subject: Today It's Easy To Purchase Cheap Glasses For Optical Use [print this page] Glasses (also called eyeglasses or spectacles) are frames holding lenses worn in front of the eyes, commonly for sight rectification, or for protection from UV rays and foreign particles.
Contemporary glasses are typically supported by pads on the bridge of the nose and by temple arms placed over the ears. Historical types include the pince-nez, which are supported without earpieces, by pinching the bridge of the nose; monocle, which consists of a round lens, generally with a wire ring around the perimeter that can be attached to a string, used to correct the vision in only one eye; lorgnette, a pair of spectacles with a handle; and scissors-glasses, ordinarily used to correct distance-vision, mounted on scissoring stems.
There are several types of lens used in eyeglasses; the most commonly used are the single lens type, because young people and many adults do not need bifocals. Bifocals are required when a person's eyes are bad enough that they need help seeing close as well as far away. There are two types of bifocals, flat-top, which have visibly noticeable lines between the two different strengths of lenses and progressive, which do not have lines and are sometimes advertised as no-line bifocals.
Eyeglass lenses are usually produced from plastic, including CR-39 and polycarbonate. These materials reduce the danger of breaking and weigh less than glass lenses. Plastics have more beneficial optical properties than glass. These include better transmission of viewable light and broader absorption of Ultraviolet light. Some plastics have a greater power of deflection than most types of glass; this is functional in the making of corrective lenses shaped to correct assorted vision irregularities such as myopia, allowing sparser lenses.
Plastic lenses have a lot of options, such as photo chromatic, which enables the lenses to turn dark in bright light and return to clear when a person is dealing with dim light or wearing them at night. Polarized glasses protect people's eyes from ultra violet rays, which can damage the eyes. Sunglasses often use polarized lenses. Newer plastic lenses, called iZon, can likewise correct for the symptoms of the advanced order distortions that naturally happen on a persons optical system (including retina, lens, and cornea). These lenses produce clearer vision for people who have troubles with blurry or dim vision, as well as help shrink the halos, starbursts, and comet-tails frequently associated with nighttime driving.
These extra treatments are very nice to have but if you want really cheap glasses, then order plastic lenses with no extras; however, optometrists for ultimate eye protection always suggest ultra violet protection. Plastic is not always the right choice, however if you need very strong glasses, plastic is can only be produced to offer up to a certain strength.
When you purchase eyeglasses online to get cheap glasses, recording your eyeglasses prescription accurately when ordering your glasses is exceedingly essential! RX cards may vary across regions, but there are more often than not accepted criteria for the abbreviations and figures that you'll discover on your RX Card.
by: Lawrence White
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