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Home > Archive > Lasik Eyes Surgery > February 2006 > OT Anyone understand prescriptions?
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OT Anyone understand prescriptions?
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| I had Lasik a few years ago and am very happy with he result. Only problem
is a slight astigmatism in my left eye that's more noticeable when I am
tired on in low light. therefore I decide to get a pair of glasses for
driving, especially at night.
I had my eyes tested at two opticians (long story, not very interesting) and
the prescriptions, to my uneducated view, look quite different
The are
1) RIGHT Sph Plano Cyl -0.50 Axis 173
LEFT Sph +0.25 Cyl -1.25 Axis 75
2) RIGHT Plano Cyl nil Axis nil
LEFT Sph -1.00 Cyl +1.75 Axis 170
I went back to the 2nd optician for an explanation and his assistant said
"Oh yes, they're more or less the same, it's just that Mr xxx transcribes
them differently - he doesn't use minus values". now I admit I'm not very
well up on interpreting a optical prescription but even to me that sounds a
bit suspect!
Any comments?
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| doctor_my_eye@msn.com 2006-02-25, 9:53 pm |
| Here's the facts on the quick. Lets look at the left eye. First,
think of your Rx as a set of co-ordinates. The doctor is going to bend
light into your eye to hit the sweet spot on the center of your macula.
He is calling for the three dimensional formula for that light. The
horizontal dimension is at axis 165, with perfectly level being 180.
The vertical dimension is axis 75. The "y dimension" is how deep your
eye is. At axis 75, the power of your eye is +.25. 90 degrees away,
at axis 75, the power is -1.00. Your amount of astigmatism is the
mathematical difference between those two axis, hence the interval
between =.25 and-1.00 is 1.25.
So, the answer the optician gave you is basically correct. The
optometric profession writes the meridian with the most plus as the
axis, the ophthalmologists are taught to put the least plus first.
Hence, an OD's RX has a minus number in the 2nd column, but an MD has a
plus number. They are calling the same co-ordinates from a different
starting point.
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| Ragnar 2006-02-25, 9:53 pm |
| This is the first useful post that Minarik has put out in over a year.
See if you can make it two in a row.
On 21 Feb 2006 11:09:14 -0800, "doctor_my_eye@msn.com"
<doctor_my_eye@msn.com> wrote:
>Here's the facts on the quick. Lets look at the left eye. First,
>think of your Rx as a set of co-ordinates. The doctor is going to bend
>light into your eye to hit the sweet spot on the center of your macula.
> He is calling for the three dimensional formula for that light. The
>horizontal dimension is at axis 165, with perfectly level being 180.
>The vertical dimension is axis 75. The "y dimension" is how deep your
>eye is. At axis 75, the power of your eye is +.25. 90 degrees away,
>at axis 75, the power is -1.00. Your amount of astigmatism is the
>mathematical difference between those two axis, hence the interval
>between =.25 and-1.00 is 1.25.
>So, the answer the optician gave you is basically correct. The
>optometric profession writes the meridian with the most plus as the
>axis, the ophthalmologists are taught to put the least plus first.
>Hence, an OD's RX has a minus number in the 2nd column, but an MD has a
>plus number. They are calling the same co-ordinates from a different
>starting point.
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| nunayabizinez@yahoo.com 2006-02-25, 9:53 pm |
| Go find a bus to jump under, pestilence. You're an ignorant, lying lump
of excreta who couldn't discern a useful post from a truckload of
manure.
Ragnar wrote:[vbcol=seagreen]
> This is the first useful post that Minarik has put out in over a year.
> See if you can make it two in a row.
>
> On 21 Feb 2006 11:09:14 -0800, "doctor_my_eye@msn.com"
> <doctor_my_eye@msn.com> wrote:
>
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| CatmanX 2006-02-25, 9:53 pm |
| Once, all scripts were written in plus cyl form. This was because the
cyl was ground on the front surface.
With changes in eikonic lens design, cyls became ground on the back
surface in the 60's to reduce field distortion, and hence we need to
write the script in minus cyl form to reflect back surface cyls. People
who write in plus cyl form are out of date and actually asking for the
cyl to be ground on the front surface. This will make the floor slope
when you get your new glasses.
As an aside, the same principles are now being used on the new
generation of multifocals such as Ipseo and SolaOneHD. The multifocal
design and script in laser etched on the back surface to improve
reading zone size and improve optics.
dr grant
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| Ragnar 2006-02-25, 9:53 pm |
| In other words, one method is more appropriate for optometrists who
are prescribing glasses, while the other method is more appropriate
for ophthalmologists who aren't prescribing glasses but are measuring
the refractive error.
The people who make the lenses just punch the numbers into the lens
grinding machine to figure out. So either prescription will work.
I once got a prescription where the lens for one eye was ground to a
completely incorrrect prescription... so it's not a bad idea to have
your optometrist check the lenses after you get them.
