Prescription Conversion
Leslie Levere
Leslie Levere
My prescription for both my eyes is the same, -4.25 and I was wondering
what that was if you convert it to the 20/20 vison saying. For
instance, are my eyes 20/70? I'm sure they're probably worse, but
that's what I want to know. If anyone could help, I'd really appreciate
it.
Thanks,
Leslie
Eyeglasses to see
Blurry words on blackboards, and
The moon's dark oceans
Raymond A. Chamberlin
<lele...@nortelnetworks.ca> wrote:
>Hi, I have a question, and I was wondering if anyone could help me.
>My prescription for both my eyes is the same, -4.25 and I was wondering
>what that was if you convert it to the 20/20 vison saying. For
>instance, are my eyes 20/70? I'm sure they're probably worse, but
>that's what I want to know. If anyone could help, I'd really appreciate
>it.
Diopters = +-[Log(20/xxx)]/.43 = +-2.3Log(20/xxx) = +-Ln(20/xxx)
See the quote of John Connally at:
-4.25 comes out about 20/1400.
Ray
Mike Tyner
Raymond A. Chamberlin <ra...@tsoft.net> wrote in message
> Diopters = +-[Log(20/xxx)]/.43 = +-2.3Log(20/xxx) = +-Ln(20/xxx)
> -4.25 comes out about 20/1400.
Except most -425's can see better than that.
-MT
William Stacy
Mike Tyner wrote:
But not bad for a 1st approximation of a young myope with large pupils
in a dark room and no squinting.
At least as meaningful as 20/400 or 20/800...
The dead horse equation strikes again.
Bill Bill (RC apparently likes my double name effect, so I'll put 'em
on one line. At least I don't do double/triple posts)
Raymond A. Chamberlin
<wst...@ix.netcom.com> wrote:
>
..........
>
>The dead horse equation strikes again.
>
>Bill Bill (RC apparently likes my double name effect, so I'll put 'em
>on one line.
And Buffalo Bill-Bill rides off again into the sunset on his dead
horse.
>At least I don't do double/triple posts)
Hey, I had help from Net problems on those. . .or maybe it was those
fertility drugs I took. ;-)
Ray
John Franklin
You can not concvert apples to oranges.
Leslie Levere wrote:
>
> Hi, I have a question, and I was wondering if anyone could help me.
> My prescription for both my eyes is the same, -4.25 and I was wondering
> what that was if you convert it to the 20/20 vison saying. For
> instance, are my eyes 20/70? I'm sure they're probably worse, but
> that's what I want to know. If anyone could help, I'd really appreciate
> it.
>
Raymond A. Chamberlin
wrote:
>The is NO conversion. Your Rx and your vision are two different things/
>You can not concvert apples to oranges.
Not so. That is a tactic of optoms to keep a mystique that expands
their domain. See my first post in this thread above. If you don't
like that data and math from persons posting to this NG, check out
this early published source on the subject (not by an optom, of
course, but by a person with relevant academic credentials):
http://x35.deja.com/[ST_rn=ps]/getdoc.xp?AN=287133691&CONTEXT=932409638.1491992658&hitnum=0
Ray
hen...@my-deja.com
I think that you may be misunderstanding what the 20/20 is vs.
prescription.
The prescription is a measure of your refractive error...how much
curvature of a lens it takes to focus light on the back of your eye.
This has little to do with visual acuity...some people have naturally
better blur interpretation than others. Some people have smaller pupils
(which reduces blur) than others.
The other measure is of how well you can see..to be honest, what it is
without your glasses/contacts does not mean a darn thing. It is what
you see with your glasses/contacts (probably 20/20) that counts.
Remember that there is a huge population of people that can never see
20/20 even WITH glasses or contacts...people with albinism, glaucoma,
cataracts, etc. Also remember that 20/100 (or any other number) for
one person, is totally different than that same measurement for another.
Bottom line is, your uncorrected acuity is irrelevant, only your
corrected acuity matters...unless you wander around without your
glasses/contacts all the time.
