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


--------------------------------------------------------------------------------

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'
11/9/2005, 6:10 am Link to this post Send Email to Myope5   Send PM to Myope5
 
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!


I typed this in another forum whose subject was "diopters to visual accuracy"


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.
11/10/2005, 10:38 am Link to this post Send Email to Myope5   Send PM to Myope5
 
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!


This verson below has been rounded to .25
It takes your 20/20 BCVA, compenstating for glasses minification. Please see my first post for the 3 most popular charts including the one below.


A. -0.75 .... 20/30
B. -1.00 .... 20/40
A. -1.25 .... 20/50
B. -1.50 .... 20/60
A. -1.75 .... 20/70
B. -2.00 .... 20/80
A. -2.25 .... 20/100
B. -2.50 .... 20/120
A. -3.00 .... 20/150
B. -3.50 .... 20/200
A. -4.00 .... 20/250
B. -4.50 .... 20/300
A. -5.25 .... 20/400
B. -6.00 .... 20/500
A. -6.75 .... 20/600
B. -7.25 .... 20/700
A. -8.00 .... 20/800
B. -9.00 .... 20/1000
A. -10.00 .. 20/1200
B. -11.00 .. 20/1400
A. -12.00 .. 20/1600
B. -13.50 .. 20/2000
A. -15.00 .. 20/2400
B. -16.50 .. 20/2800
A. -18.00 .. 20/3200
B. -20.25 .. 20/4000
It becomes quite silly and moot past 20/4000
so I havent bothered doing the math past that.


I havent made an astigmastic chart, there really is no need. Just consider asigmastim about half as blurrifying as myopia. -1 diopters of asigmastim blurs as much as -.5 of myopia. However asigmastim is evil in that it blurs from near and far. Your vision would be 20/25 on the 20' eyechart and 20/25 on the nearpoint chart with -1 astigmastim. With -1 myopia it would be 20/40 on the 20' eyechart but 20/20 at 1 meter and 20/25 at 2 meters. If you can accomodate, itll be clear as near as your accomodation will let you.

Example guy is -4.5 with -1.5 astigmastim. His distance vision would be as blurred as a -5.25 myope, however his near vision would be least blurry at 9" but still have a 20/30 blur due to -1.5 astigmastim. Fine print may be difficult or impossible to read and larger print somewhat blurred.


Want more examples? Guy B has -2.50 OD with -1.25 cylindar, -2.25 OS with -.75 cylindar. His vision with glasses is 20/25 in each and both eyes.
give him a half diopter "penelity" because his 20/25 starting point is what a -.5 would get with 20/20 BCVA. His astigmastim would add about -.75 myopia. This brings the total to about(-2.5 + -.5 penelity + -.75 for astigmastim = -3.75) making him 20/250 in that right eye. (-2.25 + -.5 penelity + -.50 for astigmastim = -3.25) for 20/200 in the left.

My brother is -1 with -.5 cyl. and -1.25 with -.75 cyl. His BCVA is 20/20 to 20/25 so give him a -.25 diopter "penelity" and we get:

-1 + -.25(for astigmastim) + -.25(penelity)
for a total of a cumulative blur of -1.5 which yields 20/60 which he is from my testing to see what he could read on my snellen chart.
-1.25 + -.5(for astigmastim) + -.25(penelity)
for a total of a cumulative blur of -2 which yields 20/80 which he is from my testing to see what he could read on my snellen chart.

Note that I round to the nearest .25 diopters so I rounded up for his -.75 cyl.
his -.5 cyl. blurs as much as -.25 myopia but it blurs from all distances.


I see 20/80(right eye) 20/100(left eye) with -3.25 glasses. My near point is 20cm in left and 22cm in right. Therefore I have -5 and -4.5 of myopia. -1.75 in left, -1.25 in right remain with -3.25 glasses. My astigmastim is irregular(plus I have high order abberations) which cant really be corrected by glasses. Therefore I have a BCVA of 20/25(left) 20/30(right) compenstating for glasses minification. Looking at the following BCVA's I can conclude I have -1 diopters(left) and -1.5 diopters(right) of uncorrectable irregular astigmastim. It blurs half as much as myopia, but from all distances. Therefore I have a -.5 and -.75 permaent blur(wavefront lasik might be able to fix this but thats another story)

-1.75 for 20/100 because of the -.5 "penality" due to -1 irregular astigmastim. Without the penality, I would be seeing 20/70.

