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| Author |
Standard quality of eyeglasses perscription question
|
|
|
| I have an O.D. who gave me an eye test and never left the 20/20 size line on
the chart. For distance, one of my eyes is blurred with his prescription,
relative to the other. Should I expect a prescription that gives me
symmetrical vision quality for both eyes, if this is possible? If I can see
the 20/20 line clearly with one eye, and struggle to guess correctly when
using the other, do I see at least 20/20 in the second eye? Or is 20/20
seeing clearly the 20/20 line?
| |
| neil0502 2004-10-31, 7:11 pm |
| Reece wrote:
> I have an O.D. who gave me an eye test and never left the 20/20 size
> line on the chart. For distance, one of my eyes is blurred with his
> prescription, relative to the other. Should I expect a prescription
> that gives me symmetrical vision quality for both eyes, if this is
> possible? If I can see the 20/20 line clearly with one eye, and
> struggle to guess correctly when using the other, do I see at least
> 20/20 in the second eye? Or is 20/20 seeing clearly the 20/20 line?
You should go back to the optometrist and voice your concern. He can verify
that the glasses were made to the accurate prescription and re-check your
vision.
| |
|
|
I believe my optometrist has bad quality control methods, and wonder if he
was taking a shortcut. The prescription he gave me he originally pulled
from a previous pair of glasses I had. Then he gave me an exam, and later
told me that the prescription had not changed. And it is this old
prescription that he says is the same as the new prescription. He has
rechecked my vision. But only to the 20/20 line on the chart. There is a
longer story that I am not going to flesh out here that includes him not
checking a new pair of glasses to see if a prescription was accurate, when
this was clearly indicated. And after a lot of expense and time spent, he
then checked, and discovered that a prescription was not accurate. But I
only want the answer to my question as phrased, or an understanding that I
may be missing.
"neil0502" <neil0502@yahoo.com> wrote in message
news:FDahd.37054$QJ3.29538@newssvr21.news.prodigy.com...
> Reece wrote:
>
> You should go back to the optometrist and voice your concern. He can
> verify
> that the glasses were made to the accurate prescription and re-check your
> vision.
>
>
| |
| Otis Brown 2004-10-31, 10:08 pm |
| "Reece" <neweducation@yahoo.com> wrote in message news:<tZahd.1483$p74.203@newssvr16.news.prodigy.com>...
Dear Reece,
You are presenting a mystery here.
The standard approach is to place you in a chair and
read the eye-chart through a "phoropter".
The OD simply changes lens power (and astigmatism)
until you read the 20/20 line. (None of this
relies on any previous prescription -- I do not
know why you state this as an issue.)
If he can not bring your eyes "up" to 20/20 by this
process -- he needs to explain that he could not do
it, and attempt to find our why. At the very
least, he needs to explain what he is doing.
It is not clear what he might have said. I would
return to him and ask him about this issue -- and
he will work to satisfy you with 20/20 in both eyes
as you request.
If not, please post here and we will help you.
Best,
Otis
(I am not an OD)
[vbcol=seagreen]
> I believe my optometrist has bad quality control methods, and wonder if he
> was taking a shortcut. The prescription he gave me he originally pulled
> from a previous pair of glasses I had. Then he gave me an exam, and later
> told me that the prescription had not changed. And it is this old
> prescription that he says is the same as the new prescription. He has
> rechecked my vision. But only to the 20/20 line on the chart. There is a
> longer story that I am not going to flesh out here that includes him not
> checking a new pair of glasses to see if a prescription was accurate, when
> this was clearly indicated. And after a lot of expense and time spent, he
> then checked, and discovered that a prescription was not accurate. But I
> only want the answer to my question as phrased, or an understanding that I
> may be missing.
>
> "neil0502" <neil0502@yahoo.com> wrote in message
> news:FDahd.37054$QJ3.29538@newssvr21.news.prodigy.com...
| |
| Reece 2004-10-31, 10:08 pm |
| Otis,
Thank you for your reply.
