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Re: So how bad is -1 diopters? -2? -10? My eyechart research!

"Although you may feel this way, you have a long way to go. My vision
is much worse than yours (something like -12 the last time it was
checked). I would not want to become much more nearsighted, because
at some point they won't be able to correct it to 20/40, and I won't
be able to drive."

My comments: Glasses minification and especially very high myopia cause significent changes in the retina, thereby reducing BCVA. 20/30 BSCVA is average for -12 but if he has some extra high order aberrations, he may be getting 20/40 with glasses and if he gets more myopic, he may no longer pass the DMV.

"Currently my eye sight is past 20/100. In my case, I have slight astigmatism
Mine is at least and still changing."

My comments: With that pescription, its no supprise he can no longer see 20/100. He may be at 20/150 to 20/200 now depending on his astigmastim and BCVA. He probably has a spherical equivalent of -3 to

"I'm currently in 20/70. I started at 20/40. I feel that I'm nearly blind right now, I can not imagine becoming more nearsighted. My prescription right now is in each eye. It use to be

My comments: That person is just a complainer. I am a good -4 and even I dont consider myself nearly blind at 20/400. I see great from 10 to 12 inches away uncorrected of course. I only correct to 20/30, that person should be thankful his/her UCVA and 20/20 BCVA is great. The diopters vs. 20/xx correlates perfectly with my research and further supports it.

"I read the eye chart last week at a 20/60 in my right and 20/30
in my left. I asked for an interim script for glasses and feel
much better now! Amazing how clear the world can be when fully
I correct to 20/20 on my left and 20/25 on my right, with glasses!
OD :// 090
OS :// 120"

My comments:

This translates to and -1
This is a spherical equivalent of just over -2 in the right eye
so I am supprised hes seeing 20/60 with 20/25 BCVA. It would
concide with my diopter chart if you ignored the astigmastim.
The left eye likewise is also supprising. Maybe he squinted a little
which skewed the results for both eyes? He wouldnt need glasses
if he was really 20/30 in the better eye. I would expect 20/50
with that pescription and 20/20 BCVA.

Last edited by Myope5, 3/10/2006, 6:21 am
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!

my reply to him in another forum. While not diopters to 20/xx" it shows that very high myopia results in decreased BCVA as ive talked about in my previous posts

>First off, I'll like to say thanks
>for this forum. This is a
>great source of information.

You are welcome!

>I'm very near sided (-16 and -
>18) with someastigmatism ( and
>I'm 41 years old,and started wearing
>glasses at 4 years old. Ialso
>started wearing hard contact lenses at
>aboutthe same time. My corrected vision
>has never been 20/20. The best
>I've ever gotten is 20/40.I also
>have very poor night vision.

sorry to hear! If this makes you feel better, I also have never corrected to 20/20 even though my eyes arent as bad as yours. Ive been told my best corrected vision is seeing some of the 20/25 line and all of the 20/30 line. My pescription is in the -4 range. No one in my family can be corrected to a full 20/20 either, but all can to 20/25. 20/20 is perfect vision and very hard to achieve.

>I've seen several optometrists and ophthalmologistsover the
>years, and I have asked why
>they can'tcorrect my vision to 20/20,
>but never got a concise answer.
>Some of the reasons suggested are:

I couldnt correct to 20/20 either and they said my astigmastim, high order aberrations and glasses minification all keep me from perfect 20/20 correctable.

> * The brain/eye hardware for
>vision forms
>at a very young age. Since
>I was probably
>near sided from a very young
>age ( pre
>4 years old), and was not
>corrected initially,
>my "hardware" isn't quite
> right.

sounds possible. Having never seen what good vision was like, you brain may have never developed percise vision. You never knew what it was like to see great.

> * My eye ball is
>not round, so the retina
> is stretched, and as
>a result there are
> fewer light sensitive nerves per
>square inch. This
>results in a grainer picture
> (like a low resolution
>digital camera).

another reason. Stretched retinas have other problems which disort vision.

> * My night vision is
>poor because the focal
> point of the rods and
>cones are different.
>My corrected vision is based on
>the cones (
>daylight vision), so at night my
> corrected vision doesn't
>focus on the
>rods (night vision).

Thats in addition to your high order aberrations.

> * My night vision is
>poor because the optics
> of my contact lenses become
>incorrect as my
>iris grows at night. Improperly focused
> light comes in
>at the edges of the contacts.

Do you see better at night with glasses?

>Does anyone have any "insight" into this

Your glasses minify so your 20/40 may be with RGP contacts while you may see 20/60 with glasses.

>I'm also looking into the Verisyse IOL.
>I've been told I would make
>a good candidate. MyDoctor also thinks
>that it may be possibleto get
>better corrected vision with the
>this sound realistic?



Id say 20/40 to 20/50 is relistic. Theres some risks with clear lens extraction but itll make your life much easier not to be blind without coke bottle glasses. You may still need a thin pair of bifocals for your astigmastim, any residual myopia and your presbyopia.

this guy is -13.5 contacts(should be -17 glasses) he is losing tolerance to RGP contacts

Dont you see much better with your RGP contacts vs. soft? 20/20 is very good vision(corrected, correctable), especially for an extremely high myope like you. I correct to 20/30 with my -4s glasses(due to high order aberrations) but if I ever tried RGP I probably will get 20/20. Youd be around a -17 in glasses! Do you even have an emergency backup glasses or ever wear them, maybe when you wake at night to eat a snack?

anyway there are custom contacts that can be made to -20! another option is get the highest power in the brand you are most comfortable with then wear a thin pair of glasses over them to complete your pescription. I think this kinda sounds silly when there are contacts that fully correct you but some people can only tolerate certain brands and since their pescription is so high and rare, theres no market for companies to mass produce contacts this high. I see many companies go up to -10 or -12 in contacts. If you get a company that goes to -12 contacts, youd only need -2 glasses for the tiny remainder of your pescription. The good thing about this is you can take your -2 glasses off when reading or on the computer to relieve eyestrain and slow down your (pathalogical) myopia progression. (Otis will say stair-case)

Last edited by Myope5, 4/10/2006, 11:40 pm
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!

If I can tolerate orthoK(much easier to do so from the people I know who tell me) itll be worth it. I can remove orthoK when I wake up and all the hassles with it. For the remainder of the day ill have clear, uncorrected vision and I can even swim without worrying about losing a contact because there is none! Your right about forgetting to put in orthoK some nights. Not a big deal if your eyes arent bad, this is where natural vision comes. I can get my -5 down to -3 then orthoK can take care of the rest. Also it takes like 2 weeks to fully regress. Ill regress to maybe -1 at most if I forget a night or two of orthoK and -1 isnt a big deal, my bro is and doesnt need glasses except for driving and even then he isnt legally required to wear glasses to drive, he chooses to do so for good measure. His uncorrected vision is only slightly reduced from his best corrected vision. He sees and reads text from a great distance without glasses. We dont understand why some at -1 make a big deal. They must be so super picky! I asked him at what point would glasses be considered a neccessary and he says at least -2 and in some cases, closer to -3. Therefore if I can improve to -2 I will be almost free from glasses and see quite clearly! Myopia is expotentional and each diopter compounds the blur. I do not know on what expotentional scale this is based on, however -2 is more than twice as bad as -1(about I heard) and -4 is on the order of almost 4 times as bad as -2 from what I hear! Each diopter higher adds alot more to the blur. I heard that if I improve from -5 to -3 Ill be seeing nearly three times better! I know this lady who was -10.5 with so much blur she was nearly blind. When she described how bad the blur was, I shuddered! When I asked her how far she can count fingers, she said I cant really even count fingers! I hold my hand arm length(about 2 feet, short arms) and I just see a pinkish blob! If she drops her glasses, someone has to pick them up or she can spend many minutes fumbling for them by feel. Without her glasses, she bumps into walls and objects! When I asked if she can read the eyechart, she laughed and said, what eyechart? I cant even tell if theres an eyechart, let alone read it!