Jen
Sent via Deja.com http://www.deja.com/
Share what you know. Learn what you don't.
Raymond A. Chamberlin
Well, that is the magical way in which optoms want the public to see
their mystical discipline. But the facts of physical reality -- and
even psychophysical reality -- follow the mathematics of defocused
images, which is what is asked for here, as do all lens systems,
organic and inorganic. I don't know why the basic theory (I would
assume based on the Fourier Transform) of this isn't posted somewhere
on the Web, but I have mentioned, in my earlier posts to this thread,
both 1) consistent results a poster to this NG a couple years ago got
from analyzing the accumulated client data of an optometrist posting
to this NG, and 2) same from a paper published many decades ago by a
Stanford physiological psychologist.
Certainly, 1) all manner of problems with the eyes, optic nerves and
brains of people can lower their visual acuities, and 2) the fact that
Snellen charts, using characters only arrived at historically from the
Roman alphabet for a different purpose, are stupidly usually used by
optoms to obtain their 20/xx acuity figures throws additional
anomalous noise into any real results -- IT STILL REMAINS that the
optical resolution of a lens system (correlating closely to human
visual acuity in eyes good except for spherical refractive error)
varies analytically as a well-defined (logarithmic) function of the
degree of defocusing (as measured in diopters) of that system. And
the people who keep very logically asking for this information, really
only through their intuitive good sense, are simply asking for the
empirically rough results of this eye-inherent mathematical
relationship -- for the case when an eye, etc. *doesn't* have all
sorts of other problems than simply spherical (and, of course, toric
could be analyzed) refractive correction.
So I tell you one thing, as long as I post to this NG, you optometric
people are NOT going to play this "professional" game unchallenged.
Each time one of you posts this stuff, it shall be pointed out that
such is done, either through IGNORANCE OR LACK OF INTELLIGENCE OF THE
OPHTHALMIC POSTER -- OR -- AS AN INSULT TO THE INTELLIGENCE OF THE
PERSON ON THE STREET, who may not have gone through an ophthalmic
study program but who has good common sense.
Ray
Raymond A. Chamberlin
>
..........
>
>Bottom line is, your uncorrected acuity is irrelevant, only your
>corrected acuity matters
If the main reason for your lowered acuity, as measured in the form
20/xx by means of a Snellen or other so-calibrated eye chart without
correction, is simply spherical defocusing -- then either formula
given in my earlier posts will tell you, fairly closely, how many
diopters of spherical correction, of the appropriate sign, you require
in order to optimize your visual acuity. THUS, THE ***BOTTOM LINE***,
IN THE ***REAL*** WORLD, IS THAT YOUR UNCORRECTED ACUITY IS ***NOT***
IRRELEVANT.
Ray
>
.....
>
Mike Tyner
Raymond A. Chamberlin <ra...@tsoft.net> wrote
> So I tell you one thing, as long as I post to this NG, you optometric
> people are NOT going to play this "professional" game unchallenged.
> Each time one of you posts this stuff, it shall be pointed out that
> such is done, either through IGNORANCE OR LACK OF INTELLIGENCE OF THE
> OPHTHALMIC POSTER -- OR -- AS AN INSULT TO THE INTELLIGENCE OF THE
> PERSON ON THE STREET, who may not have gone through an ophthalmic
> study program but who has good common sense.
And as long as you continue to post to this NG, correlations of r < .5 or .6
will still yield worthless predictions.
-MT
toxguy
>
> >Hi, I have a question, and I was wondering if anyone could help me.
> >My prescription for both my eyes is the same, -4.25 and I was
wondering
> >what that was if you convert it to the 20/20 vison saying. For
> >instance, are my eyes 20/70? I'm sure they're probably worse, but
> >that's what I want to know. If anyone could help, I'd really
appreciate
> >it.