He did pull the prescription from my glasses before he gave me the exam. I
do not recall him working his way up from bad to good, but rather that he
started out at pretty good, as far as changing the lenses goes. If this
indeed happened, and one lens was corrected to better than 20/20 to start
out with, and then he found that I could read the 20/20 line with the other
original lenses, and went the original prescription, then there would be a
lack of symmetry in visual quality between my eyes.
To jump ahead, I had him check a pair of glasses that he prescribed, and he
said they were fine, that I could read 20/20 with them, and I insisted that
one eye was blurry, in spite of being able to read the 20/20 line. Then I
noticed that the background was a bit darker as well, when I looked at the
20/20 line of the chart. Suddenly he decided to check the glasses, though
on a previous visit he declined to do so with same complaint of blurriness.
He determined that the lab had made an error in filling the lens
prescription, by over 5 degrees, on the astigmatism. And yet I was
supposedly seeing 20/20.
So all of my original questions remain.
Reece
"Otis Brown" <otisbrown@pa.net> wrote in message
news:6dbddb9.0410311803.4320876d@posting.google.com...[vbcol=seagreen]
> "Reece" <neweducation@yahoo.com> wrote in message
> news:<tZahd.1483$p74.203@newssvr16.news.prodigy.com>...
>
> Dear Reece,
>
> You are presenting a mystery here.
>
> The standard approach is to place you in a chair and
> read the eye-chart through a "phoropter".
>
> The OD simply changes lens power (and astigmatism)
> until you read the 20/20 line. (None of this
> relies on any previous prescription -- I do not
> know why you state this as an issue.)
>
> If he can not bring your eyes "up" to 20/20 by this
> process -- he needs to explain that he could not do
> it, and attempt to find our why. At the very
> least, he needs to explain what he is doing.
>
> It is not clear what he might have said. I would
> return to him and ask him about this issue -- and
> he will work to satisfy you with 20/20 in both eyes
> as you request.
>
> If not, please post here and we will help you.
>
> Best,
>
> Otis
> (I am not an OD)
>
>
>
>
| |
|
| If you don't trust your optometrist, why not find a new one? Why would you
keep going back to someone who you don't trust or believe?
"Reece" <neweducation@yahoo.com> wrote in message
news:tZahd.1483$p74.203@newssvr16.news.prodigy.com...
>
> I believe my optometrist has bad quality control methods, and wonder if he
> was taking a shortcut. The prescription he gave me he originally pulled
> from a previous pair of glasses I had. Then he gave me an exam, and later
> told me that the prescription had not changed. And it is this old
> prescription that he says is the same as the new prescription. He has
> rechecked my vision. But only to the 20/20 line on the chart. There is a
> longer story that I am not going to flesh out here that includes him not
> checking a new pair of glasses to see if a prescription was accurate, when
> this was clearly indicated. And after a lot of expense and time spent, he
> then checked, and discovered that a prescription was not accurate. But I
> only want the answer to my question as phrased, or an understanding that I
> may be missing.
>
> "neil0502" <neil0502@yahoo.com> wrote in message
> news:FDahd.37054$QJ3.29538@newssvr21.news.prodigy.com...
>
>
| |
| Reece 2004-11-01, 11:09 am |
|
There is a pair of glasses that I have to go back for that I paid for that
is a factor in why I am asking these questions here. A new lens costs over
$150. I will not use that optometrist in the future, rest assured of that.
It is too bad you can't answer any of my original questions.
Reece
"Dana" <echo1@mail.com> wrote in message
news:1099315718.785632@netrek.net...
> If you don't trust your optometrist, why not find a new one? Why would
> you keep going back to someone who you don't trust or believe?
>
>
>
>
> "Reece" <neweducation@yahoo.com> wrote in message
> news:tZahd.1483$p74.203@newssvr16.news.prodigy.com...
>
>
>
| |
| Robert Martellaro 2004-11-01, 7:12 pm |
| On Sun, 31 Oct 2004 18:49:40 GMT, "Reece" <neweducation@yahoo.com> wrote:
>I have an O.D. who gave me an eye test and never left the 20/20 size line on
>the chart. For distance, one of my eyes is blurred with his prescription,
>relative to the other. Should I expect a prescription that gives me
>symmetrical vision quality for both eyes,
Yes, excluding pathology and refractive anomalies like irregular astigmatism.