From what I heard, I have composed the estimated snellen equivalent. One such optometrist who posts online mentioned figures like that which I have shown below:

<-1 = 20/20 or just shy of 20/20
-1 = 20/40 = 20/50
-1.5 = 20/60 = 20/80
-2 = 20/100
-2.5 = 20/150
-3 = 20/200
-3.5 to -4 = 20/300
-4 to -4.5 = 20/400
-5 to -5.5 = 20/600
-6 = 20/800
-7 = 20/1200
-8 = 20/1600
>-8 = cant even count fingers!

comments: less than -1, also referred as "fractional myopia" is so slight, some still see 20/20. Near -1 may cost a line so 20/25(20/30 at worst) just shy of 20/20 in other words. or quarter diopter has never cost a line, often doesnt even make a difference from this optometrist's testing. He says -.5 diopters is usually the smallest where any blur can be percieved this is why you can often have a margin of error of plus/minus .25 diopter.

*If you read my first post, I made my own diopter chart based on my research. The above is the research of one optometrist. It appears to go in line quite well with my own diopter chart. I do question if -6, -7, -8 or more is really that bad but since I have limited research in those high myopia dioptric values, I cant make any assertments till I research further. I have posted before wondering if my diopter chart begins to break down around -6 to -8 instead of keeps going on the linear/expotentional scale I have devised where the diopters results in .5x visual accuracy.

Here is a side by side comparsion to my diopter chart. My results are in (

<-1 = 20/20 or just shy of 20/20(same)
-1 = 20/40(same) = 20/50(same)
-1.5 = 20/60(same) = 20/80(20/70)
-2 = 20/100(20/80)
-2.5 = 20/150(20/120)
-3 = 20/200(20/150)
-3.5 to -4 = 20/300(20/200 to 20/250)
-4 to -4.5 = 20/400(20/250 to 20/300)
-5 to -5.5 = 20/600(20/400)
-6 = 20/800(20/500)
-7 = 20/1200(just below 20/600)
-8 = 20/1600(20/800)
>-8 = cant even count fingers!(below 20/800)

For the lower dioptric values, this optometrist's research concides/agrees with mine perfectly. For more moderate myopia values, he is a little more strict than me in his research on how well one can see. For high myopia -6 and up, our results are way different. I have limited knowlege of the visual accuracy of a high myope -6 or more and of someone with a visual accuracy worse than 20/400 since few charts go past that and none I know go past 20/800.

I recall one optometrist who estimated this -11 lady at 20/3000 based on her counting fingers at a foot and a half(20/2667?) so I guess this -10.5 lady I chatted to(combined with slight astigmastim actually did have a -11 spherical equivalent) and this explains why she couldnt even count fingers at 2 feet! From her description how bad her vision was, she very well may have been 20/3000 or an order of more than 5x worse(now 7x due to my NVI)

To attempt to record the results on an expotentional scale, up to -1.5 it appears to be linear. From the following values, I am recording the expotentional results.

-1 to -1.5 = diopters, worse
-1 to -2 = 2x diopters, worse
-1 to -2.5 = diopters, worse
-1 to -3 = 3x diopters, 5x worse
-1 to -4 = 4x diopters, 8x worse
-1 to -6 = 6x diopters, 20x worse

As you can see, the gap keeps growing between x(times) diopters and x(times) worse.

-2 to -2.5 = diopters, worse
-2 to -3 = diopters, 2x worse
-2 to -4 = 2x diopters, worse
-2 to -5 = diopters, 5x worse
-2 to -6 = 3x diopters, 8x worse
-2 to -8 = 4x diopters, 16x worse

As you can see again, the gap keeps growing between x(times) diopters and x(times) worse.

