Editing Glasses (section)

== Types ==
Glasses can be marked or found by their primary function, but also appear in combinations such as prescription sunglasses or safety glasses with enhanced magnification.

=== 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>

=== Safety ===
{{See also|Eye protection|Goggles}}
[[File:SafetyGlassesShield.jpg|thumb|[[Eye protection|Safety glasses]] with side shields]]

Safety glasses are worn to protect the eyes in various situations. They are made with break-proof plastic lenses to protect the eye from flying debris or other matter.<ref>{{Cite web |title=Personal Protective Equipment Eye and Face Protection (Appendix A) – Environmental Health and Safety |url=https://ehs.ncsu.edu/personal-protective-equipment-ppe/eye-and-face-protection-appendix-a/ |access-date=2024-07-03 |language=en-US}}</ref> Construction workers, factory workers, machinists and lab technicians are often required to wear safety glasses to shield the eyes from flying debris or hazardous splatters such as blood or chemicals.<ref>{{Cite web |title=Why do I need safety glasses? |url=https://www.mayoclinichealthsystem.org/hometown-health/speaking-of-health/why-do-i-need-safety-glasses |access-date=2024-07-03 |website=Mayo Clinic Health System |language=en}}</ref> As of 2017, dentists and surgeons in Canada and other countries are required to wear safety glasses to protect against infection from patients' blood or other body fluids. There are also safety glasses for [[welding]], which are styled like wraparound sunglasses, but with much darker lenses, for use in welding where a full-sized [[welding helmet]] is inconvenient or uncomfortable. These are often called "flash goggles" because they provide protection from welding flash.<ref>{{Cite web |last=Milani |first=Clara |date=2024-02-14 |title=What Glasses Prevent Welding Flash? Phillips Safety Has the Answer |url=https://phillips-safety.com/welding-safety/what-glasses-prevent-welding-flash-phillips-safety-has-the-answer/ |access-date=2024-07-03 |website=Phillips Safety {{!}} Leading Manufacturer of Occupational Safety Products |language=en-US}}</ref> [[Nylon]] frames are usually used for protective eyewear for sports because of their lightweight and flexible properties. Unlike most regular glasses, safety glasses often include protection beside the eyes as well as in front of the eyes.

=== Sunglasses ===
{{Main|Sunglasses}}
[[File:Woman wearing sunglasses.jpg|thumb|Woman wearing [[sunglasses]]]]

Sunglasses provide more comfort and protection against bright [[visible light|light]] and often against [[ultraviolet]] (UV) light. To properly protect the eyes from the dangers of UV light, sunglasses should have UV-400 blocker to provide good coverage against the entire light spectrum that poses a danger.<ref>{{Citation |title=Sunglasses not just an accessory in the Sunshine State |url=http://www.sun-sentinel.com/brandpublishing/sfl-sunglasses-not-just-an-accessory-in-the-sunshine-state-20180312-story.html |work=Sun-Sentinel.com |date=12 March 2018 |language=en-US |access-date=10 April 2018}}</ref>

Light [[Polarization (waves)|polarization]] is an added feature that can be applied to sunglass lenses. Polarization filters are positioned to remove horizontally polarized rays of light, which eliminates glare from horizontal surfaces (allowing wearers to see into water when reflected light would otherwise overwhelm the scene). Polarized sunglasses may present some difficulties for pilots since reflections from water and other structures often used to gauge altitude may be removed.  [[Liquid-crystal display]]s emit polarized light, making them sometimes difficult to view with polarized sunglasses. Sunglasses may be worn for aesthetic purposes, or simply to hide the eyes. Examples of sunglasses that were popular for these reasons include tea shades and [[Mirrorshades (fashion)|mirrorshades]]. Many [[blindness|blind]] people wear nearly opaque glasses to hide their eyes for cosmetic reasons. Many people with light sensitivity conditions wear sunglasses or other tinted glasses to make the light more tolerable.

Sunglasses may also have corrective lenses, which requires a prescription. Clip-on sunglasses or sunglass clips can be attached to another pair of glasses. Some wrap-around sunglasses are large enough to be worn over another pair of glasses. Otherwise, many people opt to wear [[contact lens]]es to correct their vision so that standard sunglasses can be used.

