# Thread: Diopters to Visual Acuity

1. ## Diopters to Visual Acuity

Hello everyone!

I was wondering if someone could post a table of diopter power correlated to visual acuity (20/20, 20/100, 20/600, etc). Please post for PLUS power lenses, I will post one below I found online, it is for MINUS power lenses.

I understand that these are only approximations, and that's just fine.
My glasses are +11.00 OU, single vision and no astig. I know I'm off the charts, but I'm curions to learn my VA, unaided, given my prescription.

I also read that the chart for MINUS is not equivalent to a PLUS power. That is, if a person wearing a -5.00 has unaided VA of 20/500, this does not mean
that someone wearing a +5.00 will have unaided VA of 20/500 as well.

Is there a formula to estimate VA for PLUS power, given the diopter used?
Please post a chart like the one below, but for PLUS rx's.

Tnx

Refractive Error & Visual Acuity
Refractive Error
Myopia in Diopters
Approximage Unaided
Visual Acuity
.50 D 20/50
1.00 D 20/100
2.00 D 20/200
3.00 D 20/300
4.00 D 20/400
5.00 D 20/500
6.00 D 20/600
7.00 D 20/700
8.00 D 20/800
9.00 D 20/900
10.00 D 20/1000

• These approximations apply to nearsighted (myopia) patients wearing glasses.

2. Well, my prescription is about a -2.50 and I see about 20/100 without correction.

3. To find your VA without a low vision acuity chart put up the 20/400 E on the chart and see if you can see it at 20 feet. If you cannot, start walking toward the chart. If you can see the E at 10 feet you have 20/800 unaided visual acuity. If you see it between 20 feet and 10 feet you have around 20/600 vision.( Could be done on any distance as long as your projectochart is calibrated properly.
Unaided acuities of hyperopes vary widely due to the accommadation of the patient up to age 55 or so. After that it is more predictible but don't know the exact correlation. But it is much less that myopes. After 35 years of practicing one gets a feel for unaided acuities but is still surprised occasionally by how good or how poor a hyperope's acuity is-and also how they don't care!!

4. hi walleye,

what do u mean by...

"still surprised occasionally by how good or how poor a hyperope's acuity is-and also how they don't care!!"

i have like zero (0) accommodation, i guess it is due to the power of my +11.00 prescription, but i cannot manage to squint/accommodate to see not even bit better. and i'm only 31 years old.

when you say that:

"...but don't know the exact correlation. But it is much less that myopes."

do you mean that someone with a -11.00 prescription will have worse unaided VA than someone who uses +11.00 ??

thanks for taking the time to reply.

5. Some hyperopes come in with say 20/60 unaided acuity and say they never wear glasses to drive and don't want to even though I've prescribed them bifocals. They only wear glasses to read. And a myope will come in with 20/25 unaided acuity and complain of distance blur and will willingly wear an Rx full time!!

When you get up into the 11.00 diopter range both hyperope and myope acuities will be very bad. But I would say the myope will be worse.

But down into the say + or - 3.00 range a 3 dioper myope might have an unaided acuity of 20/300-20/400 but a 3 diopter hyperope may have and acuity of 20/100. The bottom line to your question is that the unaided acuity of myopes is more predicitible than that of hyperopes.

6. Originally Posted by eyedoc
Hello everyone!

I was wondering if someone could post a table of diopter power correlated to visual acuity (20/20, 20/100, 20/600, etc). Please post for PLUS power lenses, I will post one below I found online, it is for MINUS power lenses.

I understand that these are only approximations, and that's just fine.
My glasses are +11.00 OU, single vision and no astig. I know I'm off the charts, but I'm curions to learn my VA, unaided, given my prescription.

I also read that the chart for MINUS is not equivalent to a PLUS power. That is, if a person wearing a -5.00 has unaided VA of 20/500, this does not mean
that someone wearing a +5.00 will have unaided VA of 20/500 as well.

Is there a formula to estimate VA for PLUS power, given the diopter used?
Please post a chart like the one below, but for PLUS rx's.

Tnx

Refractive Error & Visual Acuity
Refractive Error
Myopia in Diopters
Approximage Unaided
Visual Acuity

.50 D 20/50
1.00 D 20/100
2.00 D 20/200
3.00 D 20/300
4.00 D 20/400
5.00 D 20/500
6.00 D 20/600
7.00 D 20/700
8.00 D 20/800
9.00 D 20/900
10.00 D 20/1000

• These approximations apply to nearsighted (myopia) patients wearing glasses.

don't waste time on acuity/power estimation,half of time it will get you wrong estimation.

