Eyeglasses are frames containing lenses that are placed in front of eyes to correct vision or provide protection. Safety glasses offer protection against flying objects, light, or radiation. Sunglasses improve vision in bright light and can minimize ultraviolet light damage. Other glasses can help with the viewing of visual information or be worn for aesthetic reasons.
Glasses have padded supports that rest on the bridge of the nose and have sides that sit over the ears. The most common lenses that are used are CR-39 lenses. These are light, scratch resistant, have low dispersion, and block ultraviolet and infrared radiation.
There are many types of eyeglasses. These include corrective, safety, sun, 3D, reading, bifocal, trifocal, progressive, and extreme magnification glasses. Corrective glasses use lenses to modify the lenses focal length to improve nearsightedness, farsightedness, and astigmatism.
Nearsightedness is when far away objects look blurry but close objects are seen clearly. The lenses worn by these individuals are concave. Farsightedness is corrected with convex lenses to help make close up objects less blurry. Cylindrical lenses are used for astigmatism, which is a disorder that effects how light rays are passed to the retina. Corrective eyeglasses improve the sight of individuals with these problems and reduce any side effects they were experiencing, such as headaches.
Safety glasses are made of a plastic lens that is resistant to shattering. In this way they prevent damage to eyes from any flying debris. There is great variability in the level of protection provided by products. Ones worn in medical fields are designed to shield against blood splatter. Those worn in factories must protect against sawdust, metal, or flying wood. Factory glasses will have a stronger lens with further shielding than the medical ones. Lenses in either can be shaped so they are also corrective.
Sunglasses can be prescription or not and use lenses that are darkened. This darkening gives protection against light, including UV rays. Photochromatic lenses may be used as well, which darken only in the presence of UV light. Light polarization is also possible, which helps to eliminate glare. This would be especially beneficial for pilots, who might otherwise be blinded during flight.
The yellow shaded lens increases the contrast of colors and improves depth perception. These work well for seeing at dusk but inhibit vision at nighttime. Sometimes these are worn not to protect the eyes but merely for aesthetic reasons. Blind individuals may also wear opaque glasses to keep their eyes hidden from view.
3D glasses give the illusion of three dimension when looking at a two dimensional surface. This is done by having one red lens and one blue one. Or another option is to have one polarized vertically and the other polarized horizontally. The key is to have each eye take in different information.
Eyeglasses come in all shapes, sizes, and uses. They are worn for sight correction and vision protection, and sometimes only to make a fashion statement. Even 3D versions are available and used to see in three dimensions for the sake of entertainment.