-1.25 for 20/80 because of the -.75 "penality" due to -1.5 irregular astigmastim. Without the penality, I would be seeing 20/50.


My near vision is 20/25(left) 20/30(right) because of the irregular astigmastim. Note that I still need -2.5 glasses for the 16" near point or ill have a -2.5 diopter myopic blur(plus the penality) If the glasses are more than my 2.5 diopter accomodation, I get a hyperopic blur. My -5.5 glasses give me +3 diopters at the 16" near point resulting in +.5 hyperopia therefore reducing my 20/25 to 20/30 for near.

Last edited by Myope5, 11/11/2005, 7:49 am
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!


This lady had a bad lasik experience and ended up with 20/60 BCVA. She complains that the computer monitor is blurry. Take someone with -1.5 diopters and 20/20 with glasses, he would see 20/60 on the snellen but at 2/3 meters from the computer, he would be seeing 20/20 clarity. The poor lady has 20/60 blur at all distances while the -1.5 myope has zero blur at 2/3 meter. Depending how much he can accomodate, he can see clear from nearer. If he has +5 diopter accomodation and add the -1.5 myopia, he has 6.5 diopters resulting 20/20 clarity down to 6 inches!

with my -3.25 glasses and sitting 2/3 meters from the computer, I experience -.25 myopia blur in left eye, +.25 hyperopia in right eye(which easily gets accomodated)I therefore see a 20/30 blur in each and both eyes which is half the blur she experiences. with -2.5 glasses its -1 and -.5 myopic blur. With the "penality" I get a 20/50 to 20/60 blur. My less myopic right eye would see a bit clearer despite a lower BCVA.


interesting eh? Its not just your diopters but your astigmastim(regular and irregular) and your BCVA that determines your UCVA vision. The better your BCVA is, the better your UCVA will be with the given amount of myopia and/or astigmastim. All astigmastims blur, but regular astigmastim gets factored into the BCVA thereby avoding the "penality" while the irregular kind cant be corrected.

a -1 myope with -1 regular astigmastim sees 20/60 UCVA and 20/20 BCVA. His glasses pescription would be read -1 sphere, -1 cylindar.

a -1 myope with -1 irregular astigmastim sees 20/60 UCVA and 20/25 BCVA. His glasses pescription would be read -1 sphere.


People think the guy without an astigmastim in his glasses pescription is better off but he is NOT! Both see equally well without correction, but their BCVA's tell the full story otherwise. Of course if the guy with regular astigmastim had it ommited from the glasses, he would be plano with -1 astig which blurs as much as -.5 myopia and therefore be seeing 20/25. The thing is the guy with irregular astigmastim has no choice as it cant be corrected! Well with modern wavefront lasik technology it may in part or full but with no guarantees and possible complications.


Not everyone has a 20/20 BCVA(compenstating for glasses minification) because each eye is different. Its what the eye allows. Some have exceptionally perfect corneas with very few high order abberations and no irregular astigmastim. They would have a BCVA at or near the retina's capabilities. I have seen some achieve 20/10 and the occasional lucky guy with 20/8 with glasses, even with minification, which in itself wasnt significent due to their mild myopia anyway. Others only get 20/30, 20/40 or even worse! I am not bad off being only one line away from a perfect 20/20 BCVA(compenstating for minification) I do not know the percentage with 20/20, 20/25, 20/30, etc BCVA but I know the averages. For my amount of myopia, the average is 20/20 with contacts, 20/25 with glasses and im only a line below that. For amounts -10 or more(very severe myopia) the average is less than 20/20 with contacts and even worse with glasses due to the fairly significent minification. I would be considered average for my BCVA with around -12 diopters of myopia. If I was -12, the 20/30 line would be minified to 20/24. My true BCVA(as opposed to BSCVA or best spectacle correction) is one without minification. This much myopia is bad for the retina and the stretching and thinning of the retina may/could result in a degradation of visual quantity and quality. Therefore I may be 20/40 BSCVA or 20/30 true BCVA if my eyes worsen to -12! The average -12 has a 20/30 spectacle correction and 20/25(actually 20/24.2 but 20/25 is close enough for rounding purposes plus theres no 20/24.2 line on snellen charts) true correction.