=== Mixed double-frame (Flip glasses) ===
[[File:Doubleframe uplifting eyewear - Nella.gif|thumb|left|Double-frame eyewear with one set of lenses on the moving frame and another pair of lenses on a fixed frame (optional).]]
The double frame uplifting glasses have one moving frame with one pair of lenses and the basic fixed frame with another pair of lenses (optional), that are connected by [[four-bar linkage]]. For example, sun lenses could be easily lifted up and down while mixed with [[myopia]] lenses that always stay on. [[Presbyopia]] lenses could be also combined and easily removed from the field of view if needed without taking off glasses. These glasses are often used for drivers going through tunnels, with the upper frame serving as sunglasses and the second frame as transparent lenses.

=== 3D glasses ===
{{Main|Stereoscopy#3D viewers|l1=3D Viewers}}
The [[stereoscopy|illusion of three dimensions]] on a two-dimensional surface can be created by providing each eye with different visual information. 3D glasses create the illusion of three dimensions by filtering a signal containing information for both eyes.  The signal, often light reflected off a movie screen or emitted from an electronic display, is filtered so that each eye receives a slightly different image. The filters only work for the type of signal they were designed for.

[[Anaglyph 3D]] glasses have a different colored filter for each eye, typically red and blue or red and green. A [[polarized 3D system]] on the other hand uses [[polarization (waves)|polarized]] filters. Polarized 3D glasses allow for color 3D, while the red-blue lenses produce an image with distorted coloration. An [[active shutter 3D system]] uses electronic [[Shutter (photography)|shutter]]s. [[Head-mounted display]]s can filter the signal electronically and then transmit light directly into the viewer's eyes.

Anaglyph and polarized glasses are distributed to audiences at [[3D film|3D movies]].  Polarized and active shutter glasses are used with many home theaters.  Head-mounted displays are used by a single person, but the input signal can be shared between multiple units.

=== Magnification (bioptics) ===
Glasses can also provide magnification that is useful for people with vision impairments or specific occupational demands.  An example would be ''[[Bioptics (device)|bioptics]]'' or ''bioptic telescopes'' which have small [[telescope]]s mounted on, in, or behind their regular lenses. Newer designs use smaller lightweight telescopes, which can be embedded into the corrective glass and improve aesthetic appearance (mini telescopic spectacles). They may take the form of self-contained glasses that resemble [[goggles]] or [[binoculars]], or may be attached to existing glasses.
[[File:Recumbent spectacles.jpg|thumb|McKie Reid recumbent glasses, on display at [[Thackray Museum of Medicine]].<ref>{{Cite web |title=128.080 {{!}} Collections Online |url=https://collections.thackraymuseum.co.uk/object-128-080 |access-date=2024-09-25 |website=collections.thackraymuseum.co.uk}}</ref>]]

=== Recumbent glasses ===
Recumbent or [[Prism (optics)|prism]] glasses are glasses that use a prism with a 90° [[refraction]] to allow the wearer to read or view a screen while lying on their back. Developed by [[Liverpudlian]] ophthalmologist Andrew McKie Reid in the 1930s to assist people bedbound by chronic illness or spinal injury, recumbent glasses have more recently been marketed not simply as an assistive device but also as 'lazy glasses'.<ref>{{Cite web |date=25 September 2024 |title=Glasses: Technology or Accessory? You Choose! |url=https://thackraymuseum.co.uk/glasses-technology-or-accessory-you-choose/ |website=Thackray Museum of Medicine}}</ref> They do not assist with vision, although they can be worn over regular corrective glasses.