What's your age, Rx, and lens design (single vision, multifocal)
>if this is possible?
Impossible to say because of the above.
> If I can see
>the 20/20 line clearly with one eye, and struggle to guess correctly when
>using the other, do I see at least 20/20 in the second eye? Or is 20/20
>seeing clearly the 20/20 line?
>
If you get every letter correct you're 20/20. If you miss a letter your 20/20
-1. You could have double vision or loss of contrast and still see 20/20. The
Snellen eye chart is not always the last word in determining how well you see.
By the way, there are more lines below the 20/20 line, for instance I see
20/15-1 with both eyes corrected.
Hope this helps
Robert Martellaro
~~~~~~~~~~~~~~~~~~
Optician/Owner
Roberts Optical
robopt@execpc.com
~~~~~~~~~~~~~~~~~~
"Science is a way of trying not to fool yourself."
- Richard Feynman
| |
|
| Thanks Robert.
No known pathologies or anomalies.
Age: 48
Single vision
___ sph cyl Axis
od -3.50 -1.50 017
os -3.50 -1.25 167
I would have preferred my optometrist have gone to the 20/15 line to
determine that my eyes were not corrected to vision of equal quality.
So, with that information, what can we conclude? Should I have to specially
ask to have equal quality of vision in both eyes? Or is merely ensuring
that each eye is 20/20 corrected a job within standards, without regard to
symmetry in vision quality?
Thanks,
Reece
"Robert Martellaro" <robopt@nospam.com> wrote in message
news:8gpco09g1ppko7ovg0ld6ov7o2hgm7e5df@4ax.com...
> On Sun, 31 Oct 2004 18:49:40 GMT, "Reece" <neweducation@yahoo.com> wrote:
>
>
> Yes, excluding pathology and refractive anomalies like irregular
> astigmatism.
> What's your age, Rx, and lens design (single vision, multifocal)
>
>
> Impossible to say because of the above.
>
>
> If you get every letter correct you're 20/20. If you miss a letter your
> 20/20
> -1. You could have double vision or loss of contrast and still see
> 20/20. The
> Snellen eye chart is not always the last word in determining how well you
> see.
> By the way, there are more lines below the 20/20 line, for instance I see
> 20/15-1 with both eyes corrected.
>
> Hope this helps
>
>
>
>
>
> Robert Martellaro
> ~~~~~~~~~~~~~~~~~~
> Optician/Owner
> Roberts Optical
> robopt@execpc.com
> ~~~~~~~~~~~~~~~~~~
> "Science is a way of trying not to fool yourself."
> - Richard Feynman
| |
| Robert Martellaro 2004-11-01, 7:12 pm |
| On Mon, 01 Nov 2004 18:47:36 GMT, "Reece" <neweducation@yahoo.com> wrote:
>Thanks Robert.
>
>No known pathologies or anomalies.
>Age: 48
>Single vision
>___ sph cyl Axis
>od -3.50 -1.50 017
>os -3.50 -1.25 167
>
>I would have preferred my optometrist have gone to the 20/15 line to
>determine that my eyes were not corrected to vision of equal quality.
>
>So, with that information, what can we conclude? Should I have to specially
>ask to have equal quality of vision in both eyes? Or is merely ensuring
>that each eye is 20/20 corrected a job within standards, without regard to
>symmetry in vision quality?
>
>Thanks,
>
>Reece
Reece,
No, you do not have to request that the Rx provides optimal vision and comfort
for "both" eyes. Either someone dropped the ball or there is some inherent
problem with one of the eyes that can not be corrected with eyeglass lenses, the
lenses are fit and/or and fabricated improperly, you are pseudomyopic in one
eye, one eye was purposely overplused to assist with the near vision etc.
Hope this helps
Robert Martellaro
~~~~~~~~~~~~~~~~~~
Optician/Owner
Roberts Optical
robopt@execpc.com
~~~~~~~~~~~~~~~~~~
"Science is a way of trying not to fool yourself."