On 21 Feb 2006 12:31:04 -0800, "CatmanX" <drgrant@ozemail.com.au>
wrote:
>Once, all scripts were written in plus cyl form. This was because the
>cyl was ground on the front surface.
>
>With changes in eikonic lens design, cyls became ground on the back
>surface in the 60's to reduce field distortion, and hence we need to
>write the script in minus cyl form to reflect back surface cyls. People
>who write in plus cyl form are out of date and actually asking for the
>cyl to be ground on the front surface. This will make the floor slope
>when you get your new glasses.
>
>As an aside, the same principles are now being used on the new
>generation of multifocals such as Ipseo and SolaOneHD. The multifocal
>design and script in laser etched on the back surface to improve
>reading zone size and improve optics.
>
>dr grant
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| doctor_my_eye@msn.com 2006-02-25, 9:53 pm |
| Grant is correct, and Ragnar is close to getting this guess right. The
actual reason that ophthalmologists write in plus cylinder notation and
optometrists write in minus cylinder is the relative age of the two
professions. Ophthalmology has been around for centuries, it is as old
as the practice of medicine itself. So, as Grant eluded, the
ophthalmological profession wrote in plus cylinder for at least a
century before minus cylinder lenses were invented. Optometry has been
a profession, as we know it, for under 100 years. As a matter of fact,
the man that is considered "the Father of Modern Optometry", Dr.
Borish, is actually still alive today and lectures occasionally. The
optometric profession adopted minus cylinder as their own notation
because minus cylinder lens grinding was being invented and growing as
this new profession grew. They are the same prescription, just calling
one axis first instead of another. So the quick conversion rule is.
(1) Add the first and second number in the Rx, keeping their sign...(2)
change the sign of the second number from - to + (or + to-), and (3)
Turn the axis 90 degrees. Wow...you just converted any optometrist's
Rx to an M.D.s...or visa versa.
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| Ragnar 2006-02-25, 9:53 pm |
| My god.. you did it! TWO useful messages in a row. Do you think you
can go for three?
This is your best post ever.
On 22 Feb 2006 11:03:08 -0800, "doctor_my_eye@msn.com"
<doctor_my_eye@msn.com> wrote:
>Grant is correct, and Ragnar is close to getting this guess right. The
>actual reason that ophthalmologists write in plus cylinder notation and
>optometrists write in minus cylinder is the relative age of the two
>professions. Ophthalmology has been around for centuries, it is as old
>as the practice of medicine itself. So, as Grant eluded, the
>ophthalmological profession wrote in plus cylinder for at least a
>century before minus cylinder lenses were invented. Optometry has been
>a profession, as we know it, for under 100 years. As a matter of fact,
>the man that is considered "the Father of Modern Optometry", Dr.
>Borish, is actually still alive today and lectures occasionally. The
>optometric profession adopted minus cylinder as their own notation
>because minus cylinder lens grinding was being invented and growing as
>this new profession grew. They are the same prescription, just calling
>one axis first instead of another. So the quick conversion rule is.
>(1) Add the first and second number in the Rx, keeping their sign...(2)
>change the sign of the second number from - to + (or + to-), and (3)
>Turn the axis 90 degrees. Wow...you just converted any optometrist's
>Rx to an M.D.s...or visa versa.
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| doctor_my_eye@msn.com 2006-02-25, 9:53 pm |
|
O=2EK., I've been playing around with explaining ophtalmic Rxs on
lasikflap.com, so here's that little ditty.
LASIK Flap Forum Index =BB General Discussion =BB Primer on understanding
our prescriptions?
Posted: Wed Feb 22, 2006 2:31 am
Truly
So many patients do not understand the written prescription they
receive when they have a refraction.
I saw that Dr. Minarik posted something on alt.lasik-eyes to explain
how the prescriptions are both written and derived. Was hoping that
something like that would appear here?
Posted: Thu Feb 23, 2006 2:55 am
DrMinarik
Joined: 17 Feb 2006
Posts: 6
Location: Rockford, IL
O.K., I'm game to take a shot at this. Since this forum is read by a
lot of different people with different backgrounds, some people who
have a math or physics background will be really bored by this, while
others might find it very difficult. But, I have to start somewhere, so
lets go.
For this discussion, imagine we are in a classroom, and I hold a piece
of chalk out in front of the class. I call on you, Truly, waking you up
from your nap in the back of my classroom. I ask you to tell me as
precisely as possible where this piece of chalk is, using as few words
as possible with no doubt being allowed to "chance" where the chalk is.
As it so happens, you just finished reading your homework chapters
about "three dimensional thinking", so you are ready for my challenge.
"That piece of chalk is 12 feet from the front of the room, and
thirteen feet from the side wall", you explain gleefully. But your nap
was too restful, because you only gave me a two dimensional answer. I
take the chalk and start jumping straight up and down. "That's not
enough of an answer" I explain, because all the way up and down while
I'm jumping, the chalk is still 12 feet from one wall and thirteen feet
from the other.
"I get it now!" you add gleefully, "The chalk is also 7 feet from the
floor!"
