Talk:Corrective lens

History?

How about some historical information? —Preceding unsigned comment added by 96.234.251.124 (talk) 15:08, 1 September 2010 (UTC)

Another vote for some more historical information. — Preceding unsigned comment added by 134.225.121.221 (talk) 10:07, 27 January 2012 (UTC)

Historical information can be found on the glasses page and the contact lens page.Garvin ^Talk 16:49, 2 August 2013 (UTC)

Comments

Some of the explanations need better wording and more accurate descriptions. Maybe someone more knowledgable can help in this regard.MichaelGoldshteyn 14:48, 8 September 2006 (UTC)

I've tried with recent edits. Are there specific areas that need attention now?Garvin (talk) 10:19, 13 January 2008 (UTC)

Most people do not seem to be bothered by a slight or even moderate amount of chromatic aberrations. However, the choice of material and index are the only criteria that are available to the average consumer. Best base curve selection and even selection of aspherics and atorics for all material types are usually not provided as options to opticians, let alone consumers. Such decisions lie solely with the lab producing finished and semi-finished blanks.MichaelGoldshteyn 14:48, 8 September 2006 (UTC)

Removed this text added by 155.136.80.163: "Polycarbonates are typically manufactured from sheeps' bladders, which contain a specific diamino - benzoic acid molecule, relatively low in molecular weight, but relatively unwearing." which appeared under High-index materials (Polyurethanes) heading, since:

• It has nothing to do with polyurethanes, as stated
• If true for polycarbonates, which I doubt, since they are synthetic plastics, it should be added to the page on polycarbonates not corrective lenses.

MichaelGoldshteyn 15:27, 12 September 2006 (UTC)

Undid the change made by 71.136.6.98, who changed the Fraunhofer line type from the correct He to the incorrect Na. Clearly, said user did not go to the Abbe Number link and read about which Fraunhofer line is used for Abbe number references in the US (i.e.,He-D3 or more commonly the d-line, with respective Abbe number V_d ) and Europe/Japan (i.e., Mercury e-line with respective Abbe number V_e ).
References, in order of authority:

• ISO 7944:1998 (Can be purchased in PDF form from ISO)
• Article on optical standards
• 20/20 High Index Primer article
• Optiboard forum discussion of the topic

MichaelGoldshteyn 16:31, 3 October 2006 (UTC)

Q: Polycarb lenses are supposed to be more scratch resistant than most lenses according to other sites. The article states that polycarb lenses scratch more easily than most lenses. Can someone check this?

A: Polycarbonate in and of itself is not very scratch resistant. It is the hard scratch resistant coating that is almost always applied to the polycarbonate that gives it the scratch resistance often found in lenses made from the material. The reason that uncoated polycarbonate scratches easily is that it is a very soft material. This softness is what gives it much better impact resistance, since it bends rather than breaks. However, it is this same softness that makes polycarbonate easy to scratch by harder materials. See polycarbonate and also http://www.engineeringtalk.com/news/gad/gad192.html for more information. MichaelGoldshteyn 20:15, 19 December 2006 (UTC)

Aspheric lenses are not only for cosmetics, they provide better "picture". At least stright lines looks stright.

Curtis Williams, please correct your assertion that: This qualification is necessary since best-form spherics are always better than aspherics for an ophthalmic lens application. This assertion is incorrect! MichaelGoldshteyn 17:14, 25 January 2007 (UTC)

 What quality of lenses can be expected at "discounters" such as Lense crafters and wal-mart etc>?

Sphere "axis", irregular astigmatism

The axis defines where the two powers (sphere and cylinder) are located. The sphere is almost always 90º from the cylinder. (This is regular astigmatism, which is by far more common than irregular astigmatism where separations are other than 90º).

This is garbage! A sphere has no axis (besides the optical axis which points normal to the lens surface or into the paper plane of the diagram referred to here). Irregular astigmatism is somewhat a misnomer by ophthalmologist, as in a wavefront sense, "regular" astigmatism is simply the lowest order even aberration (does not change sign on the opposite side of the pupil) that can be corrected by a "cylinder", anything that does not fit in that scheme and causes "blurring" is called "irregular" astigmatism by ophthalmologists, while more correctly, different (higher) orders of coma (odd symmetry), astigmatism (even symmetry) and even higher oder spherical aberrations can appear, but the irregularity here is not related to any orientational angle.

