Talk:Visual acuity

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Denominator is needlessly confusing[edit]

There are only 11 lines in the eye chart. So why not 20/1-11?

-G — Preceding unsigned comment added by (talk) 01:33, 2 April 2012 (UTC)

Change's name[edit]

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

testing your own vision?[edit]

Is is possible to test your own vision at home without going to an eye doctor? Or is special equipment needed? It seems like all you need is a paper with letters of a certain size, the right amount of light and a measuring tape. Perhaps some instructions on how to determine your visual acuity at home could be added.KannD86 (talk) 14:31, 28 May 2009 (UTC)

Note that testing your distance acuity would not give you much information about the health of the eye, and nothing about the peripheral vision. —Preceding unsigned comment added by (talk) 22:04, 8 January 2011 (UTC)
You could use the Freiburg Visual Acuity Test (FrAcT) at home on your computer. Strasburger (talk) 18:45, 18 January 2014 (UTC)

Remake article[edit]

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)

Add some things...[edit]

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)

Maximum visual acuity[edit]

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 (talk) 02:31, 17 April 2008 (UTC)


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)

A lot added by now...[edit]

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)
Try and for more information about Jaeger and others, including point size equivalents (and a critique that there are not more consistent standards). Kevinbsmith (talk) 13:29, 29 December 2008 (UTC)

Maximum VA vs. average VA[edit]

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)
I'm just a lay person. I've been searching the web for statistics on human visual acuity and have found nothing. You would think an article on visual acuity would have statistics on the top 1%, top 10% bottom 10% and bottom 1%, or something like that. But all we have is 20/20 is average. (talk) 07:11, 31 March 2013 (UTC)
Is 20/20 really average??? Does anyone have a study to back that up? If so, citation needed! (talk) 07:11, 31 March 2013 (UTC)
No, 20/20 is not average. The difficulty here is that this is age dependent. Below around 45 years of age, the average is much better; above it's lower. There are graphs in the optometry literature which make this precise. A main reason for the decline with age is increasing opacity of the lens and cataract. Recently the population statistics have changed again since cataract operations have become standard. — There should be a section on age dependence. Strasburger (talk) 19:01, 18 January 2014 (UTC)


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)


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)
Well, imo they could be stated more precisely but more detail is required then. E.g., binocular acuity is much better than monocular acuity, and acuity depends heavily on luminance. Strasburger (talk) 19:07, 18 January 2014 (UTC)


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)
Diopters also don't account for age related far sightedness (presbyopia). My eyesight is 22/20, but my reading glasses are +1.75 diopters. So just right there the chart above is wrong. (I am not an expert, but I expect that diopter would only relate to visual acuity when the defect is in the curvature of the eye or a deficiency in the lens not related to flexibility. In other words where the prescription is valid at all distances.) (talk) 07:16, 31 March 2013 (UTC)
There is a basic misunderstanding here: Diopters (i.e. refraction) and acuity refer to entirely different things and are absolutely independent of each other (as said in the comment above). A shortsighted person who wears his/her –4 Diopter eye glasses will typically have 20/20 vision or better. A far sighted person of +4 Diopters will have 20/20 vision or better even without wearing his/her glasses provided things are sufficiently far away. A presbyopic person needs reading glasses, but, again, acuity will be normal once the correct glasses are used. — The top part of the table could refer to a situation where a short sighted person does not use his correction, but the bottom part is just bogus. So I am afraid the table is made up. Strasburger (talk) 19:34, 18 January 2014 (UTC)

Normal vision?[edit]

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." 23:58, 29 June 2007 (UTC)

I wear reading glasses but my vision is 22/20, so slightly better than 20/20. The problem is I'm 58 and I have age-related far sightedness (presbyopia). My vision is good, but not at the distance at which you'd hold a book. I read books at a closer distance than eye test wall charts are posted at. (talk) 07:25, 31 March 2013 (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 (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 (talk) 00:11, 28 April 2008 (UTC)
Good points. Where is the journal article reporting the study saying half the population has better than and half worse than 20/20 uncorrected vision? And where is the journal article saying that half the population has better than and half worse than 20/20 corrected vision? I just spent 30 minutes searching the web to find out, and it seems to me at this point that it is more of a religious belief, rather than a scientific fact.
And if that a citation is to an actual journal study of visual acuity is found, could we also list what the top 1%, 10%, and bottom 10% and 1% are?