This lucky lady is -10.5 and can see some of the 20/20 line with glasses. That line has been minified to 20/16.5 she did say she will no longer able to see 20/20 at -12 diopters. Thats 20/16. She does see all of the 20/20 clearly and sharply with contacts. Therefore her true BCVA falls somewhere between 20/20 and 20/15. Perhaps 20/17.5 which explains the difficulty she now has with 20/20 at -10.5 which has been minified to 20/16.5 My math tells me that if she reaches -25 diopters, the 20/25 line would be minified to 20/16.6 therefore making it very difficult to see. Since contacts have vitrually no minification, theres no point even factoring it in, its too small to be significent except perhaps in the worst cases with thick -25+ RGP contacts and even that, it would be of low significence, especially in relation to the poor BCVA.
As long as her pathalogical myopia hasnt yet caused retina, macular and other occular problems, her true BCVA shouldnt really drop. Her spectacle BCVA will drop but thats purely from minification. The average BSCVA of a -27 is 20/60, 20/40 for true BCVA. Her case could be considered well above average. I know a guy in his mid -20s seeing 20/25 with RGP which is two lines better than the average true BCVA for such super severe myopia. I know another of -16.5 seeing 20/40 with glasses which is near average(its average at 20/40 at -18) His true BCVA would be exactly 20/30 which can be achieved with contacts. The 20/40 he sees with glasses has been minified exactly the same size as the 20/30 line with contacts. Both are equally good and equally small. You could call the 20/40 line he sees with glasses 20/30 and the 20/30 line with contacts 20/30 and it would make no difference! The 20/40 BSCVA is an artificial limit purely on spectacle minification. He did say hes starting to have trouble with his retinas and even had a retina tear which was quickly fixed. This explains the loss of two lines of true BCVA. My loss of one line of true BCVA is probably due to irregular astigmastim of the cornea.
11/11/2005, 7:49 am Link to this post Send Email to Myope5   Send PM to Myope5
 
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!


some optometrists and people think I must have "something wrong" if I can not achieve 20/20 BCVA. This is not always the case. Also with a spectacle BCVA of 20/30, this isnt what id consider bad. If it was worse than 20/40 then yes unless I had a good deal of myopia. A diopter of irregular astigmastim and/or some extra high order abberations is all it takes to decrease your BCVA to 20/25. I dont think I ever was 20/20, I remember being 20/50 corrected to 20/25 with -1 glasses. Its just the shape of my eye, more specifically the topography of the cornea that allows your BCVA's capability. 20/25 to 20/30 isnt bad enough to limit you, well unless you wanted to be a pilot or join the army or specific carreers. Those require 20/20 BCVA in one or both eyes usually. If my problem is with the retina(which I really doubt) theres nothing that can be done nor do I want to risk anything, not for 20/30 BCVA. 20/100 maybe, 20/200 ok yea. If its in the cornea, wavefront lasik or intacs may fix that. emoticon
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!


reguarding astigmastim blurring half as much as myopia, read below:


Spherical soft lenses are used primarily when a spherical refraction or a comparatively low amount of refractive astigmatism is present (i.e., -3.00D -0.50D x 180, where the 0.50D of astigmatism is less than 1/4 of the spherical component). When low amounts of refractive astigmatism are present, a practitioner may prescribe the contact lens power as a Spherical Equivalent (adding half of the cylinder power to the sphere power). All contact lens powers greater than 4.00D must be vertex corrected for the corneal plane.