- Richard Feynman
| |
| Dan Abel 2004-11-01, 7:12 pm |
| In article <6dbddb9.0410311803.4320876d@posting.google.com>,
otisbrown@pa.net (Otis Brown) wrote:
> "Reece" <neweducation@yahoo.com> wrote in message
news:<tZahd.1483$p74.203@newssvr16.news.prodigy.com>...
> The OD simply changes lens power (and astigmatism)
> until you read the 20/20 line. (None of this
> relies on any previous prescription -- I do not
> know why you state this as an issue.)
I'm no OD, but I know they like to start with the old prescription and
move up and down until they get best vision. This is my preference. When
I was a -10 I wouldn't have liked sitting in the chair while they started
from -1 and worked their way up to -10. That would have been a waste of
time for both of us.
--
Dan Abel
Sonoma State University
AIS
dabel@sonic.net
| |
| neil0502 2004-11-01, 7:12 pm |
| Reece wrote:
> It is too bad you can't answer any of my original questions.
I hope your optometrist finds you easier to work with than I, for one, do.
| |
|
| Thank you Robert! You have given me closure on the reason for my visit to
this newsgroup. I will now be informed in my next conversation with that
O.D. It is a tricky situation, as the O.D. is "independent" of a major
glasses retailer and at the same site as well. And so, since they are not a
single entity, it makes for a creepier transaction when things go wrong.
My abbreviated history on a single pair of glasses is this:
1. On first visit to this O.D., the Dr. looks at my glasses, does an exam,
writes a prescription. And states that my vision has changed little. To me
this means that my vision has changed, as he could not logically make this
statement based on the old prescription obtained by looking at the glasses,
if my prescription hadn't changed. (That is my opinion.)
2. I go to another branch of the major glasses retailer, as it is near a
project where I work. I immediately notice a blur in one eye. Salesperson
says that it is probably because I am tired.
3. The next day I just put on my new glasses, and indoors they seem fine. I
am working heavy hours, so I don't do a lot of tests, and never put on my
old glasses for months.
4. Believing that my prescription has changed, albeit little, I go in to the
retailer branch where the Dr. who wrote my prescription worked, to have new
sunglasses ordered. But while they are ringing it up, I notice that my new
glasses are blurry out of the same eye that was the case when I picked them
up, and so I ask them to hold my order while I make an appt. with the Dr.
that wrote the prescription. I told my Dr. about the blurriness and the
blurriness when they were first delivered, and so he gave me an exam. I
asked him if he didn't want to check glasses to get the prescription from
the glasses to see if they were correct. He declined, assuring me that the
were correct. He proceeded to examine my eyes, and based on his test, there
was what he called an insignificant change in the prescription. Changing
the Cyl. from -1.25 to -1.50. (I state these numbers from memory.) He
insisted that it was insignificant. And handed me a lens to look through
with my glasses. It clearly made a difference. Unbeknownst to me the
correction was for the left eye, and I tested the lens with my right eye.
(I had told him that it was my right eye that was seeing blurry.) So based
on this, I had a new lens ordered for my glasses with the new prescription.
5. The glasses came back, and of course the blur was still there, since the
lens had been changed for the other eye (if that!). And so finally the Dr.
looked at the glasses, and discovered that both lenses were incorrect. So
right now I am fighting for the $160 on the bogus lens change with the
retailer. But if it goes poorly there, I will fight with the O.D.'s
company.
Over the last few days I discovered that for distance, with my old glasses,
it is blurry for reading at a distance through my right eye, suggesting to
me that the same will be the case with my new glasses, whenever they call me
to pick them up. Since my new prescription for the right eye hasn't
changed, according to what the Dr. said. So I expect that the lab will have
done it to match my old glasses on the right eye, which means, that although
my right eye corrected sees 20/20, it is not close to being equal in
corrected quality to my left eye. Which means there is yet another fight.
So there is my story.
Thanks again for your input. The knowledge I have gotten from your response
and way you have discussed the issue will undoubtedly help me resolve this
mess, in a low-key way.
Reece
"Robert Martellaro" <robopt@nospam.com> wrote in message
news:eh3do09ad3v1tg5ukckag5o61puiuh75i4@4ax.com...
