Talk:Eyeglass prescription

message: This section is a misnomer in that 5 of the 9 items discussed are not abbreviations. This needs to be changed. Edwardian 16:07, 19 August 2005 (UTC)
thread_title: Abbreviations

message: Repost of my question on Talk:Visual acuity: Please include some explanation of how diopter measurments fit into this. I'm looking for a rough equivalent of the measurements used in this article and diopter measurements (which will have to be +/- becuase acuity does not determine myopia vs. hyperopia). Maybe a table with some standard acuity values (e.g. 20/20, 20/40, ... 20/400) and their equivalent diopter ranges?  For example, it seems to me that 20/30 is equivalent to a +/- 1 diopter prescription. Kslays 16:10, 1 May 2006 (UTC)
thread_title: [[Diopter]] vs. [[Visual acuity]]

message: First, I would like to commend the fact we have an expert who contributed to this topic.
Second, if we were to write a Simple English version of this article, what would we include and not include? I feel that a Simple English article would be helpful here, as some of the optometry is beyond what a Simple English reader might want to read.
Guroadrunner 06:47, 4 June 2006 (UTC)
replies: text: i don't believe that the concepts being discussed can discard the technical jargon, but if there is terminology that is confusing, i think a more thorough explanation would be appropriate.  if anything is still unclear, ask here and i'll work up an explanation for the layperson. Coffee joe (talk) 05:17, 13 June 2008 (UTC)
thread_title:  Simple English version? 

message: What is the manufacturing process in making the lenses?
well, i make lenses so i can answer that, but i believe it's a little out of the scope of this article.  also i'm not sure that the topic is 'encyclopedic' in nature.  if anyone convinces me otherwise, i'd be happy to create the article.
basically liquid resin is injected into a mold and the product after hardening the resin is a lens that's ready to be cut down to the shape of the frame (a 'finished' lens), or a 'semi-finished' lens. a semi-finished is made thicker so that be back can be cut away to the shape required to make the lens the desired power. it is then put on a series of machines that rub it against laps to create the final back curve(s).  one to rough it in and the second to polish it.  then it is 'edged' (cut down) to the shape of the frame so it can be mounted.
i wouldn't be sure how to organize that into an article or know what info to include or exclude, and like i said i'm not sure it's appropriate for an encyclopedia.
Coffee joe (talk) 04:54, 13 June 2008 (UTC)
thread_title:  Manufacturing 

message: First, let me say that this page does an excellent job of explaining what are in fact quite complex concepts in an understandable way. I wear glasses, and I didn't know half this stuff. That said, some of the language is a bit too casual (widespread use of second person, etc.) and a good copyedit would clean it up real nice. I will try to do that in the next few days; feedback would be appreciated. 216.193.172.224 00:50, 13 September 2006 (UTC)
thread_title: Editing

message: It should be noted, somewhere, that the human visual system actually has more degrees of freedom than an eyeglass prescription represents, which is one reason (although not the only reason) why some people's vision is considered "uncorrectable".  In such a case, the vision is not really uncorrectable in principle, but the required lenses would be uneconomical or otherwise impractical to fabricate.  121a0012 (talk) 05:25, 30 April 2008 (UTC)
replies: text: Can you elaborate on what you mean by "degrees of freedom"?Garvin  Talk 03:51, 10 May 2008 (UTC)
replies: text: The same thing as is normally meant (see the article).  121a0012 (talk) 05:06, 10 May 2008 (UTC)

text: Which other degrees of freedom do you have in mind? Obviously if a person's lens were rough, it would be uncorrectable by conventional glasses, but I don't think that's what you mean. —Ben FrantzDale (talk) 02:52, 24 May 2008 (UTC)
replies: text: One could, for example, require two cylinder corrections (in different axes, obviously), rather than the one which is normally available.  Or the shape of the lens or the retina could be asymmetric in some other way.  (Or perhaps they could be perfectly radially symmetric, but about an axis that is not centered.)  121a0012 (talk) 23:01, 24 May 2008 (UTC)
replies: text:  While you could in principle make arbitrary lens geometry involving aspheric lens elements, I believe that the idea of multiple cylindrical corrections in one lens is overly complicated. Assuming the lens will have a smooth surface, then the local curvature at any point is completely defined by a spherical and cylindrical component and an orientation. That is, locally the surface of a lens will look like the surface of an ellipsoid: you can't have a smooth surface with curvatures in more than two directions. (See Curvature#Two dimensions: Curvature of surfaces and Principal curvature.) I may not be explaining this well. Do you have any references that describe what you are talking about in more detail? —Ben FrantzDale (talk) 19:12, 26 May 2008 (UTC)
replies: text:  The only reference I have is the demonstration given to me by my optometrist of why my vision is uncorrectable.  (As an aside: You appear to be using the word "smooth" in some technical sense that isn't readily obvious to me.)  121a0012 (talk) 03:14, 27 May 2008 (UTC)
replies: text:  Interesting. I'm sorry to hear that. I won't question your optometrist's professional opinion, but from the optics perspective, I don't quite understand your explanation; I would be fascinated to see a detailed explanation if you can find one. (When I said "smooth", I was sloppy; meant what mathematicians call C^2 continuous which means that the radius curvature of a surface changes smoothly as you move along it. The result of that is that at every point, such a surface can be described by a curvature in two directions, but not more than two directions. This is the kind of smoothness you'd get if you grab the ends of a stick and bend it; to contrast, a strait line leading into a half circle is only C^1 continuous—the curvature changes suddenly but the line is "smooth" in that it makes no sudden change in direction.) —Ben FrantzDale (talk) 11:19, 27 May 2008 (UTC)
replies: text:  The optometrist has a handheld device that fits over the bridge of the nose, which is similar to the larger device used for ordinary examinations but with the distinction that the cylinder element freely rotates on a handle the user can adjust.  (I don't recall whether the power of the cylinder correction could be so adjusted -- presumably by moving the lens normal to the axis of rotation).  It was quite clear after a minute or so that no rotation of the cylinder would bring the entire field of view into focus.  The optometrist selects the (cylinder power, axis) pair that bring the center of the field as close to focus as possible, but in my case that leaves most of my FoV out of focus (in that eye, anyway -- the miracle is that the brain can still make use of both eyes to generate depth perception even when one is mostly out of focus.  "Degrees of freedom" would be the obvious mechanical analogy for me to express that the dimensionality of my prescription is not sufficient to fully correct my vision.  121a0012 (talk) 02:53, 28 May 2008 (UTC)