However, it is known that in a typical population, certain orientations of regular astigmatism are more common than other ones. Maybe this kind of irregularity was meant here, but it´s not the usual meaning of that term. —Preceding unsigned comment added by 84.174.203.127 (talk) 22:26, 27 March 2008 (UTC)

This comment raises some good points. An effort should be made to describe things both in terms of physical optics and vision correction. It is better to bridge these fields of study than to isolate them. Garvin ^Talk 16:53, 2 August 2013 (UTC)

Best form vs. free form

This qualification is necessary since best-form spherics are always[verification needed] better than aspherics for an ophthalmic lens application.

This cannot really be true in the strict mathematical sense, because mathematically, the spherical "best form" is only one special case of the a general "free form" surface. So, a "best form" is a restricted "free form" surface, hence, you reduce the number of available degrees of freedom to solve the problem at hand. With less number of free parameters, the result cannot be better than a more general solution. However, for reasonable metriks, it is true, that a flatter "free form" is likely not as good as the more curved spherical "best form"! 195.127.179.227 (talk) 15:34, 30 January 2008 (UTC)

Trademarks

Reminder to editors: per Wikipedia:Manual of Style (trademarks), the trademark symbols ™ and ® should not generally be used in Wikipedia articles. Trademarked names are rendered using standard English text formatting and capitalization, without special marks or symbols. More info in the linked Guideline. --Srleffler (talk) 19:12, 15 June 2008 (UTC)

Manufacturer of MR-10

Google results show that MR-10 is made by Mitsui Toatsu in Japan. Seiko seems to be using the MR-10 material. Shouldn't that be listed in the chart as opposed to leaving it blanc?24.83.148.131 (talk) 09:23, 21 June 2008 (UTC)BeeCier

Wrong diagram

This diagram from the section "Abbe number" was combined with the caption "The effect of changing the spherical form of the lens on chromatic aberration". The diagram is not of a lens with a differing "spherical form", it is a diagram of another lens type, an Achromatic lens, not talked about in the article. Fountains of Bryn Mawr (talk) 16:28, 13 October 2009 (UTC)

Achromatic eyeglasses?

Does anyone make achromatic eyeglasses to correct chromatic aberration at high lens diopters (+/- 10)? I am aware that these would look odd and be rather thick, but would also result in extremely good color acuity. DMahalko (talk) 02:09, 9 May 2010 (UTC)

TV / CRT implosion band?

There is something interesting that comes to mind, when discussing shattering of eyewear. Cathode ray tubes typically include a tensioned steel band around the front of the screen, which helps to strengthen the glass and support it during an impact event.

Could a tensioning band strengthen eyewear against blunt impact? Could lenses be made much thinner yet with a structural band around the outer edge?

For this to work the band would have to be so tight that it compresses the lens slightly, and probably would have to be separate from the eyeglass lens mounting.

DMahalko (talk) 07:01, 9 May 2010 (UTC)

Typography: x versus ×

I see "−1.00 +0.25 x 180" in the text. Is that correct or is that a "times" symbol like this: "−1.00 +0.25 × 180"? —Ben FrantzDale (talk) 12:20, 2 September 2010 (UTC)

Both are correct. When handwritten, it is the same mark as the letter "x". Digitally, most people type the letter "x" because it is easier. The "times symbol" × is not inaccurate, though there is no multiplication that should be implied by its use.Garvin ^Talk 17:00, 2 August 2013 (UTC)

Aspheric advantages self-evident or need citation?

