How clear do I actually need to see to "clear the line"

Kinda dumb question, but how clear do I need to see a line on a Snellen to say that I see it? If I can make out the letters, though they are somewhat fuzzy, is it clear enough? Or do they need to be super sharp?
I have a tiny bit of astigmatism going on that makes things a bit double-y, but I can make out the letters.

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if it’s a bit ‘doubly’ you want to keep that Rx till the doubly disappears. if you reduce while it’s still doubly you’ll be reducing too soon and if you do, sometimes you won’t make the next normal 3 to 4 month reduction and instead take 6+ months before your next reduction.

some people have been stuck for a year before they can make their next reduction because they ignored the doubly. :slight_smile:


What does Rx mean? I’m still new so I’m not sure but does it just mean your current prescription?

Well if you have doubts then maybe it is best to clear up the doubt by staying a bit longer. The rule of 3-4 months is a pretty good rule. And consistent view is a good rule. Say you look at that line and it is 20/15 but it comes in pretty good for weeks. Then maybe time to move on. My chart is a little tricky with a bunch of O Q G and □ on the 20/20 but the 20/15 was clear. But if 20/30 is the best line make sure you stick it out. I suppose the higher dioptors are easier to mistake in cm but that is also a big part of the plan. Make sure those cm are moving along to know you are ready.


So my question was about what does “pretty good” look like? Completely clear? Like I don’t need to do AF or anything. No effort whatsoever. Yes that correct?

Hi! Differing opinions on this one. Let me share mine:
A.) if I can read the letters VERY comfortably and without effort
B.) if I can do A without help of Active Focus
C.) I can do A and B consistently for more than a week

So to answer your question directly, not necessarily completely clear. (At least that’s how I measure.) However by doing that, you’re in the risk of reducing too early, that is why most people in the community would recommend to stay a bit more on the line until it’s really clear.


It can be blurry. It would be only totally clear if your edge of blur is at or farther than your Snellen chart. But in that case the result is totally unreliable (hence low myopic people should not use 3m Snellen).

So it’s ok if it’s blurry. But you should not AF on it. I think there is an “automatic” part of AF which you cannot avoid, but you should definitely not try to clear up the lines. Just look at the chart and what you can read is your line. So no guessing, no “maybe if I look a bit more I can see”, no trying for minutes to see which line you can see. Just look at the chart and what you can read at that moment is your line.


I’d say you are aiming for the top 2 versions of “aio” and for clarity close to line 3 of “focus”.
(aio shows the blur due to astigmatism / cyl with distortion depending on the axis while focus shows the blur due to sph / myopia and like most people you have a mix of them)

As others said, it should be achieved without conscious AF, without waiting time for clearing up and consistently for more than a week in the evening and in the morning, too. Down to line 20/20 on the Snellen.
@Janica’s points give a good summary for this.



If you can read the letters correctly you get credit for it on an eye exam. Usually you’ll get credit for a line if you get up to two of the letters wrong on a visual acuity test with 8 letters or more. So if they ask you to read a bunch of numbers and letters and they’re somewhat fuzzy but you can read them that “counts” for saying you have 20/40 or 20/20 vision as far as officialdom is concerned.

If the question is when should you reduce your normalized to weaker glasses, the general thinking around here is to wait until it’s nice and clear, and then wait a little more. If the 20/20 line is readable but you can see some blur on it, you’re probably still getting some blur challenge to clear. If on the other hand the 20/15 and 20/13 lines are also readable you’re probably due for a reduction.

The question for reducing is “can I still make some progress with this pair of glasses, or have I really gotten all the progress I can get without reducing further?” In general it seems to work better for people who add in an extra week or two before they make their next reduction, even after everything is already very clear and sharp. Otherwise it becomes easy to just be used to a lot of blur.


Can you elaborate on that? This idea is new to me, and I’d like to understand why it would be so.