Star vision test[edit]

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.) 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)

Ạẚ== 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 (talk) 23:47, 27 April 2008 (UTC)

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

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?????? (talk) 02:59, 30 November 2007 (UTC)

10/10 vision would be the same as 6/6 vision or 20/20 vision. For visual acuity of A/B, you can see at distance A what a normal person can see at distance B. — Preceding unsigned comment added by (talk) 07:29, 31 March 2013 (UTC)

Football coach?[edit]

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


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)

20/20 and all that[edit]

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? (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)
At 20 feet distance you need 0.16 Diopters accommodation to focus. That's close to nothing and therefore visual acuity measured at that distance is considered to need no accommodation (i.e. the optotype is well within the range of accommodation). Now, acuity measurement only makes sense if you wear the correct glasses. If you do, then acuity measured at distance, i.e. at 20 feet, is an overall measure of the visual system's maximum resolving power after correction. It will typically be above 20/20 or – which is the clearer way saying it – will be above 1.0. The 20 feet are really just an arbitrary number. (The international recommendation is to use the fractional notation as far as I know. Strasburger (talk) 20:14, 18 January 2014 (UTC)

Visual acuity scales[edit]

In the table of visual acuity scales, shouldn't the decimal corresponding to 20/30 and 6/9 be 0.67, rather than 0.63? -- Sakurambo 桜ん坊 12:23, 7 July 2008 (UTC)

Yes, it should. Now fixed. Isidore (talk) 19:02, 29 December 2009 (UTC)

Myopia and Hyperopia[edit]

On a foot scale, how would myopia (near-sightedness) and hyperopia (far-sightedness) be measured? Sorry for having to ask. DanMat6288 (talk) 18:18, 21 October 2008 (UTC)

As a partial answer, one could measure the nearest and farthest distance one can achieve sharp focus. The classic 20/20 vision measurement is a different way of measuring distant vision -- it tells you how poor your vision is focusing at distant objects. The correction of lenses (in diopters) is yet another measure. It tells how powerful a lens you need to focus at infinity.
That isn't a great answer, but I know where you are coming from -- I was asking questions like that a year ago and now feel confident in my understanding. Basically there are a few things that change as vision degrades. Your range of accommodation can reduce, and your focal range can shift near or far. The power of your eyes is measured in diopters, and that power changes as you adapt, but you can only adapt so much. If you can't get far stuff in focus, you can add a lens to move the diopter range of the combined eye-and-lens system to focus further out.
But yea, the easiest thing to measure at home is the range of distances at which you can focus sharply, and it's not obvious to the layperson how to convert that to diopters or x/20 vision. Maybe having those formulas on this page would help. —Ben FrantzDale (talk) 13:41, 22 October 2008 (UTC)
Sorry to disagree. (i) Near sightedness can be roughly assessed by looking at the farthest distance which gives sharp focus (the so-called far point). (ii) Far sightedness cannot be guessed from viewing distances. In fact it typically goes unnoticed by the subject. The diagnosis is by using plus lenses (and paralyze the ciliar and pupillary muscle). Uncorrected far sightedness makes itself known by headache. (iii) Near sightedness can be roughly converted to diopters: One divided by far point in meters gives Diopters (negative number). (iv) Far sighted to diopters: Get reading glasses in the supermarket. If you can see with them at distance then its more diopters than is written on the glasses. (v) There is no way of converting diopters to acuity. The two refer to different concepts and are unrelated. Strasburger (talk) 20:38, 18 January 2014 (UTC)

Where processing happens[edit]

"the sensitivity of the interpretative faculty of the brain" is an early phrase in the summary. Processing appears to happen in the retina, whence signals are propagated to thebrain not depending on just one photoreceptor, but on several. "brain" should perhaps be changed to something including more of the nervous(?) system from retina to optic and other cortex. Or removing "of the brain" and discussing later where the interpretative faculty is implemented. This is an articlet hat looks good, and is going to be useful and interesting to many people. Midgley (talk) 08:27, 14 May 2009 (UTC)

Snellen used 20 feet?[edit]

I've just edited this text for 1875:

"Snellen changed from using feet to meters (from 20/20 to 6/6 respectively or, for adherents of the decimal system, to 5 meters). Today, the 20-foot distance prevails in the United States, 6 meters prevails in Britain, 5 or 6 meters are used in continental Europe."

Would Snellen, being Dutch, have worked in feet? Also, 20 feet is 6 metres, not 5. Isidore (talk) 18:30, 29 December 2009 (UTC)

I should have checked the references already provided! says Snellen originally calibrated his charts in Parisian feet. 1875 was the date of the Metre Convention, so it seems likely to me that was the spur for Snellen's change to metres. I'm still not convinced about 5 metres being used in parts of Europe, though. I'm not a health professional, but this is the first I've heard of it. Still, I note that August Colenbrander (the author of the reference) is Dutch: I found this other paper of his interesting, too: "The Historical Evolution of Visual Acuity Measurement"
I searched Google Books today and found references to "History of Ophthalmology" by Julius Hirschberg, written in German between 1899 and 1917. Volume 10 (wow!) includes the 19th century, the Netherlands and Snellen. I wonder if this is where the 5 metre figure was first written about? I see there's an English translation in the Imperial College & Science Museum Libraries (London): -- Isidore (talk) 19:54, 30 December 2009 (UTC)

numerator / denominator[edit]

I think it would be more clear to say "the first number" and "the second number", since fractions aren't quite universal. —Preceding unsigned comment added by Sam Coskey (talkcontribs) 02:03, 3 March 2010 (UTC)

Historical definition of VA[edit]

In the History section the term VA is supposedly defined recursively with a reference to itself - this is probably incorrect.