text:  astigmatism is only one kind of optical aberration, some others being foil and coma, all of which can be compound. there are some new lenses on the market that are ordered custom directly from the manufacture that can correct for these kinds of aberrations, but only in the center of the lens, creating a 'sweat-spot' in front of the eye. the doctor perscribing these lenses has to have an instrument from the manufacurer that will analize the aberations in your eye so they can have a 'map' of the aberrations to be corrected. it isn't widely available though because not many doctors want to bother with a new piece of equipment with such a narrow use. Coffee joe (talk) 05:09, 13 June 2008 (UTC)
thread_title:  Degrees of freedom 

message: I believe that, in the US at least, a contact lens prescription expires after about a year.  If someone has a cite for this, I think this would be useful to add, along with an explanation.  --Mdwyer (talk) 06:08, 22 June 2008 (UTC)
thread_title:  Importance of Expiration Date 

message: The distance between the retina and the lens would seem to have some impact on the diopter numbers.  That is, I've had prescriptions for glasses, contact lenses, and finally an implanted IOL, and their diopter numbers are significantly different, ranging from -9 to -13.  How is this handled in a prescription? --Mdwyer (talk) 06:08, 22 June 2008 (UTC)
replies: text: I don't know. I would imagine that one prescription would describe what lens you need no matter if it is in the eye, on the eye, or near the eye. Making the thin lens approximation, and assuming the corrective lens is near the eye (for some definition of near), the distance to the eye shouldn't matter: the lens just needs to have the power so that it's power in diopters plus your eye's lens power in diopters brings the rays into focus on the retina. That said, I am not an optometrist. —Ben FrantzDale (talk) 06:27, 22 June 2008 (UTC)
replies: text: well, you're right and your wrong.  the prescription that most people are familiar with is their spectacle prescription.  this prescription typically assumes a vertex distance of 14mm.  that is the distance from the front of your cornea to the back surface of the lens.  14mm is an approximate average for glasses and is the distance most refractionists operate the phoropter from.  however if you were your glasses significantly closer or farther from your face the actual power of the lens used may be converted to the correct effective power.  in this way that one prescription can "describe" the correction that you need.  for contact lenses the vertex distance is obviously 0 and must be converted to have the same effective power.  in the case of an i.o.l. the vertex distance is negative and must be further compensate.  in the case of i.o.l.s used to replace the eyes original crystallin lens. the power of the original lens itself must be factored into the final power of the lens to be implanted. btw, that article about vertex distance is awful and not entirely correct.  i just found that and may have to work it over but i link to it for at least some reference. Coffee joe (talk) 09:59, 9 July 2008 (UTC)
thread_title:  Difference between Glasses, Contacts and IOL 

message: There seem to be a few stub articles that deal with different aspects of prism correction. I propose that the following articles should be merged: Prism dioptre, Prentice's rule, and Prentice position. Perhaps there are more that I am missing? I'm thinking that Prism correction would be a good title for a merged article, but editors of this article may have other ideas, or perhaps it would be better to merge the articles here. I'll forward all discussion to this section, so it can be all in one place.--Srleffler (talk) 17:30, 8 March 2009 (UTC)
thread_title:  Merge articles on prism correction 

message: The vieweing direction is specified for the cylinder correction. However, the definition of LEFT and RIGHT for the eyes is not clear. The standard medical definition of Left and Right is from the patients perspective; following this principle, the Left eye is on the same side as my Left hand. If, however, we apply the same principle as for the cylinder axis, my Left eye in the prescription is actually my Right eye because then Left is the left of the optometrist, and not my Left. Is it please possible to clarify this right in the beginning?  —Preceding unsigned comment added by 88.193.112.185 (talk) 18:25, 7 June 2010 (UTC)
thread_title:  Who's left/right? 