Ahh, we are finally there...any point in space can be described as long
as you have three dimensions to assign to it. The space from left to
right, or wall to wall in this example, is often called the "x" axis.
The space from the front of the room to the back, in this example,
would by the "y" axis. So, the X and y axis cross each other to form a
two-dimensional set of co-ordinates. Then, when you add the "up and
down", or "ceiling to floor" dimension, you have added the "z" axis.
When you watch a "normal" television, everything is happening in two
dimensions, since all the little moving people on the screen are moving
along an "x" or "y" axis. But, if you put on some "3-D Glasses" and the
people seem to jump off the screen and you can seem to touch them, you
have now added the "z" axis.
Now, let's relate this to opthalmic prescriptions. The exact center of
the fovea in the back of your eye, the location of your most precise
vision, is a little "divot" in the middle of your macula. That little
spot is where the chalk is. I want to bend light into your eye, and I
want that light to hit that exact little spot called the fovea. Where
do I need to send the light? How do I want to get it there? I'm going
to bend light, I'm going to "refract" (bend) light into your eye and
send it to that spot. How can I get to that one spot? I'm going to
supply three dimensional co-ordinates that explain where that spot is,
so that the light that comes along will go to the right spot.
Let's "make up" a prescription. Let's say that Truly's new right eye
prescription is +1.00 -1.00 X 180. What does that mean? The first
number, "+1.00" means that the power of her eye along the x axis is now
+1.00. Along the 180 meridian, which happens to be level with the
horizon, the power of her eye is +1.00. The next number in the
prescription is a "difference" between the x axis and the y axis. So,
if the x axis power is +1.00, the power 90 degrees away (at axis 90) is
1 "unit" less than the power at 180. So, if the power at 180 degrees is
+1.00, the power at 90 degrees is +1.00 minus 1.00, so it is a net
power of zero. So, if the first column of the prescription is the "x"
dimension, and the second column helps you get the "y" dimension, all
is left is the "z". The z number is determined by the numbers, plus or
minus numbers, that you put in those first two columns. So, the power
of Truly's eye at 180 is one Diopter, the power 90 degrees away is
Plano
(or Zero) so her prescription is +1.00-1.00X180. If I shine a beam of
light at her eye, and i bend it through a spectacle lens with the
intent to bend it to that sweet spot, the fovea, the "chalk spot" I
must specify three dimensions, and the beauty of an ophthalmic
prescription is that it takes that beam of light to the exact spot we
want it to, as long as that beam of light hits a spectacle lens that
bends light with this little formula...+1.00-1.00X180. Its all there!
Where is the chalk in relation to the two walls and the ceiling? It
takes a lot of words to describe where the chalk is in relation to four
walls and a ceiling, especially when you consider that an opthalmic
prescription squeezes all that information into a little formula like
+1.00-1.00X180.
Alright, wake up. Tomorrow's homework is due on my desk by morning, and
I expect the answer to the following extra credit question: What did
the Zen Master say to the hot dog vendor?
"Make me one with everything."
_________________
For resources, check www.doctormyeye.com
Ragnar wrote:[vbcol=seagreen]
> My god.. you did it! TWO useful messages in a row. Do you think you
> can go for three?
> This is your best post ever.
>
> On 22 Feb 2006 11:03:08 -0800, "doctor_my_eye@msn.com"
> <doctor_my_eye@msn.com> wrote:
>
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| doctor_my_eye@msn.com 2006-02-25, 9:54 pm |
| There are opticians who have been making glasses for 30 years, but they
have simply "learned the cookbook" and they can transpose and convert
prescriptions effortlessly. But, they often can't imagine what the
numbers actually mean. Hence, this attempt to turn the numbers into 3
dimensional thought. Snatch the pebble from my hand, grasshopper. ;)
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| Ragnar 2006-02-25, 9:54 pm |
| This is your best week of posting ever. Keep it up.
You could have stopped before you got to the grasshopper comment.
People do not impress me with their knowlege, only their competence. I
appreciate a garbage man who shows up on time, doesn't throw my cans
down the street, etc. There is a genius ophthamologist around here
that I have no respect at all for. The man is loaded with knowlege,
but is completely insane and spouts off about things beyond his scope
of knowlege. Basically, the man actually believes he is Jesus Christ.
I am not making this up.. the man is a complete whack job in the
head.. but also a genius.
Confusious say "Grasshopper, let us try and be competent at what we do
- whatever that is."
We know you have the knowlege Minarik. Your judgement and
personality need to be worked on.
On 23 Feb 2006 17:50:23 -0800, "doctor_my_eye@msn.com"
<doctor_my_eye@msn.com> wrote:
>There are opticians who have been making glasses for 30 years, but they
>have simply "learned the cookbook" and they can transpose and convert
>prescriptions effortlessly. But, they often can't imagine what the
>numbers actually mean. Hence, this attempt to turn the numbers into 3
>dimensional thought. Snatch the pebble from my hand, grasshopper. ;)
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