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.

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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.