potentially harmful ultraviolet (UV) rays. Computer glasses can also be specially made to correct discoloration in an individual's vision; rose-tinted and blue-tinted glasses, for example, can allow users to better differentiate certain colors from others.