# Optical Forums > General Optics and Eyecare Discussion Forum >  Diopters to Visual Acuity

## 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  :Nerd:  




*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.

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## Happylady

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

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## walleye

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!!

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## eyedoc

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.

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## walleye

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.

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## Graduate

> 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.
> ...


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

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## 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?

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## wmcdonald

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.

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## Myoptic33

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'

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## eyedoc

> 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:

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## Darryl Meister

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).

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## Myoptic33

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.

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## Darryl Meister

> 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.




> 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.

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## Myoptic33

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.

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## 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.

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## chip anderson

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:

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## Happylady

> 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.

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## Myoptic33

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.

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## GOS_Queen

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


I love it !!  ;)

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## Curious

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?

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## chip anderson

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

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## Myoptic33

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

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## eromitlab

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.

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## Myoptic33

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!

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## Myoptic33

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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## Curious

What is the 20/? calculation used for? I'm -2.75, what am in the the 20/scale and how does that help me understand my visual requirements?

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## Myoptic33

> What is the 20/? calculation used for? I'm -2.75, what am in the the 20/scale and how does that help me understand my visual requirements?



in a nutshell, anywhere between 20/100 and 20/200 depending on several factors, especially BCVA

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## Dorn

I have a -11 diopter level of correction and that barely allows me to drive a vehicle - need a note at DMV to say I can see at 20/40. Several years ago my prescription started changing within a few months. My lenses cost over $1,000/pair and take over 2 weeks to be made.

After visiting several eye doctors, it was determined I need cataract surgery. Some how this was missed. I am only 60 years old so I never even considered cataracts. I though my blurred areas were caused by a massive amount of 'floaters' there since childhood. I knew I could not see as well as I had previously. 

If you or a patient has a severe visual correction which starts changing greatly, please check for cataracts. 

Does anyone know what I am going to do after the first eye is done and I will have a visual difference of -11 diopters. I have not been able to wear contact lenses in the last 30 years. I do not like the thought of patching one eye for 4-6 weeks.

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## Uncle Fester

> I have a -11 diopter level of correction and that barely allows me to drive a vehicle - need a note at DMV to say I can see at 20/40. Several years ago my prescription started changing within a few months. My lenses cost over $1,000/pair and take over 2 weeks to be made.
> 
> After visiting several eye doctors, it was determined I need cataract surgery. Some how this was missed. I am only 60 years old so I never even considered cataracts. I though my blurred areas were caused by a massive amount of 'floaters' there since childhood. I knew I could not see as well as I had previously. 
> 
> If you or a patient has a severe visual correction which starts changing greatly, please check for cataracts. 
> 
> Does anyone know what I am going to do after the first eye is done and I will have a visual difference of -11 diopters. I have not been able to wear contact lenses in the last 30 years. I do not like the thought of patching one eye for 4-6 weeks.


Prepare to be flamed. You're outside of posting parameters.

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## braheem24

Dont be so Optimistic Fester :D


You can ask your ophthalmologist if he thinks it's safe to do the eyes 1 week apart instead of 6, it's a common practice in some office but only your doctor knows if you're a candidate.

We cannot however give you ophthalmic or medical advice on optiboard

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## Fezz

> I have a -11 diopter level of correction and that barely allows me to drive a vehicle - need a note at DMV to say I can see at 20/40. Several years ago my prescription started changing within a few months. My lenses cost over $1,000/pair and take over 2 weeks to be made.
> 
> After visiting several eye doctors, it was determined I need cataract surgery. Some how this was missed. I am only 60 years old so I never even considered cataracts. I though my blurred areas were caused by a massive amount of 'floaters' there since childhood. I knew I could not see as well as I had previously. 
> 
> If you or a patient has a severe visual correction which starts changing greatly, please check for cataracts. 
> 
> Does anyone know what I am going to do after the first eye is done and I will have a visual difference of -11 diopters. I have not been able to wear contact lenses in the last 30 years. I do not like the thought of patching one eye for 4-6 weeks.


 
Please review the posting guidelines:

*This forum is for Eyecare Professionals. Consumers are allowed to post in the Just Conversation forum and non-optical topics only. Please be aware that any questions involving optics or eyecare may be removed. These kinds of questions should be discussed with a qualified eyecare professional who has examined you and is familiar with your situation.*

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## DragonLensmanWV

Yeah, who knows how you found this five year old thread, and that is outside the normal boundaries  of posting guidelines. Your doc can tell you these things, but honestly, most of them are not too experienced with your situation. 
I am.