7. What difference does it make, if you can see well with your glasses? Unless of course you are trying to get into the Air Force as a pilot?

8. ## Egger's Chart Logic

Do some research on the above subject and you will find that for every line above 20/20 towards the lower end of the Snellen Chart, you will be approximately 0.25D away from emmetropia. So if you saw 20/40 your ametropia would be approximately 0.75D. As we move up it increases to 0.50D per line. An example would be 20/200 and the ametropia will be approximately 3.50 to 4.00D. This information can be found in a number of texts, including Borish. It does not indicate hyperopia or myopia. In the early days of refraction all testing was done utilizing subjective techniques To test for ametropia a + lens was initially employed based roughly on the line on the Snellen Chart read by the patient. If it improved the acuity, then by golly we had a hyperope. If not, then we went in the other direction and refined from there. The process is interesting and I encourage you to look further to get additional clarification. Keep in mind you will have many indicate that they see x with whatever Rx.......the eye is organic in nature and not a static instrument so these are estimates only.

9. ## diopters vs. 20/20

This topic comes again quite often and in many message boards. There are many factors determining your UCVA and pescription, too tired to list them all. Hyperopia is accomodated so they can use a cycoplegic refraction for that. The manifast refraction only reveals hyperopia not accomodated. An example is this 19 year old lady who was +6 diopters, she could accomodate +4 diopters so her manifast was +2 and her distance accuracy was 20/70 but her vision was more and more blurry the nearer she got. She would still be 20/70 with -2 myopia but her near vision would be perfect at 20" or half meter. Any closer depends how much she can accomodate and any further will gradually blur. The below are what youd see with the following diopters of myopia without astigmastim.

-.5 diopters of myopia is so little, its generally a nonissue that warrants no attention. It results in the loss of one line. 20/25 instead of 20/20, 20/30 instead of 20/25, etc.

-1 diopters results in half UCVA. You may be 20/40 correctable to 20/20 with glasses. I was 20/50 corrected to 20/25 with -1 glasses back when I was 12.

-2 diopters typically results in the neighboor of 20/100 vision but this is largely dependant on your BCVA. It can be better than 20/50 or worse than 20/200. Almost everyone can see the 20/200 easily and many can still make out the 20/100 with some effort. I fall in between at 20/150 with a -2 diopter undercorrection.

-3 diopters results in 20/200 for most people. There are a few who can make out 20/100 but they have very good BCVA. Those with BCVA's below 20/25 may not be able to see 20/200. Almost everyone can see the 20/300 quite easily though.

-4 diopters results in 20/300 for most people. Some can still discern 20/200 while others cant quite see 20/300.

-5 diopters will result in a blurry 20/400 for many. This is my pescription and I tested myself at 20/500.

summary:

-1 20/40
-2 20/100
-3 20/200
-4 20/300
-5 20/400 or worse.

20/400 is the largest E on many eyecharts. Past that, many consider it CF or count finger vision. My CF is 10'

10. Originally Posted by chip anderson
What difference does it make, if you can see well with your glasses? Unless of course you are trying to get into the Air Force as a pilot?
chip,
knowledge - or estimate- of the answer to my question will not make any difference. just a bit to satisfy my curious appetite and thirst for knowledge.
:idea: :idea: :idea: :idea: :idea: :idea: :idea: :idea: :idea:

11. Based upon various clinical studies, the visual acuity can be predicted from an absolute refractive error using the formula:

D = 10^(E / 2 + 1.25)

where D is the Snellen denominator in feet and E is the refractive error in diopters.

For instance, given a refractive error of 0.25 D,

D = 10^(0.25 / 2 + 1.25) = 10^1.375 = 23.7

Or, for a refractive error of 0.25 D, the visual acuity is roughly 20/25.

Of course, as mentioned earlier, a hyperope can compensate for some degree of refractive error, depending upon his or her reserve of accommodation (though this could put strain on the oculomotor system).

The size of the pupil, size of the object, and contrast of the object are just a few of the factors that can significantly impact visual acuity for a given refractive error (assuming that vision is otherwise healthy and normal).

