Snellen Results - Blurry or Clear?

Hi guys,

I’m sure this has probably been asked and answered before, but I couldn’t find it.

When checking the snellen I can read down to the 20/20 line with my norms in good natural light indoors but it is quite blurry (and possibly double vision), but even the big E at the top is a little blurry unless I do AF.

Should I be waiting until I can see the 20/20 line (or really the whole chart) “clearly” before reducing, without AF obviously, or do I just need to be able to read it even if it’s a little burry?

I’ve been at this a long time, but have had to backtrack quite a way as I believe was reducing too quickly, so don’t want to make that mistake again.

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Some people wait until they can see 20/25 before reducing.

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Yeah I can definately read 20/25, but it’s the blur that I’m interested in. Is it ok if the 20/20 (or 20/25) is blurry or does it need to be crystal clear?

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I think it is better if you can see it clearly before reducing.

I tend to agree, but the whole chart is a little blurry even the big E, but I can read the 20/20 line ok albeit a little blurry.

I’m sorry if this seems like a silly question but as I’ve had to basically restart I’m starting to question everything about EM that I thought I know already haha.

I’ve heard Jake mention before. That it doesn’t really matter when you reduce as long as you keep everything as consistent as possible. This includes the snellen line, but also the same room, same chart, same lighting conditions.

So if you reduced last time on the 20/20 bit blurry in natural indoor light. Then you could probably do that again. Thats means you’ve improved back to that point.

BUT. The danger is if you reduce on the 20/20 bit blurry natural light but LAST TIME you reduced on the 20/20 but with no blur, crystal clear. This would mean you haven’t imporved and you’ve just taken a slight step back.

Me personally. I aim for being able to read the 20/20, no active focus, indoor well lit with no natural light. Before I reduce.

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To be honest I can’t remember if it was blurry or not last time. The last time I reduced was almost a year ago…before lockdown. Had a bit of a downward spiral since then. But yeah would proababy be best to wait until the blur on the chart clears up before reducing again, just getting a little impatient haha.

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haha yeh I know the feeling.

Yeh other thing I keep in mind is just the outdoor blur challenge.
If I’m not getting any blur challenge / double vision outside then I’m more confident to reduce.

Yeah still a slight blur challenge outdoors…but not always haha. Sometimes can see really well with bugger all blur, other days (even sunny) not so great. So yeah, probably best to hold out for a little while yet.

I think I’ll wait until the snellen is really clear, like it is when I do AF on it, and will probably also wait until my centimetres are at least 30cm as -3 is where I’m going next. Don’t want to rush anything this time, doing that has cost me about a year.

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Yeh cool. sounds like a plan

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I think your question points to an important thing that many people have asked here and there in the forum, yielding quite misleading answers in some cases. The thing is: If you could see the big “E” crystal clear - then you would be able to read every line on the snellen equally as clear. The lines do not get “more blurry” as they go down. They are all equally blurry, they just get more difficult to read as the letters get smaller! The question is: how far can one read down the chart until the blur makes the letters illegible. If people say that they can read the 20/20 line but not the line beneath it cannot mean that they can read the 20/20 line crystal clear - it means they can identify the letters despite the blur.

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Yes exactly. So I guess you need the whole chart just “clear” enough to be able to read the 20/20 line. Even when I do AF and really clear the chart up, I still can’t see much beyond 20/20 (maybe a few letters further down but not much) as they are just too small. This is with a 3 metre chart anyway.

@WayneB

Thanks for characterizing your vision on the Snellen chart. I do not have a resolution for you, but have some questions:

  1. What’s your current normalized and differential?
  2. How would you characterize your close up vision?
  3. Do you have any observations on how your outdoor vision has changed in regard to peripheral vision, perception of color, perception of contrast, perception of motion etc.?
  4. How would you characterize your outdoor vision – for example, for seeing signs while driving at various speeds? For seeing leaves blowing in the wind?

I don’t need a resolution as such, this was more of a query than an actual problem.
My differentials are -1.75, norm -3.25.
Close up vision is generally really good.
Changes in outdoor vision? Not sure really. I haven’t really been taking too much notice of the things your asking about. But my distance vision can vary quite a lot from day to day, from really clear one day to quite blury the next…for no apparent reason.

Right - even when you do an eye test at the optometrist all they ask is that you be able to make out the letters, even the majority of the letters. It’s not about how clear they are

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@WayneB @Jane or anyone else: have you made observations as indicated in the table below? If so, what have your observed? And when you do a reduction of normalized, what are the values in the various columns (for example, is the second column 0 and the third infinity) and what is your differential at this time?

+------+---------------+--------------+---------------------------------------+
|      |               |              |   These two are likely to be close    |
|      |               |              +-----------------+---------------------+
| Date | Time it takes | How long the | Smallest line   | Smallest line       |
|      | for lines to  | sharp vision | that can be     | that can be         |
|      | become sharp  | lasts        | read with blur  | read with sharpness |
+------+---------------+--------------+-----------------+---------------------+
|      |               |              |                 |                     |
+------+---------------+--------------+-----------------+---------------------+

My pattern within a certain correction is blur => DV => clarity
Blur is when the line is not as black as the others above it. DV is when the line is black but the letters have ghosts. Readable if I can differentiate F from P and from E, good if I can differentiate O from C in the 20/20 line without having to wait for the clearing up (some blur or DV allowed, but no guessing about overlapping images).
I wrote about Snellen clarity here and here. Yes, even the big letter E can be fuzzy sometimes.
I usually dropped when I could immediately read FELOPZD with absolute certainty about FEOP and in DEFPOTEC I was only slightly unsure about C - slightly unsure if I can really see the gap.
At the same time I also measured clarity on number plates of parking cars, looking at them in a row on the other side of the street. If I could definitely read 5 to 7 number plates anytime, it was time to drop. And I expected 2-3 cars’ distance from the new, lower corrections.
This is for walking and using normalised, for driving I’d keep the glasses 0.25D stronger until I get to 4 to 5 cars again with the lower ones, too.

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Do you have an astigmatism? This could make things look like a blur but it is readable.

I can’t see whom you asked. If me:
I had the same prescription with the same 0.5 cyl at the same axis for decades while I had similar set up around my main work area (lights with similar brightness, always coming from the same direction). At the opto‘s recommendation the cyl was not added to my glasses and I wore normal non-toric contact lenses anyway. Then I started moving around for work and my cyl axis and strength started to change, too. I guess it adjusted to the direction of lights wherever I stopped for a month at least.
Also I think that similar to left eye right eye not adjusting to a drop at the same speed, I have this within my eyes too, and some parts get clarity easier than other parts at certain axis. I have had residual part blur or DV to clear at the last part of each reduction. Never exactly the same. My own personal Flying Dutchman coming and going :sweat_smile:

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