Editing Corrective lens (section)

== Lens materials ==
{{More citations needed section|date=January 2015}}

=== Optical crown glass ===
* [[Refractive index]] ({{mvar|n}}{{sub|d}}): 1.52288
* [[Abbe number]] ({{mvar|V}}{{sub|d}}): [https://www.knightoptical.com/_public/documents/1372681801_sheetglassb270tsgb270.pdf 58.5]{{Dead link|date=September 2023 |bot=InternetArchiveBot |fix-attempted=yes }}
* [[Density]]: 2.56 g/cm³ (the heaviest corrective lens material in common use, today)
* [[Cutoff (physics)|UV cutoff]]: [https://www.knightoptical.com/_public/documents/1372681801_sheetglassb270tsgb270.pdf 320 nm]{{Dead link|date=September 2023 |bot=InternetArchiveBot |fix-attempted=yes }}

Glass lenses have become less common owing to the danger of shattering and their relatively high weight compared to [[CR-39]] plastic lenses. They still remain in use for specialised circumstances, for example in extremely high prescriptions (currently, glass lenses can be manufactured up to a [[refractive index]] of 1.9) and in certain occupations where the hard surface of glass offers more protection from sparks or shards of material. If the highest Abbe number is desired, the only choices for common lens optical material are optical crown glass and CR-39.

Higher-quality optical-grade glass materials exist (e.g. [[Borosilicate glass|Borosilicate crown glasses]] such as [http://www.pgo-online.com/intl/katalog/BK7.html BK7] {{nobr|( {{mvar|n}}{{sub|d}} {{=}} 1.51680 ,}} {{nobr| {{mvar|V}}{{sub|d}} {{=}} 64.17 ,}} {{nobr| {{mvar|D}} {{=}} 2.51 g/cm³ ),}} which is commonly used in telescopes and binoculars, and [[fluorite]] [[crown glass (optics)|crown glasses]] such as the best optical quality low dispersion glass currently in production, [https://www.schott.com/advanced_optics/us/abbe_datasheets/schott-datasheet-n-fk58.pdf N-FK58] made by the German company Schott with the following characteristics {{nobr|( {{mvar|n}}{{sub|d}} {{=}} 1.456 ,}} {{nobr| {{mvar|V}}{{sub|d}} {{=}} 90.90 ,}} {{nobr| {{mvar|D}} {{=}} 3.65 g/cm³ )}} and are commonly used in high-end camera lenses).

One must bear in mind that the human eye itself has an [https://application.wiley-vch.de/books/sample/3527410686_c02.pdf Abbe number {{nobr| {{mvar|V}}{{sub|d}} ≈ 50.2 }} ] so the expensive, high-end optical glass types mentioned above have little value for central vision; however, the wearer's view through the side of a glass lens is not comparable to central vision through the eye: Low dispersion glass definitely makes optically superior corrective lenses since it greatly reduces color-fringing of edge-wise viewed contrasty objects, compared to all available plastics. But glass lenses are much heavier, and making them requires specialized glass grinding equipment no longer common in ordinary prescription lens labs: At present, one is often hard-pressed to find an optical laboratory that has the machinery needed shape custom glass lenses.

A further complication for seeking lenses made of better, even-lower dispersion glass, is that the specialty glass is often expensive. Also, many exotic glass types, with [[Abbe number]] {{nobr|{{mvar|V}}{{sub|d}} {{math|≳}} 65 ,}} contain oxides of heavy metals such as [[arsenic]] or [[lanthanum]], some of which are toxic. The need for special venting to protect technicians from exposure to powdered toxic glass further limits the number of optical labs that can safely grind super-low dispersion / large Abbe number glass.