12. This forumula would make a -1.5 exactly 20/100, a -3 20/1000 and a -5.5 20/10000! Either im doing the math wrong or the forumla only works for very low amounts of myopia. I have come with my own formula and testing it with plus lenses to simulate more myopia, it appears to work with high accuracy. The formula of mine starts at -2 diopters. a 50%(1.5 times) increase in diopters results in 50%(half) visual accuracy. If someone whos -2 is seeing 20/80 and his eyes get worse to -3 or he wears +1 glasses his accuracy would drop to 20/160. -4.5 diopters would then result in 20/320.

13. Originally Posted by Myoptic
Either im doing the math wrong or the forumla only works for very low amounts of myopia
Yes, this formula is a "best fit" model of measured visual acuity versus power error for a population of subjects. The study probably stopped around 3.00 or 4.00 D, so the formula will most likely break down beyond that. I probably should have made note of this, though judging refractive error from visual acuity beyond 3.00 D isn't really practical anyway, since few charts have lines above 20/200.

Originally Posted by Myoptic
If someone whos -2 is seeing 20/80 and his eyes get worse to -3 or he wears +1 glasses his accuracy would drop to 20/160. -4.5 diopters would then result in 20/320
Keep in mind that his uncorrected acuity with a -2.00 D would be closer to 20/200, and that an additional 1.00 D of error would represent 50% more blur.

14. Well, my prescription is about a -2.50 and I see about 20/100 without correction. This is what happylady(see above post) sees. I would think -2 is in the 20/70 to 20/100 range. In my vision book, this guy was seeing 20/70 with -2.5 glasses which correct to an amazing 20/15! Low myopia is less than -3 diopters and most people see 20/100 or better with a low amount of myopia. Of course as ive said, what your BCVA is affects your UCVA. I am not gonna see 20/100 with -2.5 diopters since my BCVA isnt 20/20. I would be between 20/100 and 20/200 and yes ive tested this out already with my -2.5 glasses I use for near work.

15. Nevertheless, in this particular controlled study under carefully chosen conditions, a typical observer demonstrated a visual acuity of around 20/300 with 2.50 D of error. Depending upon the ambient lighting, letter type, chart contrast, and several other optical and physiological factors (including your normal corrected acuity), you may do better or worse. Other charts based on different test criteria, for instance, may show an improved rating for 2.50 D of error.

16. Lots of good information for the trivial pursuit party and God knows we see patient's every day that want's to know "what's my vision."

But this takes in I guess, average macular and internal development. We have all seen the patient that sees 20/10 or better (with and without correction) and wonder what did we do better for this one that we are not doing for the others.
And we see a number of people who can't see 20/20 although we don't see anything wrong. Lots of stuff like optical cap placement, macular development, media clarity, surface quality of the cornea and various liquids in and on the eye, lid tension, visual axis alignment, mental development, optic nerve condition and development, brain connections, etc.. are in this system. So such charts are guesstimates.

I have often said that 20/20 means: Average acuity of British sharpshooters in the Crimean war as well as Hemholtz could measure.

Or as an ophthalmologist friend puts it: " You can't have 20/20 with a 20/200 brain.

Chip:cheers:

17. Originally Posted by Darryl Meister
Nevertheless, in this particular controlled study under carefully chosen conditions, a typical observer demonstrated a visual acuity of around 20/300 with 2.50 D of error. Depending upon the ambient lighting, letter type, chart contrast, and several other optical and physiological factors (including your normal corrected acuity), you may do better or worse. Other charts based on different test criteria, for instance, may show an improved rating for 2.50 D of error.
Another factor is how good you are at interpreting the blurry images on the wall chart. Like I said before I can see 20/100 with a -2.50 but it certainly isn't clear. I can actually make out the 20/80 line but it is extremely blurry.

Am I actually seeing the same thing on the wall chart as another person that wears a -2.50 and is 20/200 but am just better at interpreting it?

I do correct to 20/15.

18. they didnt mention how much astigmastim the -2.5d observer had or what his corrected vision was such as 20/30, 20/40, 20/50? The eyechart should be well illuminated and the room not overly bright or pitch black. If you use a proper standardalized snellen, there shouldnt be any major variance of the letters. I can easily read the 20/300 letter(s) with an undercorrection that gives me a -2.5d error. Even the 20/200 isnt much effort.