Someone good at math would be able to estimate how high it goes from there and also graph it. My diopter chart has a linear component so it can easily be graphed. I will keep doing more research and even if I find that my origional diopter chart wasnt quite on the mark, I am leaving it there for simplicity and to show the results of earlier research and will attempt to make a 2nd, revised diopter chart that better reflects additional research.

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Re: So how bad is -1 diopters? -2? -10? My eyechart research!

another case study example. You will see I have posted about 50 examples in my previous posts reguarding the diopter correlation to visual accuracy. I also have mentioned before that -.5 diopter costs only one line and that diopters costs 2 lines.

A 48-year-old female with no significant ocular history presented for
LASIK in April 1999. Preoperative examination revealed uncorrected
visual acuity of 20/160 in the right eye and 20/160 in the left eye.
Best spectacle-corrected vision was 20/20 in both eyes. Cycloplegic
refraction was – :// ×180° in the right eye and – :// ×180°
in the left eye.

my comments: spherical equivalent of -2.5 so this is a little shy of 20/100. I guess the next line on shown eyechart was 20/160.

At 3 months following enhancement of the right eye and 11 months
following LASIK treatment of the left eye, the patient noted that the
vision and dryness symptoms appeared to be improving, especially in the
left eye. Uncorrected visual acuity was 20/20 in the right eye and
20/25 in the left eye. Manifest refraction was – D in the right eye
and – D in the left eye with best spectacle corrected visual acuity
of 20/15.

my comments: This is impossible for her to "magically" improve to 20/15 BCVA. Theres several logic explanations, please refer to the lasik section in my forum. Nonwithstanding the issues with lasik, this example shows the correlation of diopters to UCVA.

Last edited by Myope5, 5/6/2006, 11:53 pm
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!

in another forum, someone said this:

interesting question, and only an approximate answer possible. typically is about 20/40, by vision is 20/80 to 20/100, and at
about 20/200. about 20/400. Above 20/600 or worse.

the real answer depends on the optics of corneal curvature vs axial length
- an eye with steep cornea and average length can be equally nearsighted
with an eye with a flat cornea that is very long - but they may not have
the same uncorrected acuity. Some eyes are and 20/400, just like
some eyes that are

Vision decreases seemingly exponentially with increasing prescription, and
quickly reaches 20/200 or legal blindness. Beyond that blurry is blurry
and hard to distinguish as far as distance vision goes.

my comments:

It seems like almost everyone agrees that -1 corresponds to 20/40(20/20 BCVA is assumed) Ive seen others say it can be 20/30 to 20/50 but thats likley due to BCVA's of better or worse than 20/20. I do disagree on his other assetments. -1.5 is going to definately be better than 20/100 if you correct to 20/20. I remember being 20/70 to 20/80 back when I was -1.5 and I couldnt quite correct to 20/20 either! As for -2 being 20/200, I see that all the time but in reality its 20/100 and even those that cant quite see 20/100, they are not 20/200 but just shy of 20/100. Too bad many eyecharts have nothing between 20/100 and 20/200. -3 is commonly 20/200 but definately better than 20/400. -4 tends to fall at 20/300 to 20/400 and occasionally 20/200 if you have a very good BCVA. -5 however is usually worse than 20/400.

I strongly disagree with cornea curvature vs. axial blur. Its equal for both or contacts and lasik would have unexpected results. It does not matter what is causing diopters of blur, its all the same amount of defocus. Your cornea can be too steep or your eye too long, either way is equal blur if equal diopters of defocus.

I do agree on the exponental blur in respect to diopters. I will explain why. As for 20/200 or worse looking almost the same, thats not true! I am 20/600 uncorrected and I can see a very big difference at 20/200 with undercorrecting glasses. Likewise with reading glasses to get me below 20/1200, I can see so much more blur!
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!

I have devised a new formula that is likley to be much more accurate because it attempts to measure blur from an objective point. I still have my subjective blur formula at the start of this thread.

