Talk:Snellen chart

Not all eye charts are Snellen charts

Although Snellen charts are eye charts, not all eye charts are Snellen charts (see recent additions of Landolt C and Lea test). I'm wondering if anyone else thinks that Eye chart should NOT redirect to this article. Edwardian 06:44, 15 September 2005 (UTC)

• That's a good thought. Snellen chart was, for so long, the only eye chart article we had, so a redirect made sense. Now, though, I think "eye chart" should probably be a disambig page for the snellen, landolt C, and lea tests. Joyous (talk) 11:01, 15 September 2005 (UTC)

• Good idea. The first line of the Snellen chart article should also be adjusted. Dontaskme 19:47, 15 September 2005 (UTC)

I've re-created Eye chart with mention of the above charts. Much of the information on Snellen chart (i.e. "20/20 Vision", "Variations") should probably be moved, too. Are you guys OK with that? By the way, the "Big E" on my Snellen chart is a 20/200 letter, but I also have a projection chart (which I don't think it is technically a Snellen chart) with a 20/400 "Big E". Edwardian 21:02, 15 September 2005 (UTC)

• Yes, I think everything that is not specific to the Snellen chart should be moved.

In Hungary it seems that every optometrist uses an eye chart somewhat unlike this one (but always the same one). It's one with numbers only, no letters. The top row which has the largest numbers reads 42. Below that, there are two digits in the first few rows, and three two digit numbers in the lower rows: there's a column of numbers divided by a bar on each side, but the three numbers in each row has the same side. On the bottom there's a special row with several numbers of different sizes (but smaller ones than above). There's a thin red line in the chart but no green one. There are also two similarly looking charts I occasionally see, one has E shapes rotated in four directions, the other has letters, but I belive they're not the same as the chart show here, as they're similar in alignment to what I've described here in that all symbols appear in twos.

I wonder if Wikipedia has information on these charts. – b_jonas 09:38, 1 June 2006 (UTC)

Tumbling 'E' charts

Could someone post a photo of this in the article? It's the tumbling 'E' version of the chart (consisting only of rotated letter E's).

http://www.independentliving.com/images/657834.jpg

Legal definitions

These need the jurisdiction indicated. I suspect it is not the same in all countries. In the UK the registration as partially sighted, or blind, depends upon a consultant Ophthalmologist's certification. Midgley (talk) 08:21, 14 May 2009 (UTC)

Creating Snellen charts

Would it be possible to have computer generated Snellen charts/selecting from several options for each line? This would minimise the putative effects of memorising the charts. —Preceding unsigned comment added by 83.104.132.41 (talk) 09:28, 4 August 2009 (UTC)

Image Denominators

In the current image for this article, are the denominators for the last three lines: 15, 10, 8? I'm guessing 8, rather than 5, since 8 would be considered the physical limit, but this could be faulty reasoning on my part. Is there a reason to not include the value of these three lines in the svg image? It would seem that if one were to include the three lines for the image then one would also include their measures. — al-Shimoni (talk) 06:11, 28 December 2010 (UTC)

I put the figures into my calculator. The SVG rendered on the screen the right size making measuring faster. And i see the conversion is linear. Line 9 is 20/15, line 10 is 20/13 and line 11 is 20/10 (at least that is what i think these are supposed to be, its actually a little lower, like 9.5 for eleven. 20/20 is right though, so maybe they guessed the rest of it). What i wonder is why they converted 3.5in to 88.7mm instead of 88.9mm. The factor is 0.0175 from inches. Charlieb000 (talk) 22:50, 4 April 2013 (UTC)

Sloan Letters

In this article the 10 Sloan Letters used in Snellen charts are given as C, D, E, F, L, N, O, P, T and Z, but on the 'Sloan Letters' page these are stated to be C, D, H, K, N, O, R, S, V and Z. Could someone please clarify? — Preceding unsigned comment added by 86.168.213.81 (talk) 13:50, 26 August 2011 (UTC)

According to this paper by Sloan, L. L. (1959). "New test charts for the measurement of visual acuity at far and near distances." American Journal of Ophthalmology 48: 807-813. The sloan letters are made up of equally legible letters and are "Z,N,H,R,V,K,D,C,O,S" — Preceding unsigned comment added by 129.78.32.22 (talk) 04:26, 26 May 2012 (UTC)

"6/6"(m) or "20/20"(ft) vision

The current calculations of optotype sizes are incorrect. If the height of the letter subtends an angle of 5 minutes of arc as required by Dr Snellen, then rounded to two decimal places the 6/60 letter would be 8.73 mm tall (2 x 6000 x tan(5/2 minutes)), not 8.86mm as in the article. The incorrect value of 8.86mm is derived from a the reference [5] 20/20 Calculation, Dr. Craig Blackwell, MD http://www.blackwelleyesight.com/eye-math/2020-letter/ which is meant as a rough calculation to determine resolution of the retina, and uses simplified and therefore inexact trigonometrical calculations to arrive at this figure. — Preceding unsigned comment added by Zzjlamb (talk • contribs) 12:06, 10 December 2017 (UTC)

Can I add infographic to snellen chart or visual acuity

If you need a link, the infographic is here: https://en.wikipedia.org/wiki/File:Single_letter_relative_sizes_visual_acuity_measurement.jpg PG D'Arcy (talk) 06:46, 23 July 2018 (UTC)

Coloured Bands

It would be helpful if the article could explain the significance of the red and green bands on the chart. HappyDog (talk) 11:28, 12 November 2024 (UTC)

Confused by distances...

"If this is the smallest line a person can read, the person's acuity is "6/12" ("20/40"), meaning that this person needs to approach to a distance of 6 metres (20 ft) to read letters that a person with normal acuity could read at 20 feet."

This seems wrong - the first "6 metres" should surely be some distance less than 6 metres.

And, by the way, the second "20 feet" should read "6 metres (20 ft)" Herbgold (talk) 11:02, 2 August 2025 (UTC)

Delete Reference 9 and related sentence

I'd like to delete the sentence "Another calculation for United States clinics using 20-foot chart distances (slightly more than 6 m), and using a 17 mm model eye for calculations, and a letter which subtends 5 minutes of arc, gives a vertical height of the 20/20 letter to be 8.75 mm." and the associated Reference 9. They contain errors and add no value to the preceding text.

The article referenced supposedly calculates the required letter height for a viewing distance of 20ft. However the answer of 8.75mm is actually for 6m viewing distance. It should therefore be the same as the figure of 8.73mm already stated. It differs only because of rounding error in the calculation. The eyeball diameter of 17mm is also irrelevant to this calculation.

So this sentence and the reference tell us nothing new. Is it OK to delete? Tenbob2 (talk) 05:07, 12 January 2026 (UTC)