Abbe numbers ({{mvar|V}}{{sub|d}}) in excess of Crown Glass and CR-39 are mainly warranted only for unusual special uses, such as
* extreme positive or negative [[diopter]] prescriptions
* very large size lenses, such as might cover a good portion of the face
* low wearer tolerance of color fringing
* occupations that involve work with very high contrast elements (e.g. reading dark print on white paper under bright light)
* construction work that requires viewing contrasting dark building elements against a cloudy white sky
* workplace with bright recessed can lighting or other darkened room lighting, concentrated on a small areas, shining on bright reflective surfaces (e.g. display counters at jeweler stores).

=== Optical plastics ===
Plastic lenses are currently the most commonly prescribed lens, owing to their relative safety, low cost, ease of production, and high optical quality. The main drawbacks of many types of plastic lenses are the ease by which a lens can be scratched, and the limitations and costs of producing higher-index lenses.

==== CR-39 ====
{{main|CR-39}}
* [[Refractive index]] ({{mvar|n}}{{sub|d}}): 1.498 (standard)
* [[Abbe number]] ({{mvar|V}}{{sub|d}}): 59.3
* [[Density]]: 1.31 g/cm³
* [[Cutoff (physics)|UV cutoff]]: 355&nbsp;nm

[[CR-39]] lenses are inherently scratch resistant.

==== Trivex ====
* [[Refractive index]] ({{mvar|n}}{{sub|d}}): 1.532
* [[Abbe number]] ({{mvar|V}}{{sub|d}}): 43–45 (depending on licensing manufacturer)
* [[Density]]: 1.1 g/cm³ (the lightest corrective lens material in common use)
* [[Cutoff (physics)|UV cutoff]]: 394&nbsp;nm

Trivex was invented by Edwin C. Slagel and patented in September 1998.<ref name="patent">
{{cite patent
 | country = US
 | number  = 6127505
 | status  = Expired
 | title   = Impact resistant polyurethane, and meteor of manufacture thereof
 | pubdate = 3 October 2000
 | gdate   = 3 October 2000
 | fdate   = 2 September 1998
 | pridate = 2 February 1995
 | inventor= Slagel, Edwin C.
 | assign1 = Simula, Inc.
 | url     = https://patentimages.storage.googleapis.com/da/bd/da/1ce12187652eef/US6127505.pdf
}}
</ref>

Trivex was developed in 2001 by [[PPG Industries]] for the military as transparent armor.<ref name=eyecarebusiness-2001>{{cite news |last=Bruneni |first=Joseph L. |date=1 September 2001 |title=Alternative lens material |website = Eyecare Business |url=http://www.eyecarebusiness.com/articleviewer.aspx?articleID=50369 }}</ref> With [[Hoya Corporation]] and Younger Optics, PPG announced the availability of Trivex for the optical industry in 2001.<ref name=eyecarebusiness-2001/> Trivex is a urethane-based pre-polymer.<ref name=patent/> PPG named the material Trivex because of its three main performance properties: Superior optics, ultra lightweight, and extreme strength.<ref name=eyecarebusiness-2001/>

Trivex is a relative newcomer that possesses the UV-blocking properties and shatter resistance of [[polycarbonate]] while at the same time offering far superior optical quality (i.e., higher Abbe number) and a slightly lower density. Its lower refractive index of {{nobr| {{mvar|n}}{{sub|d}} {{=}} 1.532 }} vs. polycarbonate's 1.586 may result in slightly thicker lenses depending upon the prescription. Along with polycarbonate and the various high-index plastics, Trivex is a lab favorite for use in rimless frames, owing to the ease with which it can be drilled and its resistance to cracking around the drill holes. One other advantage that Trivex has over polycarbonate is that it can be tinted.{{Citation needed|date = January 2015}}

==== Polycarbonate ====
* [[Refractive index]] ({{mvar|n}}{{sub|d}}): 1.586
* [[Abbe number]] ({{mvar|V}}{{sub|d}}): 30
* [[Density]]: 1.2 g/cm³
* [[Cutoff (physics)|UV cutoff]]: 385&nbsp;nm

Polycarbonate is lighter weight than normal plastic. It blocks UV rays, is shatter resistant, and is used in sports glasses and glasses for children and teenagers. Because polycarbonate is soft and will scratch easily, a scratch-resistant coating is typically applied after shaping and polishing the lens. Standard polycarbonate with an Abbe number of 30 is one of the worst materials optically if chromatic aberration intolerance is of concern. Along with Trivex and the high-index plastics, polycarbonate is an excellent choice for rimless eyeglasses. Similar to the high-index plastics, polycarbonate has a very low Abbe number, which may be bothersome to individuals sensitive to chromatic aberrations.