The new formula takes into account the radius of the blur circle. This is something that gets expotentionally bigger the more myopic you are. For cylindar, take the spherical equivalent. The main formula is based on 20/20 BCVA, compenstating for spectacle minification(you know this by now from my previous posts)For better than 20/20, take a "bonus" for worse than 20/20 take a "penalty" This will be explained in the post below this one. Lets do the main formula first.
radius squared times PI=blur area
blur area divide by 4=blur factor
multiply blur factor by 100 and add 20=UCVA

-8 (
-18 (

Simple, rounded verson:

Havent bothered doing the math past that as 20/7870 means a letter measuring feet large! If you go by my simple formula, you can calculate for any dioptric values!

rounded to snellen eyechart verson:

See post below for countinuation of this formula

Last edited by Myope5, 5/30/2006, 11:04 pm
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!

Countinued from above post.

By now you know my formula. What if someone has a BCVA other than 20/20 which my formula is based on? How will this factor in? Simple! I mentioned in above post about "bonus" and "penalty" Heres how it works:

[col=]20/8= diopter bonus[/col]
[col=]20/10=1 diopter bonus[/col]
[col=]20/13=.75 diopter bonus[/col]
[col=]20/15=.5 diopter bonus[/col]
[col=]20/25=.5 diopter penalty[/col]
[col=]20/30=.75 diopter penalty[/col]
[col=]20/40=1 diopter penalty[/col]
[col=]20/50= diopter penalty[/col]

The logic is simple. If someone has a better than 20/20 BCVA, he has few high order aberrations and possibily higher density of cones. Likewise a lower BCVA means the opposite. The figures above should concide with my diopter chart. For example, a 20/25 BCVA gets a half diopter penalty because half diopter myopia blurs your 20/20 into 20/25. The difference is a 20/25 BCVA has any of a number of factors that glasses can not correct.

There is yet another formula thats more accurate than bonus/penalty for low dioptric values. Its called the blur multiplier. It concides with my other formulas

-.5= blur( blur(20x1.5=30)
-1=2x blur(20x2=40) blur(20x2.5=50)
-1.5=3x blur(20x3=60) blur(20x4=80)
-2=5x blur(20x5=100) blur(20x6=120)
-2.5=7x blur(20x7=140) blur(20x8.5=170)
-3=10x blur(20x10=200)

Minor rounding was used to make it simple to remember and also correspond to actual snellen lines.

Lets compare the accuracy of bonus/penalty vs. the blur multiplier.(bonus/penalty vs. multiplier)

Take a 20/8 BCVA( bonus)

-.5(20/13 vs. 20/10) vs. 20/12)
-1(20/20+ vs. 20/16) vs. 20/20)
-1.5(20/20- vs. 20/24) vs. 20/32)
-2(20/30 vs. 20/40) vs. 20/48)
-2.5(20/50 vs. 20/56) vs. 20/68)
-3(20/80 vs. 20/80)

Take a 20/10 BCVA( bonus)

-.5(20/15 vs. 20/13) vs. 20/15)
-1(20/20 vs. 20/20) vs. 20/25)
-1.5(20/25 vs. 20/30) vs. 20/40)
-2(20/40 vs. 20/50) vs. 20/60)
-2.5(20/60 vs. 20/70) vs. 20/85)
-3(20/100 vs. 20/100)

Take a 20/13 BCVA(.75 bonus)

-.5(20/20+ vs. 20/15) vs. 20/20)
-1(20/20- vs. 20/25) vs. 20/30)
-1.5(20/30 vs. 20/40) vs. 20/50)
-2(20/50 vs. 20/65) vs. 20/80)
-2.5(20/80 vs. 20/90) vs. 20/110)
-3(20/120 vs. 20/130)

Take a 20/15 BCVA(.5 bonus)