>
>
>
>
http://x29.deja.com/[ST_rn=ps]/getdoc.xp?AN=285015714&search=thread&CONT
EXT=932102304.1881276478&HIT_CONTEXT=932102191.1881669685&hitnum=0
>
>
which is kinda close. at least i'll take that since the link quoted
*doesn't work*.
the most recent "thread" on this topic i could find was
titled '20-1000 in diopters?' by ross drewe, 10/28/97. he mentions
hirsch's findings, a log-log plot and a similar equation.
lessee if ray wil direct us to this connolly posting....
i don't doubt it, i just don't like being sent on wild goose chases.
--
smile.it makes the world wonder what you're up to.
<<GO BLUE JAYS!!>>
<<2z...@my-deja.com>>
hen...@my-deja.com
What you say in your posts is fundamentally correct...if you are
dealing strictly with an optical system comprised of a series of
lenses, a light source, and a place to focus it....but we are not.
As an engineer, you tend to miss the human factor of vision, the visual
perceptual component. And as you have glaucoma, you should even better
appreciate that whatever your acuity is, it is NOT the same as a what a
person with a healthy eye would see at the same uncorrected acuity.
By your equation, someone with a -4.25 Rx would see 20/1400 or
thereabouts....I am -4.00 and uncorrected see about 20/400. My
husband, who is a -5.00 with substantial cyl component sees 20/200
uncorrected. Make mathematical sense? Of course not, but we are not
mathematical creatures...his blur interpretation is better than mine,
or perhaps his pupils are smaller, or perhaps it is because he has
achromatopsia and nystagmus. Too many variables here to be plugging
into oversimplified equations.
BUT...uncorrected acuity does NOT matter, unless you spend your real
life time uncorrected, which most people do not on a regular basis.
Jen
Raymond A. Chamberlin
>
............
>
>http://x29.deja.com/[ST_rn=ps]/getdoc.xp?AN=285015714&search=thread&CONT
>EXT=932102304.1881276478&HIT_CONTEXT=932102191.1881669685&hitnum=0
>>
>> -4.25 comes out about 20/1400.
>>
>> Ray
>
>which is kinda close. at least i'll take that since the link quoted
>*doesn't work*.
I just tried this link and it works for *me*. I don't think you have
to be signed in at deja.com just to *view* posts, but maybe you do.
>the most recent "thread" on this topic i could find was
>titled '20-1000 in diopters?' by ross drewe, 10/28/97. he mentions
>hirsch's findings, a log-log plot and a similar equation.
The above URL gets you to a post of mine, of 10/26/97, in that thread,
which quotes a post by John Connolly dated on or after 10/20/97 in
that thread.
Try to go, from whatever post you can reach in that thread, over to
the deja.com tree of that thread and there find that post of
Connolly's and maybe his earlier one based only on Stacy's data for
myopes. I think, however, that deja.com often gets threads chopped
up, because I can seldom find all of their posts, but you can try to
approach things that way.
>lessee if ray wil direct us to this connolly posting....
>
>i don't doubt it, i just don't like being sent on wild goose chases.
What did you get when you tried that URL? The first attempt of mine
tonight got me "Internal Server Error". Make sure you end up with
only the actual URL in your browser slot -- no '>'s or anything else
extra, and make sure the whole URL (which is split in your newsreader)
is contiguous (no spaces) in your browser slot.
Ray (There's a flock of 'em up there now.)
Raymond A. Chamberlin
wrote:
>
...........
>
>And as long as you continue to post to this NG, correlations of r < .5 or .6
>will still yield worthless predictions.
Woe unto the world when it should rely on the mathematics of
optometrists.
Ray
Raymond A. Chamberlin
>Hey Ray...
>
>What you say in your posts is fundamentally correct...if you are
>dealing strictly with an optical system comprised of a series of
>lenses, a light source, and a place to focus it....but we are not.
For practical purposes, we *ARE*!!! Statements to the contrary are
simply appeals to the public to forget physical science and *BELIEVE*
in holy optometric priests whose mystical ritualistic styles are
cramped by science.
>As an engineer, you tend to miss the human factor of vision, the visual
>perceptual component.