I would like to see citations to studies (if there are any) which show the objective and subjective acceptability of aspherics. I have +6.75D -1 cyl. I had spectacles made up some years ago on the understanding they were high index aspheric. Three lens changes later, I ended up with a very acceptable lens (on the understanding they are high index aspheric). Meanwhile, I have tried repeatedly to achieve the same excellent result with various other ophthalmologists and high index aspheric lenses with no success. I have since taken a side picture of these good lenses, then matched the profile perfectly to a circle. My conclusion is that my original ophthalmologist changed the lens to flattened high index spheric without my knowledge. My conclusion is that aspheric lenses are not suitable for all eyes or all prescriptions. In my experience, aspherics have created unacceptable chromatic aberration and mis-focusing 15+ degrees off the direct line of sight, to the point where I feel driving would be dangerous.Nick Hill (talk) 08:38, 9 September 2011 (UTC)

That's an interesting question. I don't know if I have aspheric lenses or not, but I do know that in general imaging-lens design, aspheric surfaces do more than just one thing. That is, I suspect an aspheric corrective lens could be used to create a flatter lens, trading off-axis image quality for ability to fit the right on-axis prescription in a big frame (e.g., I have a pretty powerful perscription in aviator frames and don't have coke-bottle edges). Alternately, an aspheric lens could be designed to give optimal image quality across the field. I would be very curious to know more about how an optician goes from a perscription and a frame to the geometry of the "glass". I know more or less how it works for imaging-lens design, but eyeglasses are different in that your eye moves around.

As for lateral chromatic aberration, I sometimes wish I could request an achromatic doublet, but I bet that would be very thick.

Also interesting would be to know about aspheric contact lenses. Contacts should make correction easier because the corrective lens is fixed WRT the eye, so an aspheric contact could, I think, provide correction of higher-order optical aberrations than could eyeglasses, e.g., correcting spherical aberration (which isn't what the spherical component does, BTW; that corrects astigmatism). —Ben FrantzDale (talk) 12:12, 9 September 2011 (UTC)

Since my original note, above, I have since had spheric lenses made up in a similar frame size, and am happy with the result. This adds weight to the suggestion that the aspheric trade-off may not be acceptable to many, although many opticians now err towards aspheric for my prescription.Nick Hill (talk) 23:58, 13 December 2011 (UTC)

As far as I know, aspheric lens are not used "for flattening the lens", which is a nice side-effect but not the real reason.

It seems that lens are rendered aspherical in order to keep the prescription/correction even when the eye is not fixated on the center of the lens. Indeed, the ophtalmic glasses are designed so that the optical center of the lens is aligned with the cornea and other eye parts as long as the eye is centered (as you look right in front of you). When you look sideways without moving your head, the eye is no more aligned with the lens; variations from the initial correction may occure with spherical lenses (and this, even for movement of few degrees).

To allow a more uniforme correction for the eye, whatever the direction the eye is looking at, aspherical lenses are used.

However, as noted above, aspherical lenses have, as a trade-off, more chromatisme for the rays that come from the "aspherical parts of the lens" when the eye is centered.

Further, the quality of the aspherical lens depends greatly on the accuracy of the optician with regards to defining the center of the lens, positioning it exactly in front of the eye, his measurement of the distance between the eye and the lens....etc (which explains why one can have aspherical lenses that are less good than spherical lenses).

Progressive lenses are a kind of aspherical lenses. In this case the lens is not spherical and the focal point of the lens evolves along a vertical axis, allowing "long vision" at the top, "intermediate vision" and "reading vision" at bottom. One cannot say the progressive lenses have lower quality than monofocal aspherical lenses. However, generally the terme "aspherical" is used do speak about focal point variation along a longitudinal axis (when the eye moves to the right to the left) (and the variation are generaly less drastic than the one used for progressive lenses). Calavente (talk) 13:11, 26 January 2012 (UTC)

explanation of spherical, cylindrical, and axis TOTALLY UNCLEAR.