-.5(20/20 vs. 20/20) vs. 20/25)
-1(20/25 vs. 20/30) vs. 20/40)
-1.5(20/40 vs. 20/45) vs. 20/60)
-2(20/60 vs. 20/75) vs. 20/90)
-2.5(20/100 vs. 20/105) vs. 20/130)
-3(20/140 vs. 20/150)

You already know the baseline math(for 20/20)

Take a 20/25 BCVA(.5 penelty)

-.5(20/40 vs. 20/30) vs. 20/40)
-1(20/60 vs. 20/50) vs. 20/60)
-1.5(20/100 vs. 20/75) vs. 20/100)
-2(20/140 vs. 20/125) vs. 20/150)
-2.5(20/200 vs. 20/175) vs. 20/200)
-3(20/300 vs. 20/250)

Take a 20/30 BCVA(.75 penelty)

-.5(20/50 vs. 20/40) vs. 20/50)
-1(20/80 vs. 20/60) vs. 20/75)
-1.5(20/120 vs. 20/90) vs. 20/120)
-2(20/170 vs. 20/150) vs. 20/180)
-2.5(20/250 vs. 20/200) vs. 20/250)
-3(20/300 vs. 20/300)

Take a 20/40 BCVA( penelty)

-.5(20/60 vs. 20/50) vs. 20/60)
-1(20/100 vs. 20/80) vs. 20/100)
-1.5(20/140 vs. 20/120) vs. 20/160)
-2(20/200 vs. 20/200) vs. 20/240)
-2.5(20/300 vs. 20/280) vs. 20/340)
-3(20/350 vs. 20/400)

Take a 20/50 BCVA( penelty)

-.5(20/80 vs. 20/60) vs. 20/75)
-1(20/120 vs. 20/100) vs. 20/125)
-1.5(20/170 vs. 20/150) vs. 20/200)
-2(20/250 vs. 20/250) vs. 20/300)
-2.5(20/300 vs. 20/350) vs. 20/400)
-3(20/400 vs. 20/500)

Last edited by Myope5, 6/10/2006, 10:31 pm
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!

I am trying to make a circle blur formula for visual accuracies better or worse than 20/20 but I have a hard time figuring out the math for anything other than baseline 20/20. However I believe using bonus and penelty works just as well. If you see the above post, for myopia up to -3, using bonus instead of blur multiplier tends to give better UCVA than actual. For penelty, it gives worse UCVA than actual. However with BCVA worse than 20/50, always use the penelty formula reguardless of diopters of myopia. For 20/40, use the multiplier up to -2 and for 20/50, up to -1.5 I will do the math for the examples below to save you time. I did not use any rounding(except if results ended in decimal then round to nearest whole number) for -3 and below to show the results of the multiplier. For over -3 I used the rounded to snellen verson instead of simple rounded verson.

20/8 BCVA use multiplier to -3 then bonus of

20/10 BCVA use multiplier to -3 then bonus of

20/13 BCVA use multiplier to -3 then bonus of .75

20/15 BCVA use multiplier to -3 then bonus of .5

20/20 BCVA use multiplier to -3 then no bonus/penelty

20/25 BCVA use multiplier to -3 then penelty of .5

20/30 BCVA use multiplier to -3 then penelty of .75

20/40 BCVA use multiplier to -2 then penelty of

20/50 BCVA use multiplier to -1.5 then penelty of

I hope this makes sense! This is what your objective blur should be.

Last edited by Myope5, 6/12/2006, 5:34 am
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!

As of October 1994, according to Taylor's doctor, her vision was 20/25 without glasses and 20/20 with glasses, and her correction was diopter. Taylor says she still has some trouble with night glare and needs glasses to drive at night, but she's delighted with the results. "For the first time in my life that I could remember, I could see my feet in the shower," she says.