"the patient that sees 20/10 or better (with and without correction)"

how small do the letters go? If 20/10 is the bottom line, how does one know if hes better than 20/10? 20/10 is unusual, period.

"And we see a number of people who can't see 20/20 although we don't see anything wrong."

No one in my family can see 20/20 BCVA. I know alot of people not correctable to 20/20, even compenstating for spectacle minification. The online doctors think there may be something wrong. To my knowlege, I have no occular pathalogies. High order abberations and irregular astigmastim are to blame accroding to my wavefront topographies.

"Another factor is how good you are at interpreting the blurry images on the wall chart."

There is only so much blur that can be interpreted. Take my -5 for example, theres no way im gonna see 20/200 or even 20/300. I couldnt even tell you if letters even existed let alone call them out.

"Am I actually seeing the same thing on the wall chart as another person that wears a -2.50 and is 20/200 but am just better at interpreting it?"

Youd be able to easily see the 20/200 line with absolute confidence, no interpretation needed. The 20/200 line for me with -2.5d by wearing weaker glasses is certainly not clear and the 20/150 very blurry. No amount of interpretation will help me see something thats too blurry to even exist. A better indicator is have the person rate how blurry or hard to see a particular line is. If both people rate the line as very blurry and one person cant quite make it out, the other person either interprets better or sees the line a bit less blurry. However if one rates the line as clear or slightly blurry and the other as quite blurry then thats your difference. Your BCVA of 20/15 is superior to my 20/30. Glasses minify so our true BCVA compenstating for minification is 20/27 for me, 20/14 for you. 20/27 with contacts or 20/30 with glasses are equal, the letters are the same size either way. I get much more blurrying for the same diopters as you get because I have other factors that contribute to blur such as high order abberations and irregular astigmastim while you have very little in the way except pure myopia.

19. Originally Posted by chip anderson
Or as an ophthalmologist friend puts it: " You can't have 20/20 with a 20/200 brain.

Chip:cheers:
I love it !! ;)

20. This is the time to ask something I've wondered about - if I go for an eye test I know I can read the top letter, but the next one down is quite blurry. Should I try my best and guess it if not, or is the optician just wanting to know if I can see that line clearly?

Or does the fact that they know my prescription anyway influence what they'll do as a result? They probably know what I'm seeing anyway don't they?

21. Don't Guess, they want to know what you can see, not what you might be able to figure out with 10 min. of squinting and moving around. Yes, they may take the knowledge of your previous prescription into account. Nothing drives a refractionist more crazy that when asked what's the lowest line you can see than to have the patient respond: "Clearly?" He wants to know what you can read without a lot of effort, but it also drives us nuts when a patient reads line 6 and we ask what's the next one and they read it and the next two without hesitation. Just give a straight prompt answer.

Chip

22. when I had my eye exam and the opto. was finding my BCVA using various minus lenses. I think he was trying to refract me to 20/20 which is standard procedure and he kept saying "is one or is two" better and kept flipping the lenses. At the end he said alot of people dont see 20/20. Its the shape of your eye that allows some people to see better than others. Cornea, lens, retina, the whole optical network. If I can not read a line of letters within 3 seconds, I just say I cant see it. I looked at the 20/25 line for 10 seconds and said "I cant see 20/20" and he said thats the 20/25 line! Just do your best, guess if you have to. So I went ahead and got half correct. I guess I could consider my BCVA 20/30+ perhaps intacs or wavefront lasik can improve my BCVA

23. and nothing drives a lab manager more crazy than when the doc has to change the script a quarter diopter on one eye and 5 degrees on the other because the patient doesn't know what's clear or not. multiply this by about 3 or 4 and you get a normal day in the life... worse when our backup O.D. is in... I don't know who guesses more, the doc or the patients.

24. I just say "same" if both look equally clear or I just choose one. The optometrist sees that im choosing the -5 lense and the -5.25 lense half the time then he knows he has reached my BCVA pescription. I hope he does give me the lower one, id rather not be +.25 hyperopic!

25. Anyone else know how well they see and whats your pescription? What do you see without glasses? with? We are just curious and also this will give others who read this thread an idea how well they see

me: im -5 and see 20/500 without glasses, 20/30 with.
my brother is -1.25 and sees 20/60 without, 20/25+ with.
My mom is -8 and sees 20/900 without, 20/30 with.
My sister is -3.5 and sees 20/250 without, 20/25+ with.

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