Talk:Visual acuity

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I forgot to put the change's name when I added the snellen card to the page. :)

Contents

[edit] Remake article

I feel that the article has a lot more to say about visual acuity. Also it can be reorganized to structure it a little more. I will work on it in the following days if is there no objection.

Go for it! (Please sign your user name with ~~~~ .) AED 18:05, 22 December 2005 (UTC)
Ok. Didn't know how. :) Rafael Sepulveda 20:41, 23 December 2005 (UTC)

[edit] Add some things...

Do you think it is important to mention the tecnique of measuring visual acuity? Because nothing is being mentioned about that, and also nothing is being mentioned of near visual acuity and pin hole. But the article is growing a lot by now....

Rafael Sepulveda 20:45, 23 December 2005 (UTC)

I think all of the above should eventually be added. Keep up the good work! AED 21:54, 23 December 2005 (UTC)

[edit] Maximum visual acuity

RE: "the average visual acuity of healthy eyes is 20/16 or 20/12". I'm wondering if we should clarify this a bit more. "Healthy" in what sense? No refractive error or free from disease? [split post - see below]

It's about free from disease and refractive error; I will change it to be more specific. Rafael Sepulveda 07:12, 24 December 2005 (UTC)
Should we also include mention that some corrected ametropes can achieve those acuities, too? AED 20:00, 24 December 2005 (UTC)
Some corrected ametropes, some corneal transplanted, and retinal surgery (any many more) can achieve this VA, even more. The measurement is to discriminate what is "normal" and what is not. I think is irrelevant to mention the specific cases where it is attainable. Let's only mention what is the "normal" VA regardless the way it is attainable. What do you think?
I think “normal” is a bit ambiguous if left undefined, particularly since ametropia is a common finding in the general population and not really “abnormal”. To state that only healthy, emmetropic eyes are capable of seeing 20/20, 20/16, or even 20/12 is not entirely accurate. I do think it is relevant to mention that the measurement and notation of visual acuity in humans occurs in a given context (i.e. aided or unaided).AED 05:21, 27 December 2005 (UTC)
Added now. :) Rafael Sepulveda 05:42, 27 December 2005 (UTC)

[split post - see above] Should we mention something to the extent that the best attainable vision is based on the spacing of photoreceptors? [split post - see below]

This is not completley true. Of course that the photoreceptor density is important, but just up to the eye's optics quality, because if the photoreceptors were more close together the difraction phenomenon will not permit more visual acuity. Taking into account eye's optics, the best vision attainable is around 20/10 (even if you pack in the same space the double or triple quantity of photoreceptors). In my humble opinion, this topic is more of optics and eye's physiology rather than in a visual acuity article. What do you think? Rafael Sepulveda 07:12, 24 December 2005 (UTC)
I understand that photoreceptor density is not solely responsible that is why I added: "Visual acuity depends upon how accurately light is focused on the retina, the integrity of the eye's neural elements, and the interpretative faculty of the brain." I think the relevance to physiological optics and clinical optics are intertwined. Both types of articles will link here, so all relevant information you can add will be very, very helpful. AED 19:25, 24 December 2005 (UTC)
What I ment is that in a "normal" eye, the best optical resolution that can be achieved by the optical visual system is the same that can be registered by the normal density of photoreceptors; being more dense it's physiologicaly usless due to diffraction. I think we are discussing different things here... :) Rafael Sepulveda 01:27, 26 December 2005 (UTC)
I agree, so I’m not sure why you think we are discussing different things.AED 05:21, 27 December 2005 (UTC)

[split post - see above] You've alluded to it in the last sentence but perhaps we should state explicitly that having good visual acuity is not the same as having good vision. AED 22:17, 23 December 2005 (UTC)

Agree. Rafael Sepulveda 07:12, 24 December 2005 (UTC)
Similarly, I'm wondering if the "'Normal' vision" section should reitterate that the ability to resolve 1 arcminute at 20 feet is called "20/20" but that many (most?) emmetropes, and corrected ametropes, can resolve finer detail that equates to 20/16 to 20/12. AED 20:00, 24 December 2005 (UTC)
1 arc minute is a unit that is distant independant, so it's irrelevant to say it is at 20 feet, because at 20 kilometers will also be 1 arc minute. Initially Snellen took that as "normal" based in what Robert Hook said in the 17th century stating that a "normal" eye can discriminate 2 stars being apart by 1 minute of arc. Now we know that it is not necesarily true, but that was the standard taken to create that "20/20" figure. Either way I will put that in the article in the "normal" VA area. Rafael Sepulveda 01:27, 26 December 2005 (UTC)
Specifying distance is relevant when discussing the Snellen notation of 20/20, and reference to a Snellen notation was what I had mentioned. AED 05:21, 27 December 2005 (UTC)
I second that, 1 arc minute corresponds to the amount of space that hits the retina, doesn't matter if it is 1 cm or light years away. However someone with better acuity could resolve smaller angles. —Preceding unsigned comment added by 71.189.81.156 (talk) 02:31, 17 April 2008 (UTC)