My comments: Although generally considered 20/30, its possible to be 20/25 at with factors like good blur perception, small pupils, bright light(eye exams should be in dim light) slightly better than 20/20 BCVA but not fully 20/15. If you look at my blur multiplier, she could be 20/16.7 times 1.5 for 20/25 since you use Another possibility is she is between -.5 and so either lens would get her to 20/20, no one can tell such a small difference, quarter diopters is the smallest thats why its measured this way and not in tenths.

My brother is 20/60 in his -1 sphere, -.5 cylindar eye and 20/100 in his sphere, cylindar. A more recent test revealed 20/50 in his -1 sphere and 20/100 in his sphere. BCVA was 20/20- in the better eye, 20/25 in the worse. The -1 lens in the better eye when tried in the worse got him 20/40 with undercorrection given 20/25 BCVA. -.5 undercorrection yielded 20/30 instead of 20/25. This goes concisely with my objective blur chart.

Last edited by Myope5, 7/12/2006, 4:04 am
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!

I found more diopter conversions, diopter to 20/x

Refractive index is measured in diopters. A diopter is a unit based on the focal length (power) of a lens. A person with one diopter of myopia sees about 20/50 without corrective lenses. This means they see objects at twenty feet that people with normal vision see at fifty feet. For people who have one diopter of myopia, objects would begin to blur at three to four feet and they would need glasses for board work, movies, and driving. A person with three diopters of myopia would have 20/400 vision without correction. He or she would need to wear corrective lenses all the time. Without glasses, these people would only be able to see about one foot without a blurring of their vision.

my comments: Sounds very close or about right for how much blur -1 diopter causes. They would see perfect from near at 39 inches, or a little over 3 feet. I doubt you experience 20/400 blur from -3 it should be more like 20/300 or even 20/200! Your near vision would be 13 inches or just over a foot. diopter of myopia reduces vision to 20/40 and the visual efficiency is reduced to 83% (20/20 is 100% visual efficiency). 20/40 vision is the cut-off used in most states for getting a driver's license. At or above diopter of uncorrected myopia, you will fail the vision test to get a driver's license.
• diopter of myopia reduces vision to 20/80 level and the visual efficiency is reduced to 58%.
• diopter of myopia reduces vision to 20/200 level and the visual efficiency is reduced to 20%. 'Best corrected' vision worse than 20/200 is the 'legal definition of blindness'. Therefore at or above diopter of 'uncorrected' myopia the eyesight is reduced to a vision-level that defines 'legal blindness'. Without glasses or contact lenses, a myope of D sees what a legally blind person is able to see.

my comments: diopters more commonly blurs to 20/30, but for someone with slightly less than 20/20 BCVA, he may experience 20/40 UCVA. -1.5 tends to blur a little less than 20/80, generally 20/60 to 20/70 in eyes that correct to 20/20. For 20/25 BCVA, 20/80 UCVA sounds right. -2.5 is a pretty good estimate for 20/200 UCVA and another reason is alot of eyecharts have no lines between 20/100 and 20/200. Someone correctable to 20/20 possibly will see a little better than 20/200 at -2.5, perhaps 20/160. Ive noticed that -3 is generally the limit for 20/200 UCVA if 20/20 BCVA. -2.5 is a little less than that, a little better than 20/200

Q. What is a Diopter?
A. A diopter is a unit of measurement of the lens focusing power. Each 1/4 of a diopter of nearsightedness will blur a person's vision by 1 to 2 lines on the eye chart. Therefore, the following are approximate uncorrected values: = 20/60 = 20/200 = 20/400 = 20/800 = 20/1,200 = 20/2,000

my comments: Those figures came from a lasik website and are exaggerated to make people believe that their eyes are so bad they must run out and get lasik! At least they are pretty close on the mark for -1, the other lasik website states youd see 20/50. -1 is a very common prescription and seemly a popular first glasses prescription. Ive done much reserch on -1 and it appears that 20/50 is the most common result/figure/estimate/value. Ive seen the 20/50 value for -1 in over 20 different places. Ive seen anywhere from 20/25 to 20/200 acuity. No one with normal 20/20 to 20/25 BCVA is going to see worse than 20/50 to 20/70 with only a single diopter of myopia. An optometrist said in a message board that most of his -1 patients(usually children) see 20/40 with some seeing 20/30. BCVA is often 20/20 and sometimes 20/15. He also said at -2 vision is 20/80 or so.