Stacy's data, both on myopes and heteropes, is *empirical*. Hirsch
used empirical data. Connolly mathematically analyzed the data. The
vast majority of myopes and hyperopes do not have other significant
eye problems that would *significantly* disrupt the equivalence shown
by these equations.
>And as you have glaucoma, you should even better
>appreciate that whatever your acuity is, it is NOT the same as a what a
>person with a healthy eye would see at the same uncorrected acuity.
My left eye is *mostly* out with glaucoma and has *no* central vision.
Of course, I would and *could* not apply any of these psychooptical
formulae (which *include* the "human" visual-perceptual factor -- when
it's working right) to this eye. My other eye has *no* problem at
all, other than the presbyopic-hyperopic refractive one. It/me fit(s)
the formula very well.
>By your equation, someone with a -4.25 Rx would see 20/1400 or
>thereabouts....I am -4.00 and uncorrected see about 20/400. My
>husband, who is a -5.00 with substantial cyl component sees 20/200
>uncorrected.
Obviously, I would have to check those claims out to see what kind of
games are being played here -- that make your and your husband's eyes
so much better than all those used as data to consistently determine
the empirical relationships referenced in this thread.
>Make mathematical sense? Of course not,
You better believe it doesn't! From my experience, and that of many,
many other persons, including mathemeticians and statisticians,
there's no reason on earth that one should expect many of today's
optometrists or physicians to make mathematical sense. They feel that
cramps their style *all* to hell.
>but we are not
>mathematical creatures...
I do not believe either of you are so far out of kilter that you do
not fit the referenced models within their limited parameter ranges,
in respect to your eye-brain readout, GIVEN NO FUNNY BUSINESS FROM THE
BRAIN SIDE. Of *course*, you can use your brain to foul up the
optical and normal-JND-perception visual channels. But we see here
plenty of other people who *didn't* play games and *do* fit the curve.
The brain part in this is assumed to operate linearly (on a log
scale).
>his blur interpretation is better than mine,
The issue appears to be, not the small difference between the two of
you, but the large difference you claim, for both of you, from what
the subject empirical relationships show. Differences in "blur
interpretation" are down in the mud.
>or perhaps his pupils are smaller, or perhaps it is because he has
>achromatopsia and nystagmus. Too many variables here to be plugging
>into oversimplified equations.
See, that's exactly the fun and games ODs and MDs play: As soon as
their numbers or whatever don't fit reality, they start bringing in
the kitchen sink. You can bet that most of the people who post the
question these empirical formulae answer HAVE *NO* OTHER EYE PROBLEMS
THAT SUBSTANTIALLY UPSET THE VALIDITY OF THE RESULTS OF THE USE OF
THESE FORMULAE IN RESPECT TO THEIR VISION. They do *not* have
achromatopsia (not that I think *that* would make any difference) or
nystagmus; they simply have other than an emmetropic refractive
situation. You, and most of the rest here, immediately seize the
opportunity to shove the inaccurate, expensive and annoying OD, MD or
whatever crafty operator into the path of fixing up simple optics in
the best and most efficient manner. You aren't saying anything more
sophisticated than is someone who says I can't sweep the floor,
because there are some insects on it, which requires that I call an
exterminator.
>BUT...uncorrected acuity does NOT matter, unless you spend your real
>life time uncorrected, which most people do not on a regular basis.
In the vast majority of cases, uncorrected acuity *DOES* indicate
fairly closely the power of correction needed to optimize it. That is
what these equations are all about. The people wanting answers to
approximately how much correction they will need, given their measured
uncorrected acuity of 20/xx, are asking a straightforward question
that can be, in almost all cases, easily answered with these
equations. Your above statement is *TOTALLY* IRRELEVANT TO THIS QUERY
OF THEIRS, but irrelevance is often the name of the game with ODs,
MDs, attorneys and many others who hate mathematics and simple
mechanistic solutions and love to play the HEALER ROLE. . .and make an
undeserved profit from it. I'd like to force such people to hire
somebody to keep an accounting of their auto mileage with maps,
because, of course, the odometers in their cars cannot accurately
measure the mileage they cover in their cars, due to anomalies in
their tires, the surfaces of the roads they travel and the weather
they experience while driving, etc.