==== High-index plastics (thiourethanes) ====
* [[Refractive index]] ({{mvar|n}}{{sub|d}}): 1.600–1.740
* [[Abbe number]] ({{mvar|V}}{{sub|d}}): 42–32 (higher indexes generally result in lower Abbe numbers)
* [[Density]]: 1.3–1.5 (g/cm³)
* [[Cutoff (physics)|UV cutoff]]: 380–400&nbsp;nm

High-index plastics allow for thinner lenses. The lenses may not be lighter, however, due to the increase in density vs. mid- and normal index materials. A disadvantage is that high-index plastic lenses have a much higher level of [[chromatic aberration]]s, which can be seen from their lower [[Abbe number]]s. Aside from the thinness of the lens, another advantage of high-index plastics is their strength and shatter resistance, although not as shatter resistant as [[polycarbonate]]. This makes them particularly suitable for rimless eyeglasses.

These high-refractive-index plastics are typically thiourethanes, with the [[sulfur]] atoms in the polymer being responsible for the high refractive index.<ref name="mitsui-high-n"/> The sulfur content can be up to 60 percent by weight for a material with index {{nobr|{{mvar|n}}{{sub|d}} {{=}} 1.74 .}}<ref name="mitsui-high-n">[http://www.mitsuichem.com/special/mr/resources/img/MR_article_in_MAFO_magazine_2009.pdf Is the sky the limit?] MAFO Ophthalmic labs & Industry, April 2009</ref>

=== Ophthalmic material property tables ===
:{| class="wikitable sortable" style="text-align:center;"
|+ Glass
|-
!scope="col" rowspan="2"| Material<br/>
!scope="col" rowspan="1"| Refrac-<br/>tive<br/>index
!scope="col" rowspan="1"| Abbe<br/>number
!scope="col" rowspan="1"| Specific<br/>gravity
!scope="col" rowspan="2"| UVB<br/>
!scope="col" rowspan="2"| UVA<br/>
!scope="col" rowspan="2"| Reflected<br/>light<br/>{{efn|group=glass|name="Reflected Light"}}
!scope="col" rowspan="1"| Minimum<br/>thickness<br/>{{nobr|typ / min}} 
!scope="col" rowspan="2"| Notes
|-
| {{small| ({{mvar|n}}{{sub|d}}) }}
| {{small| ({{mvar|V}}{{sub|d}}) }}
| {{small| (g/cm³) }}
| {{small| (mm) }}
|-
|style="text-align:left;"| 1.6 Glass
| 1.604
| 40
| 2.62&nbsp;g/cm³
| 100%
| 61%
| 10.68%
|
|style="text-align:left;"| VisionEase, X-Cel
|-
|style="text-align:left;"| 1.7 Glass
| 1.706
| 30
| 2.93&nbsp;g/cm³
| 100%
| 76%
| 13.47%
|
|style="text-align:left;"| X-Cel, VisionEase, Phillips
|-
|style="text-align:left;"| 1.8 Glass
| 1.800
| 25
| 3.37&nbsp;g/cm³
| 100%
| 81%
| 16.47%
|
|style="text-align:left;"| X-Cell, Phillips, VisionEase, Zhong Chuan Optical (China)
|-
|style="text-align:left;"| 1.9 Glass
| 1.893
| 31
| 4.02&nbsp;g/cm³
| 100%
| 76%
| 18.85%
|
|style="text-align:left;"| Zeiss, Zhong Chuan Optical (China)
|-
|style="text-align: left;"| Crown Glass
| 1.525
| 59
| 2.54&nbsp;g/cm³
| 79%
| 20%
| 8.59%
|
|style="text-align:left;"|
|-
|style="text-align:left;"| {{nobr|PhotoGray Extra}}
| 1.523
| 57
| 2.41&nbsp;g/cm³
| 100%
| 97%
| 8.59%
|
|style="text-align:left;"|
|}
{{notelist|group=glass|refs=
{{efn|group=glass|name="Reflected Light"|Reflected light calculated using [[Fresnel equations|Fresnel reflection equation]] for normal waves against air on two interfaces. This is a reflection without an AR coating.}}
}}