It seems that alot of sites throw out 20/200 for -2 diopters. Probably a rounding thing and also because most eyecharts have no lines between 20/100 and 20/200. Someone could be just shy of 20/100 but be marked down as 20/200 as its the next line up
 emoticon I would say -2 corresponds to 20/100, this is the case per my objective blur chart.

For -3, I see figures of acuity show 20/200, 20/300 or 20/400. -3 is probably going to be 20/200 or a bit worse like 20/250 for most people with 20/20 BCVA.

for -4, most figures put it at 20/400, but some say worse than 20/400 or mention its the point of "count finger" vision. There is no way -4 blurs to 20/800, im near or at -5 in the worse eye and even I can see 20/800 easily and even 20/600 although barely. I know someone else who was -5 and he measured 13 feet to see the 20/400 E. I recall reading an army website say reguarding passing 20/400 UCVA requirements and they said if you are -4 or less, you "should" pass, if not ask for a second opinion and get tested again. If you are -4.5 you have an even chance to pass/fail. If you are -5, nearly all will fail, they throw in the towel and get lasik. If you are more than -5, forget it, dont even bother.

For -5, you are almost certain to be worse than 20/400 accroding to my objective blur chart. Most healthy eyes should manage 20/600 and any that cant see even 20/800 have some occular pathalogy with poor BCVA worse than 20/40.

For -6 your probably gonna have a hard time seeing 20/800 and some with less than great blur interpretition or slightly worse than 20/20 BCVA, you may be at 20/1000 or even 20/1200. There was someone at -7 who was tested at 20/1200. Probably stood 6.7 feet from the 20/400 E to arrive at that. Because standing 2 meters away cancels half diopter, he was in essence 20/1200 at -6.5

> if someone is -4.5 sph, is that 20/100, 20/200, or what?

Optometrist says: Too many variables for a formula. I'd guess your uncorrected VA is 20/400 to
20/600 if your eyes are healthy.

my comments: That makes sense per my objective blur chart. Would be the limit of 20/400. Id say 20/500 sounds more like it

The two measures are not related in a way that is predictable, uncorrected
acuity depends not only on Rx but on light level, pupil size, lid squinting,
your individual willingness to guess and your ability to deduce letters from
there shape, test distance (whether 5 ft, 10 ft or 20 ft). If you want to
know your unaided acuity, have it measured. With an Rx over -4, by rule of
thumb, you likely have unaided acuity worse than 20/400.

My comments: You can control the variables. The standard for testing vision is indoors in low light with the eyechart illuminated. Pinhole effect should be eliminated with dilated pupils of 6mm or larger and minimized with 5mm pupils. Squinting is an absolute NO NO. One guy was -4 and 20/200 with 20/25 BCVA. I told him thats impossible and he finally admit he squinted a little. I said that doesnt count, its cheating. He would likley be barely 20/400 per my objective blur chart. Test distance should be 20 feet to simulate infinity. This person did say -4 is the cutoff for 20/400 as it will be so blurry as to barely be able to discern.

Yes. There are a lot of us.
20/400 would take about Diopters to correct to 20/20.
20/600 would take about Diopters to correct to 20/20

I myself need about D to correct my right eye to 20/20,
which is so much that it doesn't make any sense to try
to write it in 20/ notation.
I need about D to correct my left eye to 20/20.

My comments: How does this person know? And he could test it himself to see if hes 20/400 or even 20/600 in the eye. I would put him at 20/400 in the better eye and 20/1000 in the worse.

*countinued on post below*

Last edited by Myope5, 7/22/2006, 3:47 am
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