Glasses – also called eyeglasses (formal), spectacles, or specs (informal) – are frames bearing lenses worn in front of the eyes, normally for vision correction or eye protection. Safety glasses are a kind of eye protection against flying debris or against visible and near visible light or radiation. Sunglasses allow better vision in bright daylight, and may protect against damage from high levels of ultraviolet light. Other types of glasses may be used for viewing visual information (such as stereoscopy) or simply just for aesthetic or fashion values.
Historical types of glasses include the pince-nez, monocle, lorgnette, and scissor or scissors-glasses.
Modern glasses are typically supported by pads on the bridge of the nose and by temple arms (sides) placed over the ears. CR-39 lenses are the most common plastic lenses due to their low weight, high scratch resistance, low dispersion, and low transparency to ultraviolet and infrared radiation. Polycarbonate and Trivex lenses are the lightest and most shatter-resistant, making them the best for impact protection.
An unpopular aspect of glasses is their inconvenience. Through modern frames can be both lightweight and flexible, and new lens materials and optical coatings are resistant to breakage or scratching, glasses can still cause problems during rigorous sports. Visibility can be significantly reduced by becoming greasy, trapping vapour when eating hot food, swimming, walking in rain or rapid temperature changes (such as walking into a warm building from cold temperatures outside). Scraping, fracturing, or breakage of the lenses require time-consuming and costly professional repair.Reading glasses
Magnifying lenses or generic spectacles that are used to treat mild presbyopia and hyperopia can be bought off the shelf. Although such glasses are generally considered safe, an individual prescription, as determined by an ophthalmologist or optometrist and made by a qualified optician, usually results in better visual correction and fewer headaches & visual discomfort. There have also been many cases where people have delayed having a proper eye examinaton with an optometrist or ophthalmologist, preferring to purchase off the shelf glasses, who have put their sight at risk from conditions such as AMD, Glaucoma and complications from Diabetes. It is important to stress off the shelf readers are not a replacement for regular eye examinations.
Typical pair of reading glasses.
Reading glasses come in two main styles: full frames, in which the entire lens is made in the reading prescription, and half-eyes, the smaller "Ben Franklin" style glasses that sit lower down on the nose.
Full reading glasses are more suitable for people who only need them for close-up reading while half-eye reading glasses can be used to read at smaller or larger distances. The reading glasses are most of the time needed by people who have never worn glasses.
Although specialists recommend individuals who need to wear eyeglasses to have them custom-made according to their own needs, most of the patients prefer buying them at a pharmacy or department store. This type of eyeglass-shopping became very popular in the 1990s when it was estimated that over 30 million pairs were sold per year. These reading glasses are not as expensive as the custom-made ones and they are certainly designed to catch the buyer's eye. Glasses that can be purchased off the shelf are available in a wide variety of colors and designs, suitable for different tastes. As this habit can result in worsening one's vision problems, there is a new alternative to buy eyeglasses easy and cheap from online prescription eyeglasses stores.
One downside of ready-made eyeglasses is that their prescription is the same for each eye. The optical center of each lens is also the same. Yet, most individuals who need reading glasses need different prescriptions in each eye. Wearing ready-made eyeglasses can result in headaches, eyestrain or nausea, and these "side effects" increase with the extent of the prescriptions' mismatch. Another disadvantage is that people with a strong prescription will not find ready-made solutions. They usually cannot be found with spherical corrections greater than plus or minus three dioptres, and of course are never corrected for astigmatism.
Some feel that it would be possible to obtain a cheap frame for their existing lenses by first purchasing ready-mades; while this may be possible for some, the problem with the idea is twofold; there is no standard for lens shapes, so without resorting to extreme fitting methods like glue, it it unlikely that the right fitting could be found; the ready-mades themselves might have their existing lenses glued in place, so could be difficult to remove.