The description & definition of the terms spherical, cylindrical, and axis, including having terms like 'meridian' etc., mixed in, is totally USELESS. Maybe if the reader is an optometrist and already understands the terms, it may make sense...but I am a physicist, I've studied and used optics (microscopes, telescopes, particle accelerators!), but the 'explanations' presented here make no sense, the terms are defined circularly. How about some drawings which clearly show the relationships of these quantities that any high school student (who has had geometry) can understand clearly? As another reviewer said, a sphere has no axis (until you define it, or rotate it..). The terms are defined as someone working in the field would define them for incoming students, but there is no connection to fundamental mathematical definitions. — Preceding unsigned comment added by 62.167.120.140 (talk) 13:49, 23 March 2013 (UTC)

I'll take a look. True, the terminology used is that of the optical industry. I'll try to improve things a bit. (See my answer above)Garvin ^Talk 17:02, 2 August 2013 (UTC)

Aspheric section removed

I removed the following section:

===Aspheric=== Aspheric lenses are typically designed to give a thinner lens, and also distort the viewer's eyes less as seen by other people, producing better aesthetic appearance. Older texts may refer to lenticular lens polynomial designs, and advantages of curvatures that do not produce Scotoma, or a blind spot.

It was poorly written and not pertinent to the article; at least not in the location I removed it from. An update to discuss the latest lens technologies and how they differ from the traditional types described could include some of this information about aspheric lenses. If someone can improve the section, the information could be re-inserted into the article. Garvin ^Talk 16:08, 2 August 2013 (UTC)

I haven't altered any of the content. However I would like to point out that it's spurious.

Confusing corrective lens industry terminology[edit]

Spheric vs. aspheric, atoric, etc.[edit] Lens manufacturers claim that aspheric lenses improve vision over traditional spheric lenses. This statement could be misleading to individuals who do not know that the lenses are being implicitly compared to "a spheric flattened away from best-form for cosmetic reasons".[verification needed] This qualification is necessary since best-form spherics are always better than aspherics for an ophthalmic lens application.[2] Aspherics for corrective lenses are only[verification needed] used to attempt to improve the degradation caused by deviating from best-form sphere resulting from making a flatter lens for cosmetic reasons. The same applies for atoric and bi-aspheric.

It is true that aspheric lenses are used in cameras and binoculars. It would be wrong to assume that this means aspherics/atorics are a sign of good optics in eyewear. Cameras and telescopes use multiple lens elements and have different design criteria. Spectacles are made of only one ophthalmic lens. The best-form spheric lens has been shown to give the best vision.[citation needed] In cases where best-form is not used, such as cosmetic flattening, thinning, or wrap-around sunglasses, an aspheric design can reduce the amount of induced optical distortions.[citation needed]

The problem with aspheric lenses is that they are a broad category. A lens is made of two curved surfaces, and an aspheric lens is a lens where one or both of those surfaces is not spherical. Further research and development is being conducted[citation needed] to determine if the mathematical and theoretical benefits of aspheric lenses can actually lead to better vision correction.

My suggestion would be to scrap the section. Or to change it to say that *some* designs of aspheric lens are aimed to, primarily, reduce lens thickness, whereas other designs aim to improve vision. I should point out that the Coddington shape factor only allows for the minimisation of third order spherical aberrations. Whereas the ideal hyperbolic lens if free from all axial aberrations. — Preceding unsigned comment added by 82.26.243.115 (talk) 17:47, 14 January 2015 (UTC)

Proposal: Move information to Glasses

The term Corrective Lens applies to any form of corrective lens. (See the introductory paragraph of this article.) The second half of the article discusses topics that apply only to spectacle correction (glasses). I plan to incorporate that information into the glasses article and eliminate the redundancy here, as a link to the glasses article should suffice. Send a message to my talk page if you disagree. Garvin ^Talk 16:46, 2 August 2013 (UTC)

4 years later, this information still seems out of place, but the glasses article does not seem more suited to contain it. Probably best to just leave all the technical stuff here and leave the glasses article as information about the societal importance of eyewear. Garvin ^Talk 16:40, 27 October 2017 (UTC)

Holding place for information taken from glasses

This information may already be present in the article.