In the case of engineering, the idea is to work yourself out of a
given level of job by making it trivial and doable mechanistically,
and then to go on to bigger and better things -- while most of those
who claim to provide personal services, do all they can to make it so
they do the same old, boring, obsolete ritual, day after day, that
hasn't made any sense, practically speaking, since 1547 or so. How
can they stand that silly role-playing business for so long?
Ray (If Nature had wanted eyes to be fixed, she would not have allowed
ophthalmic practitioners to exist.)
Mike Tyner
.6
> >will still yield worthless predictions.
>
> Woe unto the world when it should rely on the mathematics of
> optometrists.
Yeah, much better it should rely on palm-readers and
self-appointed experts.
-MT
William Stacy
Bill
John Connolly wrote:
> Hi Ray,
>
> I'm still lurking, occasionally.
>
> Some old posts on the "William Stacy Dead-Horse Equation" are below.
>
> John Connolly
>
> --------------------------
>
> On 18 Sep 1997 12:15:23 GMT, w...@ix.netcom.com(William Stacy) wrote:
>
> >So here is the corrected table ("where cyl is greater than -.5 or cyl
> >is null"):
>
> This does not change things much, which is not a good sign for the
> equation. The regression coefficient stays essentially the same (0.420
> changes to 0.421), while the standard deviation improves only a little
> (0.81 diopters to 0.76 diopters).
>
> It is of interest that dropping only one point (-8.25) of the 135 would
> decrease the standard deviation to 0.61 diopters. This comes from the
> propensity of "least squares" fits to give inordinate weight to outlying
> points, because the sum of the _squares_ of the deviations is being
> minimized. Some people use a "rule of thumb" and throw out points that
> have deviations greater than four times the standard deviation, but we
> won't do that here.
>
> I have come to the opinion that the large uncertainty in the measurement of
> 20/xxx is a major problem in an exercise like this. There is, of course,
> little practical incentive to improve this measurement because it has no
> effect on the patient's final vision.
>
> --------------------------------------------------------------
>
> Diopters = [Log(20/xxx)]/0.42 = 2.4 Log(20/xxx)
>
> 20/xxx meas. calc. diff.
>
> 20/40 -0.75 -0.7 0.0
> 20/30 -0.25 -0.4 0.2
> 20/70-- -0.75 -1.3 0.5
> 20/20 -0.25 0.0 -0.3
> 20/25 -0.75 -0.2 -0.5
> 20/40 -0.5 -0.7 0.2
> 20/40 -0.75 -0.7 0.0
> 20/50 -0.25 -0.9 0.7
> 20/60 -1.25 -1.1 -0.1
> 20/60+- -1 -1.1 0.1
> 20/50- -1 -0.9 -0.1
> 20/300 -2.75 -2.8 0.0
> 20/20 -0.12 0.0 -0.1
> 20/25- -0.5 -0.2 -0.3
> 20/25- -0.25 -0.2 0.0
> 20/200 -2.25 -2.4 0.1
> 20/200 -2 -2.4 0.4