[edit] emmetropia

I'm not pleased with the 'emmetropia' link to point to 'refractive error' page. Being this a complex subject (not a normal distribution graph, being that most people is lightly hyperope yet achieve 20/20, etc.) it should have it's own wikipedia page. What do you think?

“Emmetropia” should have its own article as long as it is not merely a definition of the term (per WP:WWIN). If you want to expand the article beyond a definition, go ahead and create it. I pointed the link to refraction error because that is currently the most appropriate place to find a definition of “emmetropia”; and that definition does not state that mild hyperopia equals emmetropia. AED 05:21, 27 December 2005 (UTC)

[edit] A lot added by now...

I've added a lot of things... maybe a little polishing will be needed. :) Also, near vision definition and the all the standard optotypes used have to be added. Any more things I'm missing? Rafael Sepulveda 09:40, 26 December 2005 (UTC)

Maybe mention of Jaeger notation and peripheral vs. foveal acuities. AED 05:21, 27 December 2005 (UTC)
Near visual acuity is being a lot difficult to find accurate, relevant information... still on the search. Rafael Sepulveda 08:53, 30 December 2005 (UTC)

[edit] Maximum VA vs. average VA

Do we have any references for maximum VA and/or average VA, aided or unaided, that we can include? I found one [1], but it doesn't state whether the students were aided or unaided. AED 05:57, 27 December 2005 (UTC)

Maybe this? [2] Rafael Sepulveda 08:46, 27 December 2005 (UTC)
I can't find anything to document that 20/12 or 20/16 is "average"? AED 00:20, 28 December 2005 (UTC)
It's just mentioned (no reference) in Duane's V.5 Ch.51 Rafael Sepulveda 04:14, 28 December 2005 (UTC)

[edit] Duane's

A lot of the statements in the History section appears verbatim in Duane's. Can you rewrite or paraphrase some of these statements so we don't violate WP:COPY? Thanks! AED 00:20, 28 December 2005 (UTC)

Working on it. Rafael Sepulveda 04:15, 28 December 2005 (UTC)

[edit] Contradiction

the maximum acuity of the human eye without visual aids (such as binoculars) is generally thought to be around 20/15 (6/4.5)

the average visual acuity of healthy eyes is 20/16 or 20/12

I don't know much about visual acuity, but one of these (maybe both, of course) is almost certainly false.

Depending on the studies made by different authors, it can be one or another (or even something else!). They're both approximate values and can't be stated precisely. Rsepulveda 08:52, 15 February 2006 (UTC)

[edit] Diopter

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? Kslays 15:55, 1 May 2006 (UTC)

What is -5.25 on the 20/20 scale?

I don't know, but "really bad" would be a reasonable first approximation. Worse than 20/300, I believe. --Zippy 05:07, 12 September 2006 (UTC)
Diopter measurement does not fit into visual acuity. They're different things. You cannot say that because someone has -1.00 diopters will see 20/50 or something like that. Also, there's a lot of people with a refraction of +5.00 that, without glasses, can see the 20/20 line.
A miopic (-1.00) person will, in theory, see the 20/10 line clearly at 10 feetmeters, but will not even see the 20/20 at 20 feet. This is because vision is impaired at distance, but in close range (less that 10 feet) will be perfect, like an emmetrope.
You should never try to calculate the refractive error based on visual acuity alone. It is only useful testing visual acuity to see if the refractive error is well corrected. Rsepulveda 10:47, 16 September 2006 (UTC)

Here is a table:

Dioptres 20/something
-0.5 20/25 to 20/30
-1.0 20/30 to 20/50
-3.0 20/300
-4.0 20/400
-5.0 20/600
Dioptres 20/something
+0.5 20/25
+1.0 20/40
+2.0 20/70
+3.0 20/100
+4.0 20/200

I understand this doesn't account for cylindrical (astigmatism), cataracts, or other problems, but a rough guide like this is very useful. -kslays 16:52, 19 June 2007 (UTC)

Would these tables fit into the article (or Diopter)? I see the 20/something descriptions of vision used often by North-Americans, but over here (NL), such measurements are never used, only the diopter value of the prescribed lenses. It'd be useful to have some way to compare the two systems, even if it's only a rough approximation. — Kimiko (talk) 05:59, 12 April 2008 (UTC)

[edit] Normal vision?