see? If someone has -1 astigmastim and doesnt want torics, then he needs a -.5 diopter boost in regular contacts. Say hes -3.5 with -1 cyl. He would experience as much blur as a -4 and need -3.25 contacts instead of -2.75. Of course -1 to -1.5 cyl. is the limit to avoid torics. You still can but the additional cyl. will then have to be ignored and you may get less than 20/20 or whatever your BCVA is. cyl. isnt the same as sphere but it can be approximated for contacts and especially determining UCVA. You can determine UCVA by considering cyl. about half as bad/blurry as sphere. -2 sphere and -2 cyl. blurs as much as -3 sphere for example.
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!


Below are from patients 6/10/99 at my office *note 3 ODs involved )


I have made no attempt come up with a formula


20/100 -2.25-0.50x015 20/20
20/100 -2.00-0.50x025 20/20 20 yrs old


20/50 +1.25 20/20
20/50 +1.25 20/20 50 yo


20/20 +1.00-0.25x170 20/20
20/20-- +1.25-0.25x170 20/20 17yo


20/400 +6.75-4.00x180 20/50-1
20/400 +6.75-3.25x170 20/70- 54yo


20/30 +0.25-1.25x175 20/25
20/30 +0.25-1.25x180 20/25 6yo


20/200 -1.50-0.50x170 20/20 25yo autorefractor=
-8.25-1.25x170
20/200 -1.25-1.25x005 20/20 (OD note "accom spasm") -6.50-1.00x005


20/400 +3.50-2.00x180 20/400 (amblyopia)
20/200 +3.50-2.00x175 20/20 59yo


20/200 +1.50 20/50 (?? had been using CL LT eye only)
20/100 +1.50 20/20 47yo (I don'thave at home copies of
all of pat's chart)


20/50 +0.25-0.50x075 20/40 (cataracts & glaucoma C/D 0.8 by 0.8 OU


20/100 +0.75 -1.00x090 20/40- 74yo


20/50+2 +1.00-1.00x075 20/20
20/20 Plano 20/20 36yo


20/200 +4.50-2.00x005 20/30
20/100 +3.00-0.75x150 20/30 66yo


20/200 -2.00-0.25x180 20/200
20/200 -2.00-0.25x165 20/200 12 yo


20/80 none bacterial conjunctivitis
20/80 none 7 yo


hand movement +11.75 20/30 aphake (Mexico surgery 20 yrs
ago)
at 3 ft (hm@3') +12.25-0.75x160 20/40 67 yo


20/400 -3.25-0.50x177 20/20
20/400 -3.25-0.75x178 20/20 24 yo


20/40-2 -0.25-0.25x90 20/20
20/40-2 -0.25-0.25x80 20/20 7 yo


hm@3' no help scheduled for cat sx
20/50 +1.25-1.00x008 20/20 49 yo IOL (pseudophake)


20/40 +1.25-0.75x165 (but glasses not prescribed)
20/40 +1.25-0.75x175 >3 yo<


20/20 +0.50 (bifocals 1.50 add)
20/20 +0.75-0.25x090 47yo


20/400 -3.00 20/20
20/400 -4.00 20/20 39yo


20/60 -0.75-1.00x090 20/40++
20/70 -1.00-0.50x150 75 yo


20/30 +0.75-0.50x165 20/30 (glasses not prescribed)
20/30 +0.75-0.50 x180 20/30 4yo


20/200 +2.75-1.00x085 20/25+
20/200 +2.75-1.00x090 20/25+ 64yo


most of above over 40 were given multifocal lenses.


I note that only 8 of 48 eyes did not have astigmatism although some of the 48
had only 0.25.