=== Yellow-tinted computer/gaming glasses ===
Yellow-tinted glasses are a type of glasses with a minor yellow tint. They perform a slight color correction, on top of reducing eyestrain from lack of blinking. They may also be considered minor corrective non-prescription glasses.<ref>{{Citation |last=Loria |first=Kevin |title=Computer glasses that claim to protect your eyes from screens are selling like crazy, but they probably aren't doing you much good |date=21 February 2017 |url=https://www.businessinsider.com/blue-blocking-glasses-science-screens-not-destroying-vision-2017-2 |work=Business Insider}}</ref> Depending on the company, these computer or gaming glasses can also filter out [[#blue-light|high energy blue and ultra-violet light from LCD screens]], [[fluorescent lighting]], and other sources of light. This allows for reduced eye-strain.<ref>{{Citation |last=Heiting |first=Gary |title=Computer Eye Strain: 10 Steps For Relief |url=http://www.allaboutvision.com/cvs/irritated.htm |work=All about vision.com |access-date=1 September 2017}}</ref> These glasses can be ordered as standard or prescription lenses that fit into standard optical frames.<ref>{{Citation |title=BluTech Lenses – Technology, The story behind BluTech Lenses |url=http://blutechlenses.com/technology/ |work=BluTech Lenses |access-date=11 May 2015 |archive-date=4 May 2015 |archive-url=https://web.archive.org/web/20150504104341/http://blutechlenses.com/technology/ |url-status=dead }}</ref>

{{anchor|blue-light}}

=== Blue-light blocking glasses ===
{{Main|Biological effects of high-energy visible light}}
By the end of the 2010s, eyeglasses that filter out [[Light spectrum|blue light]] from [[computers]], [[smartphones]] and [[Tablet computer|tablets]] are becoming increasingly popular in response to concerns about problems caused by blue light overexposure.<ref name="AAO-Computer-Glasses">{{Citation |last=Vimont |first=Celia |title=Are Computer Glasses Worth It? |date=27 April 2017 |url=https://www.aao.org/eye-health/tips-prevention/are-computer-glasses-worth-it |archive-url=https://web.archive.org/web/20200923163359/https://www.aao.org/eye-health/tips-prevention/are-computer-glasses-worth-it |others=Reviewed by Rahul Khurana, MD |publisher=[[American Academy of Ophthalmology]] |archive-date=23 September 2020 |url-status=live}}</ref><ref name=WebMD-Blue-Light-Glasses />
The problems claimed range from [[dry eyes]] to [[eye strain]], [[sleep cycle]] disruption, up to [[macular degeneration]] which can cause partial blindness.<ref name=AAO-Computer-Glasses /> They may also block out [[ultraviolet]] (UV) radiation. However, there is no measurable UV light from computer monitors.<ref name=AAO-Computer-Glasses /><ref>{{Citation |last1=Duarte |first1=IA |title=Ultraviolet radiation emitted by lamps, TVs, tablets and computers: are there risks for the population? |date=2015 |work=An Bras Dermatol |volume=90 |issue=4 |pages=595–7 |doi=10.1590/abd1806-4841.20153616 |pmc=4560556 |pmid=26375236 |last2=Mde F |first2=Hafner |last3=Malvestiti |first3=AA}}</ref>{{Contradictory inline|Glasses#Types}} The problem of [[computer vision syndrome]] (CVS) can result from focusing the eyes on a screen for long, continuous periods. Many times the glasses do not appear to have much of a tint, or, if any, a slight yellow tint, but they may be more heavily tinted.