From the article:

A visual acuity of 20/20 is frequently described as meaning that a person can see detail from 20 feet away the same as a person with normal eyesight would see from the same distance. If a person has a visual acuity of 20/40, that person is said to see detail from 20 feet away the same as a person with normal eyesight would see it from 40 feet away.

What is meant by "normal eyesight"? 20/20? And if so, doesn't that make the first person meaningless, along the lines of a person with 20/20 vision can see as well as a person with 20/20 vision? Isn't there a less relative way of explaning this? Also, I don't think it's standard to use terms like "normal" in discussing physical conditions. Theshibboleth 05:37, 29 August 2006 (UTC)

I think the implied context of "normal eyesight" refers to vision unaffected by pathology or refractive abnormality. The article should probably state this more clearly. The last section of the article does attempt to clarify the non-relative meaning of 20/20 vision (i.e. the ability to resolve 1 minute of arc at 20 feet) and that its acceptance as "normal" visual acuity is somewhat relative. Clinically, however, it is standard to discuss conditions as "normal" or "abnormal". -AED 07:19, 29 August 2006 (UTC)

I did a web search a few weeks ago and found that somewhere between 60 and 80 percent of Americans wear corrective eyewear (with the general consensus being about 2/3rds). Something is wrong with the definition of "normal" if 2/3rds of the population don't reach it. Saying that 20/20 is the LOW end of "normal vision" also does not fit with that statistic. Just because vision is correctable to what we now call 20/20 or better does not mean that the original definition was correct. And although eyesight deteriorates in one's later years, I have not heard that it goes on a steady decline starting from the age of 18 like hearing does. By that statistic, 2/3rds of the population is unable to resolve 1 minute of arc at 20 feet. Doesn't that start to sound like an unrealistic standard of "normal" eyesight? (I will still need to use glasses even if we make that able to resolve 1 minute of arc at 15 feet or even 10 feet, but I wanted to comment on the use of the term "normal" in the entry.) "Normal" people in this country do not have "normal" eyesight. Perhaps we can keep the 20/20 standard and change the expression to "good" eyesight, while 20/16 would be "excellent" and 20/12 "exceptional." Then we can call 20/40 or 20/60 "normal."4.224.219.114 23:58, 29 June 2007 (UTC)

I think the phrase ""20-20 vision" refers to the distance in feet that objects separated by an angle of 1 arc minute can be distinguished as separate objects." is confused. If objects are separated by 1 arc minute (an angular measure) then distance shouldn't come into it. There's a problem with this definition. —Preceding unsigned comment added by 130.138.227.40 (talk) 13:51, 31 October 2007 (UTC)

Perhaps you're right - sort of. Certainly, the resolving power of an optic should be measured simply as a small anglular separation of two points distant from the viewpoint. But perhaps what you're missing is that in practice the human eye may lose its ability to maintain focus as the object is moved further away. When measuring the resolving power of a telescope the ability to focus may be taken as a given, but with the human eye it can't be. One problem with the 20:20 measure may be that people who are rather long sighted get a 20:20 or better rating even though they can't focus properly on an object at 10 inches. I don't know, I'm not ultra familiar with this measure's proper use.
You may (I don't know) be confusing resolving power with acuity (perhaps former assumes proper focus, the latter doesn't). I would actually like to see the article compare 'acuity' with 'resolving power'. This might be a useful comparison. —Preceding unsigned comment added by 83.67.127.181 (talk) 00:11, 28 April 2008 (UTC)

[edit] Star vision test

As many people are aware, a traditional test of visual acuity is the abilty to distinguish Mizar from Alcor, two stars in the big dipper. Given that the angle that separates them is about 12 minutes, what is the minimum visual acuity necessary to distinguish them (in terms of 20/x)? I was thinking about adding this to the Mizar article to quantify this "good vision" folktale once and for all. (Granted, it could be considered original research, but if it's only the result of some formula, it's probably not that bad, and I also really want to know.) 71.102.186.234 10:54, 26 November 2006 (UTC)

A 20/20 vision is defined as being able to discern the letters on the Snellen chart when they are 5 arc minutes at 480 lx illumination. Given the rather small differences between the P and F I'd say it's equivalent to discerning two point sources at 2 minutes. Then 12 minutes would be equivalent to 1/6th of 20/20, i.e. 3/20. However, the night sky is much much darker than 480 lx, such that you can't really compare these two measures. Han-Kwang 11:25, 26 November 2006 (UTC)

[edit] 20/0

Does 20/0 vision have any significant meaning? --Brandon Dilbeck 04:52, 13 May 2007 (UTC)

The short answer is no. The long answer is that the fractional description of visual acuity is really a way of writing it, and not a real fraction. What this fraction means, as the article says, is that the first number, or the numerator, is the standard distance of the optotype. The second number, or the denominator, is the relative distance as it is seen by a "normal", emmetropic person.