It depends on the type of dioptric refractive error (myopia.hyperopia,
astigmatism),squinting, age, present ocular conditions (cataracts) and
all. But generally, for myopia, I find -1.00d will correspond with 20/30
to 20/40 unaided; -2.00 with 20/70 to 20/80; -3.00d with 20/100 to
20/200; -4.00 about 20/400. Usually,astigmatism corresponds to 1/2 of an
myopic correction. For example,-2.00d of astigmatism will correspond to
-1.00 of myopia. Hyperopes are much more difficult because of
manifest(present) vs latent (hidden) types. Hopes this helps.

my comments
I agree with the above. -1 is a small refractive error and results in half vision between UCVA and BCVA. Take my sister's friend she could easily see the 20/15 line and when I handed her a +1 reading glasses she was reduced to 20/30 with -1 of simulated myopia. Back when I was 12 and got my first -1 I was 20/50 corrected to 20/25.
-2 diopters indeed does correspond between 20/70 and 20/100 for most people. -3 typically yields 20/150 UCVA but depending on your BCVA, it can be 20/100 or worse than 20/200! -4 will typically yield 20/300 but if the eyechart has nothing between 20/200 and 20/400 then youll be recorded as 20/400.

"I am -2.00 and can see 20/40...so I wouldn't put too much stock in this
chart........."

Either he squinted a little, did it in bright light(pinhole effect) or has a 20/10 BCVA. 20/40 is indeed unusual for -2 diopters reguardless. I would be expecting more along the lines of 20/70 or 20/100.
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!


At age 4, she was -2.5 with acuity 20/80, at age 5, she was -4 with
20/200. These are all unaided vision.


The above is the case of this girl with some pseudomyopia, she has

since improved to -1.5 and presumbly 20/40. Given the above figures,

its likley her BCVA was 20/15! I know this because I know this older

lady who had 20/15 BCVA and was seeing 20/100 without much trouble and

if she tried, could barely make out the 20/80 very blurry. Another guy

remarked that(from experience?) that -2 diopters and the persons

looking at a snellen were testing at 20/70 or 20/80 accuracy. He goes

on to add a -3 diopter refractive error yields 20/100 to 20/200 depending on BCVA among other factors. I believe you may need an incredable 20/13 BCVA to get 20/100 UCVA at -3 and on the other end, a 20/25 BCVA for 20/200 at -3. 20/20 would be in the middle at 20/150.
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!


My results with both eyes tested together(OU)(If my BCVA was 20/20):


plano 20/30+(20/20)
-.25 20/30(20/20 but blurry)
-.5 20/40(20/25)
-.75 20/50(20/30)
-1 20/60(20/40)
-1.25 20/70(20/50)
-1.5 20/80(20/60)
-1.75 20/100(20/70)
-2 20/120(20/80)
-2.5 20/150(20/120)
-3 20/200(20/150)
-3.5 20/250(20/200)
-4 20/300(20/250)
-4.5 20/400(20/300)
-5 20/500(20/400)


Lets assume my pescription is now -5 in the left eye(20cm near point) and -4.5 in right(22cm near point) this would make me barely 20/400 but since I have astigmastim, this puts me down to 20/500. It doesnt take much improvement to get to 20/300. I am going to assume I have -.25 cylindar in the left and -.75 in the right. If we do spherical equivalent, the left is only -.25 worse!
To simplify things, lets do a spherical equivalent for both eyes. Ill just say -5.25 for left and -4.75 for right. Not quite enough to see 20/400 in either eye. I only need 1/4 diopter improvement to see 20/400 and 3/4 to see 20/300! I want to get a cycoplegic refraction. I believe ill definately be 20/300 in one or both eyes and possibily 20/200! I then can improve on my pseudomyopia and achieve a much better UCVA with the reduction of just one or two diopters! I started at 20/600 UCVA being -5.75 spherical equivalent! I believe I can get to 20/300 which would mean I doubled my vision with vision improvement emoticon emoticon emoticon
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Registered: 05-2005
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Re: So how bad is -1 diopters? -2? -10? My eyechart research!


Theres some controversity reguarding the rules of vision accuracy. Its widely accepted you need to see a majority of the letters without randomly guessing and getting lucky. The more letters of a given line you have the subject read, the more reliable your results will be. I say 10 is a good minimum number of test letters where you need to get more than 2/3 right so thats 7 out of 10 to "pass". However getting all 10 right is certainly better.