Year Event
.. ...
1861 Franciscus Donders coined the term visual acuity to describe the “sharpness of vision” and defined it as the ratio between a subject's VA and a standard VA.
.. ...

Visual acuity testing in children—accuracy of statement...[edit]

The following paragraph was in the main text under the Visual acuity testing in children section. I've moved it here because, whilst it may well be correct, I think it would be helpful if someone who knows more than I do about visual acuity could render it less technical and edit the main page as appropriate. Thanks! talkGiler 14:41, 20 May 2010 (UTC)

The assertion regarding newborn visual acuity [saying that it is approximately 20/400] is probably a mistake or a typo. Please see page 62 (first page of Appendix C: Review of the Progression Literature) of the 1989 study, Myopia: Prevalence and Progression, done by the Committee on Vision, Commission on Behavioral and Social Sciences and Education, National Research Council: Quote, "Cook and Glasscock (1951) measured refractive errors of 500 30-hour-old infants (185 white infants, 315 black infants) by retinoscopy under atropine cycloplegia at the University fo Arkansas School of Medicine Hospital. Most frequent was hyperopia of 1.00 to 2.00 diopters (D.), with a range of -12 to +12 D. of the 1,000 eyes thus measured: 74.9 percent were hyperopic or emmetropic [normal] and 25.15 percent were myopic. Kempf et al. (1928) took retinoscopic measurements of 333 white 6- to 8- year-olds in Washington, D.C., under homatropine cycloplegia. The distribution of refractive errors ... " What is failing to be discussed is the possible latent myopic side-effects of the legislatively mandated application of neonatal eyedrops within an hour or so of birth:

Superior vision[edit]

The article says that 20/10 is "superior", i.e. you can see at 20 feet what others can only see at 10. But isn't that merely hyperopia, farsightedness?? Doesn't that mean that if you have 20/10, you see worse up close, say 1/2?--Dbjorck (talk) 09:00, 12 September 2010 (UTC)

No, not necessarily. In the past, my father had 28/20 and he doesn't suffer for any hyperopia or presbyopia. Birds, for example, generally have a superior acuity (I think, 140/20 for certain species), and non any linked problems. (sorry if I'm not clear, I have a medium level in english). Idlem (talk) 16:46, 9 July 2011 (UTC)
No, not at all. Acuity and near/far-sightedness are different concepts and are unrelated. Strasburger (talk) 20:47, 18 January 2014 (UTC)

used "lens" meaning "eyes"?[edit]

The statement "because it does not specify the nature of the problem with the lens" I think refers to the ability of all parts of the visual system, not just the crystalline lens. —Preceding unsigned comment added by (talk) 22:18, 8 January 2011 (UTC)

Denominator in the phrase 20/20[edit]

"The denominator indicates the size of the letters" I believe this statement is incorrect. How does the number 20 indicate the size of the letters? — Preceding unsigned comment added by (talk) 17:33, 18 August 2011 (UTC)

Perfect vision[edit]

This article states that "20-20 is perfect vision" in the Physiology of visual acuity section. Later, in the Normal vision section, it states that "it is inaccurate to refer to 20/20 visual acuity as 'perfect' vision". I imagine that the latter is correct and that the former should be changed, but I don't really know much on this topic so I'll leave it for somebody else to change. — Preceding unsigned comment added by (talk) 05:35, 16 February 2012 (UTC)

Denominator in the phrase 20/20[edit]

The author states "In the expression, 20/20 vision, the numerator refers to the distance in feet between the subject and the chart. The denominator indicates the size of the letters, expressed in millimeters. The denominator does not measure the height of the letters. Rather, the denominator measures the distance of the separation of the lines that make up those letters."

then goes on to state-

"At 20 feet or 6 metres, a human eye with nominal performance is able to separate lines that are one arc minute apart (equivalent to lines that are spaced 1.75 mm apart."

How does the denominator ( the number 20) in the term 20/20 represent 1.75 millimeters?

I believe the latter statement "A visual acuity of 20/20 is frequently described as meaning that a person can see detail from 20 feet (6.1 m) away the same as a person with normal eyesight would see from 20 feet." to be true. — Preceding unsigned comment added by (talk) 22:28, 1 March 2012 (UTC)

Inconsistent definition of 20/20 vision[edit]

There is something inconsistent in the introduction. Paragraph 6 says "The letters in the lowest line in the Snellen chart are composed of lines that are separated by a visual angle of one arc minute". In the figure of the Snellen chart, the lowest line is three lines below the 20/20 line. So if you can discern lines separated by one arc minute you are seeing much better than 20/20.