So, 20/0 should mean that an optotype placed at 20 feet, is seen with the clarity as being right in contact with the eye. To me, as an ophthalmologist, that doesn't says anything practical given the optics of the eye or the light that should be reflected by the optotype. It's meaningless.

I Hope I make my point of view clear (because I'm not an english native speaker :) ). Rsepulveda 22:17, 14 July 2007 (UTC)

I think you make your point clear. My understanding is that in maths you should always be very careful about using ratios to zero. Refer to 20:40 or 20:10 but not 20:0. You're right that 20:0 is nonsense. That's just comparing something with nothing. —Preceding unsigned comment added by 83.67.127.181 (talk) 23:47, 27 April 2008 (UTC)

[edit] 10/10 vision bad??????

OK, so I was reading Mad Magazine (specifically the Monroe section), and I run into this part where a man using a magnifying glass says "Damn 10/10 vision!" But wouldn't this be like saying "Damn 20/20 vision" or "Damn 20/18 vision"??????? What is 10/10 vision?????? 131.191.64.130 (talk) 02:59, 30 November 2007 (UTC)

[edit] Football coach?

Why does the last entry in the table in the History section link to a page about a football coach? Fixed.

[edit] LogMar

I'd disagree, based on my experience in an ophthalmology department, that the LogMar isn't used clinically. It's about 50/50 LogMar/Snellen now. Also, it doesn't just refer to a different way of expressing Snellen measurements, but a LogMar chart is also a completely different way. Should I add this into the article? Andrew Jacklin 15:47, 4 December 2007 (UTC)

I'd agree. Also, there is very little information about LogMAR on wikipedia. Could someone increase it a bit, maybe add a new page to talk about it? Snellen chart exists, so why not LogMAR chart? Also, it is not referred to as a Bailie-Lovie chart - the guys who invented the LogMAR chart [3] Ged3000 (talk) 19:20, 19 May 2008 (UTC)
As an extra - if someone is able to make those changes, the simulation chart at this website might be a useful link... Ged3000 (talk) 19:31, 19 May 2008 (UTC)

[edit] 20/20 and all that

It appears that the system that includes "20/20" is roughly a measure of the MTF cutoff of the visual system. Why is 20 feet the selected focal distance? I suppose that's reasonable for reading from a chalkboard, but couldn't a farsighted person have 20/20 vision and simply be unable to focus within arms length? Similarly, couldn't a slightly nearsighted person have 20/20 vision but have less than that angular resolution when attempting to focus at infinity? 155.212.242.34 (talk) 23:31, 21 February 2008 (UTC)

I had an eye test the other day and asked the optometrist. He said that it is a measure of angular resolution, so the eye chart I read was at a distance of 20 feet. The top line of the chart, the "20/400" line, would subtend at 400' the same angle as the letters in the 20/20 line do at 20'. He said the physical limit for best-possible vision is something like "20/6" or "20/8" (I forget); perhaps that is the diffraction-limited resolution?
That's all well and good. The thing I don't understand is how this measure interacts with accommodation. Assuming for the moment that ones eyes are free of astigmatism, then the primary concern is inability to focus. It looks like the eye is 23mm along the optical axis, so focusing at infinity, that's the roughly focal length looking at infinity. Focusing close, say 10cm, the focal length, according to the thin lens formula, is 18.6 mm. Taking the reciprocal of those focal length gives diopters, a range of 53.5 to 43.5 diopters — 10 diopters of accommodation. For example, unaided I can't see acutely beyond 28cm and can focus down to about 8 cm or 9 cm, corresponding (using the thin-lens formula) to a range of 47 diopters to between 54.6 diopters and 60 diopters respectively.
It seems like a measure of visual acuity only measures anything when it is outside of the person's range of accommodation. Is the assumption with the 20' denominator that most people in need of glasses are nearsighted?
PS, Please correct me if I'm misrepresenting any of this. —Ben FrantzDale (talk) 02:07, 20 May 2008 (UTC)