Someone seeing a solid 100% 20/20 is certainly better than someone barely seeing/guessing and getting slightly more than 2/3 of the line right. However both have very good vision and the differences is in reality very small, perhaps on the order of 20/20 vs. 20/21 or 20/22. I have stated that the following values are if your correctable to 20/20(compenstating for minification) If you can see more than 2/3 of 20/20, its enough to count and close enough to be within my diopter chart guidelines. Someone seeing 100% 20/20 and another guy seeing 70% of 20/20 are both close enough to for example be 20/100 at -2.25 however someone only seeing 1/3 or 1/2 of 20/20 may not quite see 20/100 at -2.25
He could perhaps be 20/120.

There is also the issue of "just barely perceivable" This is what my diopter chart guidelines are for. For the lower amounts of myopia, the variance is going to be alot smaller. Also theres not going to really be "barely percievable" Because for small amounts of blur, its pretty straitforward but for large blurs, its more open to guessing and interpretation. I will explain each number with my opinion.






This verson below has been rounded to .25


A. -0.75 .... 20/30
Everyone should be seeing that line with over 90% accuracy. If your having trouble then your also having trouble with 20/20 BCVA as well. Those who only see 20/40 arent going to fully be corrected to 20/20. Likewise those who have an easy time seeing this line and can see some or all of 20/25 are solid 20/20 and likley to see some 20/15


B. -1.00 .... 20/40
The great majority of people will see this line with over 90% accuracy. Those who fall closer to 20/50 are partial 20/20 at best. Likewise those who can see some or all of 20/30 are likley to be able to resolve part of 20/15

A. -1.25 .... 20/50
The majority of people will resolve this line with at least 90% accuracy. Some may fall closer to 20/60, only seeing half of this line, not enough to count. Likewise, its pretty common to be able to resolve half or even all of 20/40 with a solid 20/20 BCVA

 
B. -1.50 .... 20/60
Most people will pass this line with a diopter and a half of myopia. Depending how solid your 20/20 BCVA is, you may pass 20/50 with more than 2/3 accuracy or only see half of this line making you a 20/70 but with viturally 100% accuracy

 
A. -1.75 .... 20/70
This line may be blurry but if your a solid 20/20 you ought to not have trouble passing this line. There are still some who can pass 20/50 but they are partial 20/15 if not better. Likewise, some people fail this line. If you are having trouble seeing even 20/80 your BCVA probably wont stand a chance at passing 20/20 and you may not even be 100% accurate at 20/25

 
B. -2.00 .... 20/80
One optometrist said his patients with this pescription usually pass this line. A fair number of people can still pass 20/70 and they have solid 20/20 BCVA to say in the least. Some people may have trouble with this line despite still passing 20/20 and may be closer to 20/100 which is still fine but if your worse than that I doubt your correctable to 20/20

 
A. -2.25 .... 20/100
A solid 20/20 BCVA should pass this line. The deviation is typically from 20/70 to 20/150 depending on your BCVA. Some people despite passing 20/20 fall a bit shy of 20/100

 
B. -2.50 .... 20/120
Many people with this pescription have difficulty with 20/100. This is not a common line on snellen charts and usually the next step up is 20/150 if you fail 20/100. In fairness, youll score between the two with this amount of myopia. You should see 100% of 20/150 if your a solid 20/20 and some people can see part or enough to pass 20/100 especially with a solid 20/20 BCVA. If your better than 20/20 you may see better than 20/100 UCVA. I know one lady whos 20/15 and she can see this line no problem and barely pass 20/80

 
A. -3.00 .... 20/150
Although commonly stated 20/200, those with a solid 20/20 BCVA in fact should be seeing better than 20/200 and good enough to pass this line. Everyone correctable to 20/20 should pass 20/200 at minimum. Some people may not pass this line despite passing 20/20 but should pass 20/200 or I question their ability to see even partial 20/20 because I can pass 20/20 with a solid 20/30 BCVA