As Braheem said, see how close your doc can schedule them to be done, because you WILL have to patch one eye or the other between surgeries. I was -15 when I had them done. Afterwards, you will have a new appreciation for what you have missed all these years.
Good news is - use newly operated eye for viewing tv and in the house, use unoperated eye for driving.
Take a few days off after getting the second one done to readjust to totally new world's size, it will be larger than what you're used to, so it will take a few days to accommodate.

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## OHPNTZ

> If you or a patient has a severe visual correction which starts changing greatly, please check for cataracts.



Wow, you know I never thought of that!!!  Of all the things...:idea:

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## Aeusuke

How to convert diopters to visual acuity. This is only an estimate. It only works on negative diopters.
(Diopter times Diopter) plus 1.1 times (20)
For example: Pretend your prescription is -0.25D
(0.25*0.25)+1.1*(20)=23.25
So -0.25D= 20/23.25
Another example: -1.00D
(1*1)+1.1*(20)=42
So -1.00D= 20/42
Here is a list:
-0.25D= 20/23.25
-0.50D= 20/27
-0.75D= 20/33.25
-1.00D= 20/42
-1.25D= 20/53.25
-1.50D= 20/67
-1.75D= 20/83.25
-2.00D= 20/102
-2.50D= 20/147
-3.00D= 20/202
-3.50D= 20/267
-4.00D= 20/342
-5.00D= 20/522
-6.00D= 20/742
-7.00D= 20/1002
-8.00D= 20/1302
-9.00D= 20/1642
-10.00D= 20/2022
This may vary with some individuals and is not 100% guaranteed.

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## wmcdonald

> 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.
> 
> 
> ...


As stated previously, the eye is organic and not exact. I have not seen a chart specific to hyperopes or myopes, only Egger's Chart Logic that can be found in Borish's Clinical Refraction, and relates to refractions conditions for a large population of folks this early scientist describes. You are asking for a definitive answer to a moving target, especially for only hyperopes. Variation in accommodative status, as well as other related clinical issues make that a tough nut to crack. Egger's studies nearly 200 years ago measured the average VA of a large number of people over many years, and it has stood the test of time. But as he clearly indicated it was to be used as a starting point only. An example of how it may have been used is during the early days when there were no ODs, only Opticians and Ocularists, and self-selection was common. If we wanted to know if a patient was a hyperope or a myope we used trial lenses, and this helped those pioneers reduce chair time.

Sorry......I did not realize until now how old this thread is!

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## fjpod

Lol...I find it hard to believe that an "eyedoc" does not know of the very loose relationship between visual acuity and hyperopia.   Anybody smell consumer here? 

As old as this post is,  I guess,  who cares?

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## wmcdonald

Yes.....this is a consumer, but I surely bit. And it is very old! My bad.

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## Dr. Bill Stacy

quite a few years ago I helped develop the "Dead Horse Equation" on sci.med.vision.   It was a fun exercise, but kind of a silly one due to all the variables mentioned in this thread.  It's kind of like trying to get a formula for how much weight you will gain or lose on a certain caloric intake.  You'll get some pretty decent averages, but the outliers will always confound you. (e.g. the runners vs. the couch potatoes, or the kids vs the oldsters).

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## Happylady

Wow, I was a -2.50 10 years ago and now I'm  -.75 and a -1.00 with about -.75 and -1.00 astigmatism also.

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## lifeboatpres

> you WILL have to patch one eye or the other between surgeries.


I didn't bother to patch my eye between surgeries and my worst eye was -17.25 diopters before surgery. The worst mishap I had during the nearly three weeks before the second surgery was that I knocked over a drink. I did often close an eye to make my vision tolerable.

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## Jack Smith

20/10: Plano
20/15: Plano
20/20: Plano to -0.125
20/25: -0.25 to -0.375
20/30: -0.5 to -0.75
20/40: -0.875 to -1
20/50: -1.125 to -1.25
20/60: -1.375
20/70: -1.5
20/80: -1.625 to -1.75
20/100: -1.875 to -2
20/120: -2.125
20/160: -2.25 to -2.375
20/200: -2.5 to -2.625
20/250: -2.75 to -3
20/300: -3.125 to -3.375
20/400: -3.5 to -4

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