:{| class="wikitable sortable" style="text-align:center;"
|+ {{big|Optical plastics}}
|-
!scope="col" rowspan="2"| Material<br/>
!scope="col" rowspan="1"| Refrac-<br/>tive<br/>index
!scope="col" rowspan="1"| Abbe<br/>number<br/>
!scope="col" rowspan="1"| Specific<br/>gravity
!scope="col" rowspan="2"| UVB<br/>
!scope="col" rowspan="2"| UVA<br/>
!scope="col" rowspan="2"| [[Heat Distortion Temperature|HDT]]<br/>
!scope="col" rowspan="2"| Reflected<br/>light<br/>{{efn|group=plastic|name="Reflected Light"}}
!scope="col" rowspan="1"| Minimum <br/>thickness<br/>
!scope="col" rowspan="2"| Notes<br/>
|-
| {{small| ({{mvar|n}}{{sub|d}}) }}
| {{small| ({{mvar|V}}{{sub|d}}) }}
| {{small| (g/cm³) }}
| {{small| (mm) }}
|-
|style="text-align:left;"| CR-39 Hard Resin
| 1.49
| 59
| 1.31&nbsp;g/cm³
| 100%
| 90%
|
| 7.97%
| 2.0&nbsp;mm
|style="text-align:left;"|
|-
|NK-55
|1.56
|38
|1.28&nbsp;g/cm³
|
|
|
|
|
|
|-
|style="text-align:left;"| Essilor Ormix 1.6<ref>{{cite web |url=https://www.essilorpro.co.uk/Lenses/materials/Pages/Ormix.aspx |title=Ormix 1.6 |website=www.essilorpro.co.uk |access-date=14 March 2022 |archive-url=https://web.archive.org/web/20170225122146/https://www.essilorpro.co.uk/Lenses/materials/Pages/Ormix.aspx |archive-date=25 February 2017 |url-status=dead}}</ref>
| 1.6
| 41
| 1.30&nbsp;g/cm³
| 100%
| 100%
|
| {{#expr:((1-1.6)/(1+1.6))^2*2*100 round 2}}%
|
|style="text-align:left;"|
|-
|style="text-align:left;"| Hoya EYRY
| 1.70
| 36
| 1.41&nbsp;g/cm³
| 100%
| 100%
|
| 13.44%
| 1.5&nbsp;mm
|style="text-align:left;"|
|-
|style="text-align:left;"| MR-6 1.6 Plastic
| 1.6
| 36
| 1.34&nbsp;g/cm³
| 100%
| 100%
|
| 10.57%
|
|style="text-align:left;"|
|-
|style="text-align:left;"| MR-7 1.665 Plastic
| 1.665
| 32
| 1.35&nbsp;g/cm³
| 100%
| 100%
|
| {{#expr:((1-1.665)/(1+1.665))^2*2*100 round 2}}%
| 1.2&nbsp;mm
|style="text-align:left;"| Daemyung Optical (Ramia)
|-
|style="text-align: left;"| MR-7 1.67 Plastic<ref name="mitsuichem.com">{{cite web |url=http://www.mitsuichem.com/en/special/mr/products/index.htm |title=MR™ Series &#124; Products Line up |website=www.mitsuichem.com |access-date=14 March 2022 |archive-url=https://web.archive.org/web/20171006100414/http://www.mitsuichem.com/en/special/mr/products/index.htm |archive-date=6 October 2017 |url-status=dead}}</ref>
| 1.67
| 32
| 1.35&nbsp;g/cm³
