Editing Glasses (section)

=== Corrective ===
{{Main|Corrective lens|Refractive error}}
[[File:Refraction through glasses 090306.jpg|thumb|A [[skyline]] seen through a corrective lens, showing the effect of [[refraction]]]]
[[File:Microfiber cloth.jpg|thumb|[[Microfiber cloth]] designed for cleaning corrective lenses without scratching sensitive glass]]
Corrective lenses are used to correct [[refractive error]]s by bending the light entering the eye in order to alleviate the effects of conditions such as [[myopia|nearsightedness (myopia)]], [[hypermetropia|farsightedness (hypermetropia)]] or [[astigmatism]]. The ability of one's eyes to accommodate their focus to near and distant focus alters over time. A common condition in people over forty years old is [[presbyopia]], which is caused by the eye's [[lens (anatomy)|crystalline lens]] losing elasticity, progressively reducing the ability of the lens to [[accommodation (eye)|accommodate]] (i.e. to focus on objects close to the eye). Few people have a pair of eyes that show exactly equal refractive characteristics; one eye may need a "stronger" (i.e. more refracting) lens than the other.

Corrective lenses bring the image back into focus on the retina. They are made to conform to the [[Eyeglass prescription|prescription]] of an [[ophthalmologist]] or [[optometrist]]. A [[lensmeter]] can be used to verify the specifications of an existing pair of glasses. Corrective eyeglasses can significantly improve the [[life quality]] of the wearer. Not only do they enhance the wearer's visual experience, but can also reduce problems that result from eye strain, such as [[headaches]] or squinting.

The most common type of corrective lens is "single vision", which has a uniform [[refractive index]]. For people with [[presbyopia]] and [[hyperopia]], [[bifocals|bifocal]] and [[trifocal]] glasses provide two or three different refractive indices, respectively, and [[progressive lenses]] have a continuous gradient.<ref>{{Citation |title=Eyeglasses - All What You Need to Know |work=Eyewa Blog |url=https://eyewa.com/blog/eyeglasses/ |access-date=24 March 2020 |language=en-US}}</ref>  Lenses can also be manufactured with high refractive indices, which allow them to be more lightweight and thinner than their counterparts with "low" refractive indices.

[[Reading glasses]] provide a separate set of glasses for focusing on close by objects. Reading glasses are available without prescription from [[drugstore]]s, and offer a cheap, practical solution, though these have a pair of simple lenses of equal power, and so will not correct refraction problems like [[astigmatism]] or refractive or prismatic variations between the left and right eye. For the total correction of the individual's sight, glasses complying to a recent ophthalmic prescription are required.

People who need glasses to see often have corrective lens restrictions on their [[driver's licenses]] that require them to wear their glasses every time they drive or risk fines or jail time.

Some militaries issue prescription glasses to servicemen and women. These are typically [[GI glasses]]. Many state prisons in the United States issue glasses to inmates, often in the form of clear plastic aviators.

[[Adjustable-focus eyeglasses]] might be used to replace bifocals or trifocals, or might be used to produce cheaper single-vision glasses (since they do not have to be custom-manufactured for every person).
[[File:Hearing aid glasses.jpg|thumb|218x218px|1940s combined hearing aid glasses, on display at [[Thackray Museum of Medicine]].<ref>{{Cite web |title=128.030 {{!}} Collections Online |url=https://collections.thackraymuseum.co.uk/object-128-030 |access-date=2024-09-25 |website=collections.thackraymuseum.co.uk}}</ref>]]
[[Pinhole glasses]] are a type of corrective glasses that do not use a lens. Pinhole glasses do not actually refract the light or change focal length. Instead, they create a [[diffraction]] limited system, which has an increased depth of field, similar to using a small [[aperture]] in photography.  This form of correction has many limitations that prevent it from gaining popularity in everyday use. Pinhole glasses can be made in a [[DIY]] fashion by making small holes in a piece of card which is then held in front of the eyes with a strap or cardboard arms.

Glasses may also house other corrective or assistive devices. After the development of the [[transistor]] in the 1940s, combined eyeglass-hearing aids became popular. With thick-rimmed glasses the fashion at the time, a [[hearing aid]] could be concealed in the temple part of the frame. These fell out of fashion after the 1970s, but there are still occasions when combined eyeglass-hearing aids may be useful.<ref>{{Cite journal |last1=Uchanski |first1=Rosalie M. |last2=Sarli |first2=Cathy C. |title=20th Century Hearing Devices: Going, Going, Nearly Gone |url=http://dx.doi.org/10.1097/01.hj.0000616124.53833.22 |journal=The Hearing Journal |date=2019 |volume=72 |issue=12 |pages=10,12,13 |doi=10.1097/01.hj.0000616124.53833.22 |issn=0745-7472}}</ref>