Low myopic like under -1.00. At that point the edge of blur is too far and that makes the 3m Snellen less reliable.

I don’t mean to be dense, but don’t the smaller letters compensate for the shorter distance? In the creation of blur there are two elements, not just one: the distance and the size of the object being looked at.

I’d say in theory (and by the formula) it is the same, in practice it is not. I’m still on a journey where what used to be my close up distance is still expanding, just measured in several meters now.
I had a flat where the distance from the sofa to the kitchen cupboards was 6m and there was a door at 3m. So I put the same chart up and tried to read 20/20 on the 3m and 20/40 at 6m. For my eyes it wasn’t the same at all. A year or more later - spent in the last diopter - they are the same.


Smaller size doesn’t cause blur. The blur only depends on the distance. Of course it’s easier to perceive blur when you have more details and smaller size usually means more details. And when you has no blur (or too small amount of blur) you don’t measure your myopia anymore, you simply measure the resolution of your lens + retina system.

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Really? It certainly does for me. And isn’t it the whole premise of the Snellen chart that you get blur as the point size gets smaller?

My interest in this question isn’t just abstract. Using a 6m chart is not practical either in my apartment or in my small (walled) garden.

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No. You have constant amount of blur for the whole Snellen (well, almost constant, because the blur horizon is a sphere, while the Snellen chart is flat. But the difference is negligible at that distance). But as you go to smaller font size there is a point where the details are small enough that they are not distinguishable with that amount of blur. But you have the same amount of blur at the 20/200 line than at the 20/20.

That’s the whole point of Dyop: Snellen is not measuring resolution acuity, it’s measuring recognition acuity.


It seems that I can’t believe these lyin’ eyes!?!

Agree with all your statements on this subject David except this one:

I think the 3m Snellen is less accurate at every level, not just low myopia, because of the diopter bubble reality.
Obviously, people have to work with their space, but it is my own experience that you have to keep in mind that if you are using the chart at the shorter distance your results are going to come across more idealistic than is going to pan out in real distance settings.

Based on your posts you are relaxed enough not to be dependent on a Snellen chart for feedback.
You don’t need a chart at 6m, you just need to be aware that your clarity can always increase and that biology doesn’t follow the mathematical formula 100%. 20/20 at 3m is not the same as 20/40 at 6m.
Looking at your walled garden, the light yellow column is a good point, and the decorative motifs separating the floors on the building, too. If you keep raising your gaze higher and looking at them for a few minutes a day, e.g. while sipping a cup of coffee or tea, you’ll gradually see that what you thought was clear can be clearer and there are a lot more little details to explore. It’s an experience similar to the one when you went hiking / boating and though you were perfectly OK in norms (all looked clear), you decided to add back a bit for full clarity.

Also if you have a favourite kiosk or bar at the beach with a favourite bench, you may have some texts to look at from that position and over time you’ll gradually notice that you can see thing crystal clear, things that you didn’t even expect yourself to be able to make out.
At least this is how it works for me. E.g. for quite a while I settled with reading number plates at about 5 cars’ distance and when that was rock solid I dropped 0.25D again. So when I looked further than 5 cars I was always expecting blur but hoping to still be able to just make out the numbers and letters. As there are no more reductions from sph, I keep finding that I look at something totally unexpectantly, not even thinking about looking intentionally (as “who would be able to read something at that distance anyway?”) and then clarity hits me with joy.
Just yesterday I was standing at one end of a long platform. I was looking in the far distance trying to see if the train was coming. Not expecting clarity or anything as I was looking at hundreds of metres away. And then I realised that at the other end of the platform - which was already very far but still half way to the distance I was screening for the train - I saw the platform number crystal clear and also some safety signs next to it. It wasn’t that I was trying to read them. I wasn’t looking at them, I didn’t even register them, they literally “jumped into my face / eyes”
And the difference to a clear flash was that it wasn’t a flash only. :relaxed: