What Does 20/200 Eyesight Mean?

20/200 means you have to stand at 20 feet to read what a person with normal eyesight reads at 200 feet. The top number is your testing distance, the bottom number is the distance at which a standard eye resolves that same line. A bigger bottom number means less detail resolved.

What Does 20/70 Eyesight Mean?

20/70 means you read at 20 feet what a normal eye reads at 70 feet. It sits between mild reduction and the low-vision range, and in most places it is around the threshold where an unrestricted driving licence becomes a problem.

Is 20/200 The Same As Legally Blind?

Only when it is your best corrected vision. In the United States, legal blindness is 20/200 or worse in the better eye, with correction, or a visual field of 20 degrees or less. Uncorrected 20/200 is simply a strong prescription. Most people who measure 20/200 without glasses are nowhere near legally blind, because a lens brings them to 20/20. This distinction is the single most common misreading of the number, and it frightens a lot of people unnecessarily.

Reading the numbers themselves is covered on its own page: how to read your eye prescription.

Why Does Your Snellen Number Change During The Day?

A Snellen result is not a fixed property of your eye. It is a measurement taken under one set of conditions, and it moves with light, fatigue and strain.

There is a clean example further down this page. A reader measuring his own eyesight at a fixed -2.75 correction recorded, on the same day, with the same eyes:

  • Morning, natural light: 20/30 right, 20/50 left, 20/25 both eyes
  • Night, room light: 20/70 right, 20/200 left, 20/70 both eyes

Same person, same lenses, same day. The left eye reads 20/50 in the morning and 20/200 at night. Whether that eye is “20/200” depends entirely on when somebody pointed a chart at it.

This matters for two reasons. One, a single clinic measurement taken in a dim exam room is a snapshot, not a verdict. Two, if your number moves that much with light and fatigue, the number is not describing a fixed defect in your eye.

The rest of this page is the original measurement discussion the numbers above came from.

The support forum is a gold mine of insights from participants.

For anyone working on their own eyesight, as well as casual readers considering improving their vision, I highly recommend some browsing there.  It also makes it quite easy for me to get inspirations for topics here in the blog.  Let’s look at some recent dialog:

Ziju writes:

My snellen results with the -2.75 are OD/OS/Both eyes:
Morning(natural light): 20/30, 20/50, 20/25
Night(room light): 20/70, 20/200, 20/70

My centimeter measurement with -2.75 is OD/OS: 55cm/47cm at night and 72.5cm/55cm in the morning.

I’m not quite sure about my centimeter results as I was struggling a little with the edge of blur. There was a large range of distances between fully sharpness and a bit of blur and thus I really can’t tell exactly where the blur starts. I don’t know if it is because the -2.75 may have astigmatism correction that differs from my current values. Moreover, when I was staring at the screen looking for edge of blur, the letters actually changed between blur and sharpness through time (when I was not moving).”

***

I put everyone through this exercise.  Measure!

Whether eye exercises do anything at all, against the evidence, now has one page: do eye exercises work?

Does Ziju have a pretty good idea about different lighting conditions, and how the optometrist prescription is much too strong for 90% of daily use?

I think so!

And there is also this interesting tidbit:  “Moreover, when I was staring at the screen looking for edge of blur, the letters actually changed between blur and sharpness through time (when I was not moving).”

Active focus!  It’s amazing what happens, when we learn how to challenge our eyes.  Blur turns into sharpness, and back again.  Do we really want to eliminate this with strong prescriptions?  Of course not!  We want this source of stimulus, we want to challenge our eyes to give us more focus, with progressively less prescription.

There is a whole lot more interesting things in the thread, here:  https://frauenfeldclinic.com/myopia-forums/topic/suggest-for-close-up-work-glasses/

When I catch up on the forum with a bit of time, I often write almost blog-length explanations, such as this one:

The first differential prescription is always a guess! It’s difficult to really know how the eyes will respond to stimulus and less strain in the short term.

Aside from the inconvenience of expense, figuring out the prescription, and getting it, this is a truly excellent exercise. Doing the measurements, observing your left vs. right eye, and changes with lighting conditions and strain is letting you get to know your eyesight. Along with that, you get to look at prescriptions more critically, from a “how much do I really need for this task” perspective.

I hope you are getting a positive experience from this! 

Is the distance you get with the -1.00 a bit low for being ergonomically convenient?

For the normalized (distance prescription), giving your right eye a 0.25 diopter bump will give it a better chance to contribute to your bifocal vision properly. It would still be a challenging prescription (we talk about peak prescription in the program, for which it would be excellent). Going up 0.25 and 0.50 would make life a bit easier – it’s nice to get somewhat close to 20/40 or 20/35 with some active focus.

Diopters themselves, what the number means and how to track your own, now have one page: diopters, explained.

Remember, it’s all about blur horizon. Your eyes have to be able to achieve clear focus for distances you use primarily – though it’s perfectly ok for this to take effort. So if you are outside and everything is quite blurry, it’s neither fun, nor productive. You can still work at relatively short distances for pulling focus (a topic we discuss later, after we cover all the close-up subjects), which technically is just as well for rehab. But in a practical sense, it’s often more pleasing to get more distance before that blur horizon.”

***

For Sofya’s original question and the whole thread, visit here:  https://frauenfeldclinic.com/myopia-forums/topic/prescription-for-close-up-work/

Get to know your eyes.   That is the alternative I offer, to the magic show and one-size-fits-all prescriptions you get at the optometrist.  I know this can feel daunting (though it should also be exciting) at first, but that’s why I’m here to support you in the forum, and through these articles.

Get out there and enjoy some healthy eyesight today!

 

Also worth reading

Related: 20/50 Vision: What It Means And Whether You Can Fix It · – 0.50 eye prescription how bad is that, explained · One Amazing Trick For Instant 20/20 Vision (Eye Exercise)


Related improvement reports

See how these fit the wider evidence: Are There Verified Case Reports Of Myopia Improvement Without Surgery?.

20/200 And 20/70 Eyesight: Frequently Asked Questions

What does 20/200 vision mean?
It means you must be 20 feet away to read what a person with normal eyesight reads at 200 feet.

Is 20/200 vision legally blind?
Only if it is your best corrected vision. In the United States legal blindness is 20/200 or worse in the better eye while wearing correction. Uncorrected 20/200 that glasses bring to 20/20 is not legal blindness.

What does 20/70 vision mean?
You read at 20 feet what a normal eye reads at 70 feet. It generally falls near the limit for an unrestricted driving licence.

Can your Snellen measurement change during the day?
Yes, and substantially. One reader recorded 20/50 in the left eye in morning natural light and 20/200 in the same eye at night in room light, with the same corrective lenses.

What prescription is 20/200?
There is no fixed conversion. Snellen acuity measures resolved detail, diopters measure lens power, and the relationship differs between people and with lighting conditions.

Is 20/70 or 20/200 worse?
20/200 is worse. The larger the second number, the less detail is being resolved at the test distance.

Related reading: What do the numbers on your eye prescription mean?

See more documented cases in the EndMyopia Case Report Registry.