message: Did this get munged in editing?
It says "Both of them show the same information, namely a power of +2.00 diopters at the 90th (vertical) meridian and +3.00 diopters at the 180th (horizontal) meridian:"
and "The result in both cases is +2.00 diopters at the 150th meridian and +3.00 diopters at the 60th meridian."
Isn't the second statement the correct one, or do they refer to something different? 
Archangle0 (talk) 19:57, 10 March 2011 (UTC)
thread_title:  Variations in prescription writing 

message: Loved the article. Well Done. 
----  — Preceding unsigned comment added by Maheshsinghjoshi (talk • contribs) 13:53, 15 October 2011 (UTC)
thread_title: Comment

message: I have removed "Opticians are not eye doctors and, therefore, are not licensed to write an eyeglass prescription." Later in the paragraph optometrists are said to write eyeglass prescription. And they are not doctors. So the removed text cannot be right. Paul Beardsell (talk) 22:33, 18 September 2015 (UTC)
thread_title:  not a doctor and *therefore* 

message: Spherical lenses have a single power in all meridians of the lens, such as +1.00 D, or −2.50 D.
Astigmatism, however, causes a directional blur. Below are two examples of the kind of blur you get from astigmatism. The letters are smeared out directionally, as if an artist had rubbed his or her thumb across a charcoal drawing.
A cylindrical lens of the right power and orientation can correct this kind of blur. The second example is a little bit more blurred, and needs a stronger cylindrical lens.
But notice that in addition to being smeared more, the second example is smeared out in a different direction.
A spherical lens is the same in all directions; you can turn it around, and it doesn't change the way it magnifies, or the way it blurs:
A cylindrical lens has refractive power in one direction, like a bar reading magnifier. The rotational orientation of that power is indicated in a prescription with an axis notation.
The axis in a prescription describes the orientation of the axis of the cylindrical lens.  The direction of the axis is measured in degrees anticlockwise from a horizontal line drawn through the center of a pupil (the axis number can be different for each eye) when viewed from the front side of the glasses (i.e., when viewed from the point of view of the person making the measurement).  It varies from 1 to 180 degrees.
In the illustration below, viewed from the point of view of the person making the measurement, the axis is 20° if written in plus notation or 110° if written in minus notation. (20° and 110° being perpendicular to each other.)
The total power of a cylindrical lens varies from zero in the axis meridian to its maximal value in the power meridian, 90° away. in the example above the axis meridian is located in the 20th meridian, and the power meridian is located in the 110th meridian.
The total power of a lens with a spherical and cylindrical correction changes accordingly: in the meridian specified by axis in the prescription, the power is equal to the value listed under "sphere". As you move around the clock face, the power in a given meridian will get steadily closer to the sum of the values given for sphere and cylinder until you reach the meridian 90° from the meridian specified by the axis, where the power is equal to the sum of sphere and cylinder.
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The above section has been removed.  The information is better incorporated into corrective lens, as it is more a discussion of correction and optics rather than the components of an eyeglass prescription. Garvin  Talk 19:40, 31 October 2017 (UTC)
thread_title: Axis

message: The DV portion of the prescription describes the corrections for seeing far away objects. The NV portion is used in prescriptions for bifocals to see very close objects. For most people under forty years of age, the NV or near-vision portion of the prescription is blank because a separate correction for near vision is not needed. In younger people, the lens of the eye is still flexible enough to accommodate over a wide range of distances. With age, the lens hardens and becomes less and less able to accommodate. This is called "presbyopia"; the presby- root means "old" or "elder". (It is the same root as in the words priest and presbyterian.)
The hardening of the lens is a continuous process, not something that suddenly happens abruptly in middle age. Though it is typically by the middle age when the process has progressed to the point where it starts to interfere with reading. Therefore, almost everybody needs glasses for reading from the age of 40–45. Because young children have a wider range of accommodation than adults, they sometimes examine objects by holding them much closer to the eye than an adult would.
This chart (which is approximate) shows that a schoolchild has over ten diopters of accommodation, while a fifty-year-old has only two.  This means that a schoolchild is able to focus on an object about  from the eye, a task for which an adult needs a magnifying glass with a magnification of about 3.5.
The NV correction due to presbyopia can be predicted using the parameter age only. The accuracy of such a prediction is sufficient in many practical cases, especially when the total correction is less than 3 diopters.
When someone accommodates, they also converge their eyes. There is a measurable ratio between how much this effect takes place (AC:A ratio, CA:C ratio). Abnormalities with this can lead to many orthoptic problems.
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The above section deals almost exclusively with the topic of presbyopia.Garvin  Talk 21:47, 31 October 2017 (UTC)
thread_title:  Distant vision (DV) and near vision (NV)