Diopters to Visual Acuity

[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?

[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

[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.

[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.

[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

[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.

[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.

[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:

[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.

[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.


"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.

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!

[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?

[wmcdonald]

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

[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).

[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.

[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.

[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