Eyeglasses normally correct and compensate for four types of vision deficiencies:

• Myopia is a vision disorder that causes far objects to appear blurred but near objects to be seen clearly. Individuals suffering from myopia are prescribed eyeglasses with concave lenses, which compensate for the refraction error by moving the image of the distant objects that cannot be seen clearly backward onto the retina.
• Correcting hypermetropia is normally done with eyeglasses with convex lenses. With this disorder, the patients can see distant objects clearly but they have trouble with seeing objects that are close to them. Eyeglasses with convex lenses compensate for the refraction errors by moving the image of a nearby object that cannot be seen clearly forward onto the retina.
• Astigmatism is typically corrected with a cylindrical lens. This disorder is caused by a non-uniform curvature in the refractive surfaces of the eye, which leads to an abnormality in focusing the light rays on the retina. As a result, a part of the light rays are focused on the retina and the other part is focused behind it or in front of it.
• Presbyopia is a condition where the eye exhibits a progressively diminished ability to focus on near objects with age. It is more frequent in people over 40 years old and it is corrected with convex lenses. These patients need reading or bifocal eyeglasses.

Corrective eyeglasses can significantly improve the life quality of the patient as they are helpful in both correcting vision disorders and reducing problems that appear when such lenses are needed, such as headaches or squinting. A small amount of time is needed to adapt to the new lenses, usually 1–2 weeks.

Corrective lenses can also be added to work masks or eyeglasses used in sports.

Eyeglass lenses are commonly made from plastic, including CR-39 and polycarbonate. These materials reduce the danger of breakage and weigh less than glass lenses. Some plastics also have more advantageous optical properties than glass, such as better transmission of visible light and greater absorption of ultraviolet light. Some plastics have a greater index of refraction than most types of glass; this is useful in the making of corrective lenses shaped to correct various vision abnormalities such as myopia, allowing thinner lenses for a given prescription.

Scratch-resistant coatings can be applied to most plastic lenses giving them similar scratch resistance to glass. Hydrophobic coatings designed to ease cleaning are also available, as are anti-reflective coatings intended to reduce glare, improve night vision and make the wearer's eyes more visible.

More Trivex Info

I added the paragraph "Trivex was originally developed for the military, as visual armor. PPG Industries took the technology andadapted it for the optical industry. Trivex is a urethane based pre-polymer. PPG named the material Trivex because of its three main performance properties. The three main properties are superior optics, ultra light weight, and extreme strength." from the paper at triple w dot uccs.edu/~rtirado/trivex_lens.pdf . I did not change the glasses article. Just here, because I was not sure if copying a paragraph directly is allowed by Wiki.173.180.7.3 (talk) 12:17, 10 December 2013 (UTC)BeeCier

173.180.7.3, something that would be useful is reliable sources that we can cite. For example, in this edit you mention that Trivex is or was used for fighter jet canopies. It would be great if there's a source for that, particularly if it reports the date it was created. Today I updated the Trivex section and had to guess at the 1994 date. The source I used says "Four years after CR 39's 50th anniversary"^{[http://www.eyecarebusiness.com/articleviewer.aspx?articleID=50369} and as CR-39 is reported as being developed in 1940 I guessed Trivex came out in or around 1994. That source also says it was "transparent armor". FWIW, that source also has that PPG developed CR-39. Is that true? Google for "transparent armor" term nothing that looked like a useful source. I did not try to chase down the connection between PPG and CR-39. --Marc Kupper|talk 21:44, 21 January 2017 (UTC)

self correction own page

Should self correction have its own page? -- it is a subtopic to this page- but does not fit well with the others --- there is quite a lot of literature on the topic and I know at least one company selling them commercially.--Currystove3 (talk) 03:20, 11 February 2015 (UTC)

Merging from Glasses

An enormous amount of material is duplicated from this article on Glasses. The content has diverged, and I am trying to merge carefully, but I just did the section "Ophthalmic material property tables" and accepted the content of the other article en masse because it looked more updated and it is difficult to check everything completely. Editors of this article may wish to check this section for accuracy and check the edit history to see if any changes should be restored. Thanks! -- Beland (talk) 19:16, 23 August 2016 (UTC)

Convex lenses and concave lenses

This article could make it clearer how there are concave lenses and convex lenses and how one type of lens corrects short-sightedness and one type corrects long-sightedness (I can never remember which is which!) Vorbee (talk) 08:46, 23 October 2017 (UTC)

Those topics are better discussed in Lens (optics), but perhaps links to that article would be appropriate. The reason I say that is that nearly all forms of corrective lenses are ophthalmic: a convex front surface and a concave back surface.Garvin ^Talk 16:11, 27 October 2017 (UTC)

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