Long hours of computer use (not blue light) may cause eye strain.<ref name="AAO-Computer-Glasses" /><ref name="AAO-Blue-Light">{{Citation |last=Porter |first=Daniel |title=Blue Light and Digital Eye Strain |date=16 January 2020 |url=https://www.aao.org/eye-health/tips-prevention/blue-light-digital-eye-strain |archive-url=https://web.archive.org/web/20201028103424/https://www.aao.org/eye-health/tips-prevention/blue-light-digital-eye-strain |others=Reviewed by Ninel Z Gregori, MD |publisher=[[American Academy of Ophthalmology]] |archive-date=28 October 2020 |url-status=live}}</ref><ref name="WebMD-Blue-Light-Glasses" /><ref>{{Citation |last=Iallonardo |first=Marisa |title=Do blue light glasses work ? |date=24 May 2020 |url=https://www.insider.com/do-blue-light-glasses-work |others=Reviewed by Benjamin Bert, MD |publisher=Business Insider}}</ref>
Many eye symptoms caused by computer use will lessen after the usage of the computer is stopped.<ref name="AAO-Computer-Glasses" />
Decreasing evening screen time and setting devices to night mode will improve sleep.<ref name="AAO-Blue-Light" /><ref>{{Citation |last=Hazanchuk |first=Vered |title=Should You Use Night Mode to Reduce Blue Light? |date=7 May 2019 |url=https://www.aao.org/eye-health/tips-prevention/should-you-use-night-mode-to-reduce-blue-light |archive-url=https://web.archive.org/web/20200908081841/https://www.aao.org/eye-health/tips-prevention/should-you-use-night-mode-to-reduce-blue-light |others=Reviewed by Raj K Maturi, MD |publisher=[[American Academy of Ophthalmology]] |archive-date=8 September 2020 |url-status=live}}</ref>
Several studies have shown that blue light from computers does not lead to eye diseases, including macular degeneration.<ref name="AAO-Blue-Light" /><ref>{{Citation |last=Porter |first=Daniel |title=Digital Devices and Your Eyes |date=15 November 2019 |url=https://www.aao.org/eye-health/tips-prevention/digital-devices-your-eyes |archive-url=https://web.archive.org/web/20200809234027/https://www.aao.org/eye-health/tips-prevention/digital-devices-your-eyes |others=Reviewed by Ninel Z Gregori, MD |publisher=[[American Academy of Ophthalmology]] |archive-date=9 August 2020 |url-status=live}}</ref><ref>{{Citation |last=Caporuscio |first=Jessica |title=Can blue light glasses prevent damage to eyes? |date=2 June 2020 |url=https://www.medicalnewstoday.com/articles/do-blue-light-glasses-work |work=[[Healthline|MedicalNewsToday]] |archive-url=https://web.archive.org/web/20201016101735/https://www.medicalnewstoday.com/articles/do-blue-light-glasses-work |others=Medically reviewed by Ann Marie Griff, O.D |archive-date=16 October 2020}}</ref> The total amount of light entering the eyes can be adjusted without glasses using the screen brightness settings. Similarly, the blue light can often specifically be adjusted using the "night mode" of different operating systems, which can usually be activated outside of nighttime hours.

{{anchor|VDU}}The [[American Academy of Ophthalmology]] (AAO) does not recommend special eyewear for computer use,<ref name=AAO-Computer-Glasses /><ref name="WebMD-Blue-Light-Glasses">{{Citation |title=Blue Light Glasses - Helpful or Just Hype? |date=16 December 2019 |url=https://www.webmd.com/eye-health/news/20191216/do-blue-light-glasses-work |work=WebMD Health News |archive-url=https://web.archive.org/web/20200807023240/https://www.webmd.com/eye-health/news/20191216/do-blue-light-glasses-work |archive-date=7 August 2020}}</ref>
although it recommends using [[prescription glasses]] measured specifically for computer screen distance (depending on individuals, but possibly 20–26 inches from the face), which are not the same as "blue-light blocking" glasses.<ref>{{Citation |last=Boyd |first=Kierstan |title=Computers, Digital Devices and Eye Strain |date=3 March 2020 |url=https://www.aao.org/eye-health/tips-prevention/computer-usage |archive-url=https://web.archive.org/web/20201003115848/https://www.aao.org/eye-health/tips-prevention/computer-usage |others=Reviewed by James M Huffman, MD |publisher=[[American Academy of Ophthalmology]] |archive-date=3 October 2020 |url-status=live}}</ref>
The position of the [[College of Optometrists]] (UK) is that "the best scientific evidence currently available does not support the use of blue-blocking spectacle lenses in the general population to improve visual performance, alleviate the symptoms of eye fatigue or visual discomfort, improve sleep quality or conserve macula health."<ref>{{Citation |title=Blue blocking spectacle lenses - The College's position on blue blocking spectacle lenses |url=https://www.college-optometrists.org/the-college/policy/position-statements/blue-blocking-spectacle-lenses.html |archive-url=https://web.archive.org/web/20200919122059/https://www.college-optometrists.org/the-college/policy/position-statements/blue-blocking-spectacle-lenses.html |access-date=24 October 2020 |archive-date=19 September 2020 |url-status=live}}</ref>