 
B. -3.50 .... 20/200
Although a seemly high dioptric amount, someone whos a solid 20/20 ought to pass 20/200. Theres no excuse not to see 100% of 20/200 with a BCVA better than 20/20. Those having trouble or unable to resolve 20/20 BCVA may be considered 20/300 UCVA or more perhaps 20/250 although ive never seen anything between 20/200 and 20/300 on snellen charts

 
A. -4.00 .... 20/250
Not a line seen on snellen charts, netherless its mentioned because many people with four diopters do fall between 20/200 and 20/300. It however is approperate to consider them 20/300 since this is the next line after 20/200. Most people will resolve 20/300 with BCVA in the 20/20 to 20/30 range. If unable to pass this line, your BCVA isnt very good. On the flipside, BCVA better than 20/20 is known to pass 20/200 in fact one young girl passed 20/200 with a -4 lense giving her 20/15 BCVA

 
B. -4.50 .... 20/300
Most people will consider you 20/400 with this dioptric amount. I can pass 20/400 with this diopters despite only seeing a solid 20/30 BCVA. One whos a solid 20/20 probably should pass 20/300 with this diopters. There is still debate if -4.5 should be 20/300 or if its "too much" for 20/300.
 
A. -5.25 .... 20/400
Most people will consider you worse than 20/400 with this diopters and its probably true many do fall just shy of this. Even being a solid 20/20, this line wont be easy to read. -5 diopters seems to be the generally accepted limit for 20/400 but I know two people who passes 20/400 at -5.5
Even if you can barely pass this line, being -5 and especially -4.75 certainly will make this line much easier and probably 100% pass too.

 
B. -6.00 .... 20/500
Not a common line on snellen charts, netherless its between 20/400 and 20/600. The majority of people would be considered 20/600 with this amount of myopia but in truth they may be able to resolve a little better than that. This is probably the limit for 20/400 and your gonna need to be at least 20/15 if not better to pass 20/400 with this much myopia which is already considered high myopia.

 
A. -6.75 .... 20/600
Probably need to be a solid 20/20 to pass this line. Being better than 20/20 or having a bit less than -6.75 diopters will certainly help achieve 100% accuracy of this line. Ive been told you need to be closer to -6 than -6.75 to pass 20/600. The range varies pretty widly at this point with some -5 diopter guys still being considered 20/600 while on the flipside, ive heard a few -7 diopter guys passing this line.


 
B. -7.25 .... 20/700
Never seen this line on a snellen chart. In truth, people with this much myopia can safely be considered 20/800. I dont think many will be able to pass 20/600 with this much myopia, although those with a solid 20/15 or better BCVA could be capable of passing 20/600. Most people should still pass 20/800, even I can when simulating this much myopia by wearing a plus lense.

 
A. -8.00 .... 20/800
Typically, the largest line on nearly all snellen charts. To be honest, I have not seen anything larger than 20/400 except on my own custom snellen charts I made myself. Even that, I would have to make by hand anything larger than 20/600 which needs two pages to fit, 20/800 wont even fit. 20/400 is the largest that will fit on a single page so I understand why the space constrictions limit most charts to 20/400. Also many people consider it a moot point if you cant see 20/400 then your vision is really bad, period. I dont have much experience in diopters vs. 20/xxx for the higher amounts of myopia because not very many people are this myopic and also few charts even go to 20/800 so I just hear high myopes say "im so blind, I cant even see the big 20/400 E" I do know one guy whos -7.5 barely seeing 20/800 who got lasik and ended up 20/20. Perhaps this is where my diopters to 20/xxx formula begins to break down. If very, very few people are seeing 20/800 at -8 but alot more people are seeing 20/400 at -5.25 then my formula of where 50% more myopia results in 50% visual accuracy ends here. Perhaps it becomes more expotentional beyond this point. My only experience was simulating with *two* plus lenses and my friend said due to the magnification, this isnt accurate. I did compenstate but she says its not the same as real myopia.

Last edited by Myope5, 12/23/2005, 3:34 pm
12/23/2005, 2:55 pm Link to this post Send Email to Myope5   Send PM to Myope5
 


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