> 20/30 -0.25 -0.4 0.2
> 20/100- -2 -1.7 -0.3
> 20/60- -1 -1.1 0.1
> 20/40- -0.5 -0.7 0.2
> 20/80- -1.5 -1.4 -0.1
> 20/30- -0.25 -0.4 0.2
> 20/70 -1 -1.3 0.3
> 20/200 -1.5 -2.4 0.9
> 20/80+ -1 -1.4 0.4
> 20/80+ -1 -1.4 0.4
> 20/400 -3.25 -3.1 -0.2
> 20/400 -3.25 -3.1 -0.2
> 20/400 -2 -3.1 1.1
> 20/50 -1 -0.9 -0.1
> 20/60- -1.5 -1.1 -0.4
> 20/200 -2.25 -2.4 0.1
> 20/200 -2.25 -2.4 0.1
> 20/20- -0.5 0.0 -0.5
> 20/200 -4.25 -2.4 -1.9
> 20/80 -1.5 -1.4 -0.1
> 20/40- -1.25 -0.7 -0.5
> 20/40- -1 -0.7 -0.3
> 20/200 -2 -2.4 0.4
> 20/200 -3 -2.4 -0.6
> 20/25 -0.5 -0.2 -0.3
> 20/400 -4.25 -3.1 -1.2
> 20/20 -0.25 0.0 -0.3
> 20/70 -1.25 -1.3 0.0
> 20/20-- -0.75 0.0 -0.8
> 20/200+ -1.5 -2.4 0.9
> 20/200+ -1.5 -2.4 0.9
> 20/80 -1.25 -1.4 0.2
> 20/80 -1.25 -1.4 0.2
> 20/50+- -0.75 -0.9 0.2
> 20/400 -2 -3.1 1.1
> 20/400 -2.25 -3.1 0.8
> 20/200 -2 -2.4 0.4
> 20/200 -2.5 -2.4 -0.1
> 20/400 -5.5 -3.1 -2.4
> 20/100 -1.5 -1.7 0.2
> 20/200 -1.75 -2.4 0.6
> 20/50 -0.75 -0.9 0.2
> 20/40-- -1.5 -0.7 -0.8
> 20/40-- -0.75 -0.7 0.0
> 20/70 -0.75 -1.3 0.5
> 20/200 -1.25 -2.4 1.1
> 20/200 -1.25 -2.4 1.1
> 20/60 -1.25 -1.1 -0.1
> 20/100+- -1.25 -1.7 0.4
> 20/80- -1.25 -1.4 0.2
> 20/200- -2 -2.4 0.4
> 20/200- -2.25 -2.4 0.1
> 20/60 -1.5 -1.1 -0.4
> 20/20 -0.25 0.0 -0.3
> 20/25 -0.25 -0.2 0.0
> 20/20 -0.25 0.0 -0.3
> 20/30 -0.5 -0.4 -0.1
> 20/100- -0.75 -1.7 0.9
> 20/20 -0.25 0.0 -0.3
> 20/70 -1 -1.3 0.3
> 20/40- -0.25 -0.7 0.5
> 20/50- -1 -0.9 -0.1
> 20/20 -0.12 0.0 -0.1
> 20/300 -2.75 -2.8 0.0
> 20/30- -0.75 -0.4 -0.3
> 20/30- -0.75 -0.4 -0.3
> 20/100 -1.75 -1.7 -0.1
> 20/30- -0.5 -0.4 -0.1
> 20/200 -1.75 -2.4 0.6
> 20/200 -1.75 -2.4 0.6
> 20/400 -3 -3.1 0.1
> 20/400 -3.75 -3.1 -0.7
> 20/50- -1 -0.9 -0.1
> 20/100- -1.75 -1.7 -0.1
> 20/20- -0.25 0.0 -0.3
> 20/80+ -0.5 -1.4 0.9
> 20/80+ -1 -1.4 0.4
> 20/400 -3.5 -3.1 -0.4
> 20/400 -3.5 -3.1 -0.4
> 20/40 -0.75 -0.7 0.0
> 20/200 -2 -2.4 0.4
> 20/200 -2.75 -2.4 -0.4
> 20/200 -2.75 -2.4 -0.4
> 20/20- -0.5 0.0 -0.5
> 20/100-- -3.25 -1.7 -1.6
> 20/100- -1.25 -1.7 0.4
> 20/100- -1 -1.7 0.7
> 20/40- -0.75 -0.7 0.0
> 20/40 -0.5 -0.7 0.2
> 20/40 -1.25 -0.7 -0.5
> 20/20 -0.25 0.0 -0.3
> 20/400 -8.25 -3.1 -5.2
> 20/400 -6 -3.1 -2.9
> 20/80 -2.5 -1.4 -1.1
> 20/50 -1 -0.9 -0.1
> 20/30 -1 -0.4 -0.6
> 20/30 -0.75 -0.4 -0.3
> 20/200+ -1.5 -2.4 0.9
> 20/200+ -1.5 -2.4 0.9
> 20/80 -1.5 -1.4 -0.1
> 20/80 -1.25 -1.4 0.2
> 20/50+- -0.25 -0.9 0.7
> 20/200 -2 -2.4 0.4
> 20/200 -2 -2.4 0.4
> 20/200 -2 -2.4 0.4
> 20/200 -2.5 -2.4 -0.1
> 20/100 -1 -1.7 0.7
> 20/100- -1.75 -1.7 -0.1
> 20/50-- -1.75 -0.9 -0.8
> 20/50-- -1.5 -0.9 -0.6
> 20/40 -0.5 -0.7 0.2
> 20/70 -0.75 -1.3 0.5
> 20/70 -1.25 -1.3 0.0
> 20/100 -1.25 -1.7 0.4
> 20/100+- -1.25 -1.7 0.4
> 20/20 -0.25 0.0 -0.3