| 100%
| 100%
| 85&nbsp;°C
| 12.26%
|
|style="text-align:left;"|
|-
|style="text-align:left;"| MR-8 1.6 Plastic<ref name="mitsuichem.com"/>
| 1.6
| 41
| 1.30&nbsp;g/cm³
| 100%
| 100%
| 118&nbsp;°C
| 10.43%
|
|style="text-align:left;"|
|-
|style="text-align:left;"| MR-10 1.67 Plastic<ref name="mitsuichem.com"/> 
| 1.67
| 32
| 1.37&nbsp;g/cm³
| 100%
| 100%
| 100&nbsp;°C
| 12.34%
|
|style="text-align:left;"|
|-
|style="text-align:left;"| MR-20 1.6 Plastic
| 1.60
| 42
| 1.30&nbsp;g/cm³
| 100%
| 100%
|
| {{#expr:((1-1.6)/(1+1.6))^2*2*100 round 2}}%
|
|style="text-align:left;"|
|-
|style="text-align:left;"| {{nobr|MR-174 1.74 Plastic<ref name="mitsuichem.com"/>}}
| 1.74
| 33
| 1.47&nbsp;g/cm³
| 100%
| 100%
| 78&nbsp;°C
| 14.36%
|
|style="text-align:left;"| Hyperindex 174 (Optima)
|-
|style="text-align:left;"| Nikon 4 Plastic NL4
| 1.67
| 32
| 1.35&nbsp;g/cm³
| 100%
| 100%
|
| {{#expr:((1-1.67)/(1+1.67))^2*2*100 round 2}}%
|
|style="text-align:left;"|
|-
|style="text-align:left;"| Nikon 5 Plastic NL5
| 1.74
| 33
| 1.46&nbsp;g/cm³
| 100%
| 100%
|
| {{#expr:((1-1.74)/(1+1.74))^2*2*100 round 2}}%
|
|style="text-align:left;"|
|-
|style="text-align:left;"| Polycarbonate
| 1.586
| 30
| 1.20&nbsp;g/cm³
| 100%
| 100%
|
| 10.27%
| 1.0&nbsp;mm
|style="text-align:left;"| Tegra (Vision-Ease) Airwear (Essilor)
|-
|style="text-align:left;"| PPG Trivex (average)
| 1.53
| 44
| 1.11&nbsp;g/cm³
| 100%
| 100%
|
| 8.70%
| 1.0&nbsp;mm
|style="text-align:left;"| PPG, Augen, HOYA, Thai Optical, X-cel, Younger
|-
|style="text-align:left;"| SOLA Finalite
| 1.60
| 42
| 1.22&nbsp;g/cm³
| 100%
| 100%
|
| 10.65%
|
|style="text-align:left;"|
|-
|style="text-align:left;"| SOLA Spectralite
| 1.54
| 47
| 1.21&nbsp;g/cm³
| 100%
| 98%
|
| 8.96%
|
|style="text-align:left;"| (also Vision 3456 (Kodak)?)
|-
|style="text-align:left;"| Tokai
| 1.76
| 30
| 1.49&nbsp;g/cm³
| 100%
| 100%
|
| {{#expr:((1-1.76)/(1+1.76))^2*2*100 round 2}}%
|
|style="text-align:left;"|
|}
{{notelist|group=plastic|refs=
{{efn|group=plastic|name="Reflected Light"|Reflected light calculated from {{mvar|N}}{{sub|d}} using [[Fresnel equations|Fresnel reflection equation]] for normal waves against air on two interfaces. This is a reflection without an AR coating.}}
}}

Indices of refraction for a range of materials can be found in the [[list of refractive indices]].