The next paragraph says " a human eye with nominal performance is able to separate lines that are one arc minute apart" so, nominal must be a lot better than 20/20. Then the next sentence says "A vision of 20/20 is considered nominal".

So, either normal human acuity can resolve 1 arc minute and the lowest line on the Snellen chart has features much less than 1 arc minute, or the lowest line on the Snellen chart has 1 arc minute features and 20/20 human has much less resolution than 1 arc minute. Constant314 (talk) 02:15, 11 December 2012 (UTC)

Visual acuity in animals[edit]

How can the visual acuity in hawks be 20/2? Considering 20/20 is 60 seconds of arc and implies a 2.3mm diffraction limited aperture using the Rayleigh criterion then a 20/2 acuity implies a diffraction-limited aperture of around 23mm, for a 6 seconds of arc resolution. That's far bigger than even owl's eyes... impossible! Even yesterday I was looking at an eagle and her eyes don't have a much bigger pupil in the sun than ours, which are already near diffraction-limited. And her eyes are relatively small also, and therefore her pupil can't grow above 6 or 7mm at most, limiting acuity at best to 20/7 or so. — Preceding unsigned comment added by Rnbc (talkcontribs) 21:02, 21 July 2013 (UTC)

Raptors do have other adaptations within their eyes that are absent on humans, such as strategically placed oil droplets within their eyes that increase the contrast. Also I don't know where you are getting the 20/2 visual acuity for hawks. They don't really get much better than 20/7.5, as you predicted. Humans have ‘foveal vision’ (acute only in the center), while raptors, on the other hand, have a high proportion of cone cells spread over the entire retina. This provides raptors with an all-around visual awareness far superior to that of humans. Raptors are also sensitive to a larger color spectrum than humans are. They have two types of cone cells (we have only one), four or five color-sensitive pigments (we have just three), and oil droplets which enhance contrast in different parts of the field of vision. — Preceding unsigned comment added by (talk) 08:23, 19 February 2014 (UTC)
That's very interesting and some of it might go in the article imo (in a separate section). The "20/2" appears in a somewhat dubious reference in the section "Expression". Strasburger (talk) 10:42, 28 May 2014 (UTC)
The reference to 20/2 vision has now been removed, so this comment in the talk section is now historical only. Rnbc (talk) 13:20, 29 August 2014 (UTC)


Someone has changed a bunch of word to 'megaman'...? a quick look at the history shows the first instance is 'brain' > 'Megaman' — Preceding unsigned comment added by (talk) 16:14, 31 October 2013 (UTC)

Move in out motion produces pulse producing focusing problems. Focus in out to produce strength. XXX — Preceding unsigned comment added by (talk) 01:35, 30 January 2014 (UTC)

Possible Typographical Errors[edit]

I am not an expert in this field, but while reading through the article the following caught my eye:

RE: Section 5.1, Legal Definitions, near the bottom of the section it gives this example of notation used in the documentation of visual acuity:

"So, distant visual acuity of 6/10 and 6/8 with pinhole in the right eye will be: DscOD 6/20 PH 6/8. Distant visual acuity of count fingers and 6/17 with pinhole in the left eye will be: DscOS CF PH 16/17."

Is it correct to write: DscOD 6/20 PH 6/8 -- why is it not 6/10? and the second: DscOS CF PH 16/17 -- why is it not 6/17?

If these notations are not a typo, and are correct as written, then it would seem an entry discussing how these numbers are derived from the raw data should be included.

Static1st (talk) 13:39, 11 August 2015 (UTC)

Why is this entry being questioned?[edit]

Just want an answer. — Preceding unsigned comment added by (talk) 05:22, 19 November 2015 (UTC)

Hi. If you refer to the "multiple issues" warning, that was inserted quite some time ago (before I came here) and much of it has probably been resolved. The section "Physiology" still needs a brush-up (I did only the first paragraph). Whether it is still confusing overall I cannot say. Strasburger (talk) 15:18, 19 November 2015 (UTC)
I have now cleaned up the section "Physiology" and removed the warning. Strasburger (talk) 13:44, 9 May 2016 (UTC)

Too technical[edit]

This article is so technical and full of jargon that an educated laymen cannot understand it. I have a degree in Computer Science from Cambridge University and am relatively technical in my general knowledge. Yet this article is beyond my ability to understand. This suggests most of the population will be unable to understand it. This article needs considerable clarification and explanation of the terms used.

I have changed three sentences in the introduction, so at least the introduction should now (hopefully?) be straightforward to read. I might be the wrong person to tell, though, so please be more specific in where you think it needs being simpler. Strasburger (talk) 22:27, 29 August 2016 (UTC)