> 20/200 -1.5 -2.4 0.9
> 20/200 -1.25 -2.4 1.1
>
> On Fri, 19 Sep 1997 08:02:23 GMT, ra...@sirius.com (Raymond A. Chamberlin)
> wrote:
>
> >As a first-order approximation, at least, for images at a distance
> >large compared to the lens system, defocusing a given distance either
> >in front of or behind a focal plane is obviously the same. The
> >association of 'plus' and 'minus' to convex and concave lenses or
> >equivalent lens systems is obviously an arbitrary convention.
> >Therefore, one should be allowed to put absolute-value signs around
> >both sides of the equation proposed.
>
> Yes! Of course. The anonymous developer of the equation no doubt meant it
> that way, and the meaning was lost by my excessive literal mindedness.
>
> Therefore:
>
> |D| = |[Log(20/xxx)]/0.42| = |2.4Log(20/xxx)| or, for non nitpickers:
>
> D = +-2.4Log(20/xxx) and S.D. = 0.8 for myopia.
>
> If hyperopic data :-) becomes available the constant will change, perhaps
> back toward the original 3.7 (1/.27), and the standard deviation will
> increase. Perhaps separate constants for myopia and hyperopia are
> empirically desirable.
>
> On 19 Sep 1997 15:17:08 GMT, w...@ix.netcom.com(William Stacy) wrote:
>
> >I'll post some hyperopic data for you if you want...
>
> That would be helpful. TIA.
>
> >unlike myopia, where unaided VA is relatively stable with age,
> >hyperopic unaided VA drops with age due to decreasing accommodative
> >amplitude. I've forgotten the precise numbers, but it declines more or
> >less linearly beginning in the 20s, when + 5.00 can be overcome,
> >levelling off at more or less zero at age 55.
>
> I'm sure what you say is correct. However, it is still possible that, at
> each age our hyperope will show the same functional relationship between VA
> and required correction. If so, we will publish and name it the "William
> Stacy Dead-Horse Equation." :-)
VernonH
Chamberlin) writes:
>
>If the main reason for your lowered acuity, as measured in the form
>20/xx by means of a Snellen or other so-calibrated eye chart without
>correction, is simply spherical defocusing -- then either formula
>given in my earlier posts will tell you, fairly closely, how many
>diopters of spherical correction, of the appropriate sign, you require
>in order to optimize your visual acuity. THUS, THE ***BOTTOM LINE***,
>IN THE ***REAL*** WORLD, IS THAT YOUR UNCORRECTED ACUITY IS ***NOT***
>IRRELEVANT.
Ray,
How will the subject know if his acuity "is simply spherical defocusing etc"
????
Here are some VAs uncorrected -Rx -corrected VA & age for you all to play
with.
(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.
Have fun!
Vern
Vernon C. Hammond,O.D.
McAllen, TX 78501