> On Mon, 01 Nov 2004 18:47:36 GMT, "Reece" <neweducation@yahoo.com> wrote:
>
>
> Reece,
>
> No, you do not have to request that the Rx provides optimal vision and
> comfort
> for "both" eyes. Either someone dropped the ball or there is some inherent
> problem with one of the eyes that can not be corrected with eyeglass
> lenses, the
> lenses are fit and/or and fabricated improperly, you are pseudomyopic in
> one
> eye, one eye was purposely overplused to assist with the near vision etc.
>
> Hope this helps
>
>
>
>
> Robert Martellaro
> ~~~~~~~~~~~~~~~~~~
> Optician/Owner
> Roberts Optical
> robopt@execpc.com
> ~~~~~~~~~~~~~~~~~~
> "Science is a way of trying not to fool yourself."
> - Richard Feynman
| |
|
| My optometrist has made some professional mistakes in my case. How many
mistakes is still up in the air.
While there have been some excellent responses here, some responses have
been trivial and assume that the optometrist is a good, efficient guy and
that I should just go back to the guy--as if he didn't cost me an
unnecessary bunch of money and time. This guy has made numerous mistakes.
So excuse me for trying to get some information, rather than happily
accepting suggestions that I go to the optometrist who is the source of my
problems.
"neil0502" <neil0502@yahoo.com> wrote in message
news:Scxhd.37525$QJ3.3910@newssvr21.news.prodigy.com...
> Reece wrote:
>
>
> I hope your optometrist finds you easier to work with than I, for one, do.
>
>
| |
| neil0502 2004-11-01, 7:12 pm |
| Reece wrote:
It is too bad you can't answer any of my original questions.
neil0502 wrote:
I hope your optometrist finds you easier to work with than I, for
one, do.
Reece wrote:
> My optometrist has made some professional mistakes in my case. How
> many mistakes is still up in the air.
>
> While there have been some excellent responses here, some responses
> have been trivial and assume that the optometrist is a good,
> efficient guy and that I should just go back to the guy--as if he
> didn't cost me an unnecessary bunch of money and time. This guy has
> made numerous mistakes. So excuse me for trying to get some
> information, rather than happily accepting suggestions that I go to
> the optometrist who is the source of my problems.
I will happiliy excuse you for 'trying to get information.' What I'm
calling you on is being petulant toward people who were trying to help you
in the best way they could. May I suggest a simple "Thanks," or, "Excellent
suggestion, but do you also know whether equal vision in both eyes should be
expected?" or even . . . no reply at all if you didn't get the info you
wanted? The information you provided us in your original post--as it turns
out--was inadequate to give you a very precise response.
I don't mean to come across too strongly. This is e-mail and all tone is
absent. I'm just suggesting that your response was a bit sarcastic and
unnecessary . . . for future reference.
| |
|
| Thanks.
That is fair. I will keep that in mind. Thanks for being a mirror to show
me what I could not otherwise see.
Reece
"neil0502" <neil0502@yahoo.com> wrote in message
news:DCxhd.37527$QJ3.31076@newssvr21.news.prodigy.com...
> Reece wrote:
>
> It is too bad you can't answer any of my original questions.
>
> neil0502 wrote:
>
> I hope your optometrist finds you easier to work with than I, for
> one, do.
>
> Reece wrote:
>
>
> I will happiliy excuse you for 'trying to get information.' What I'm
> calling you on is being petulant toward people who were trying to help you
> in the best way they could. May I suggest a simple "Thanks," or,
> "Excellent
> suggestion, but do you also know whether equal vision in both eyes should
> be
> expected?" or even . . . no reply at all if you didn't get the info you
> wanted? The information you provided us in your original post--as it
> turns
> out--was inadequate to give you a very precise response.
>
> I don't mean to come across too strongly. This is e-mail and all tone is
> absent. I'm just suggesting that your response was a bit sarcastic and
> unnecessary . . . for future reference.
>
>
| |
| neil0502 2004-11-01, 7:12 pm |
| Reece wrote:[vbcol=seagreen]
> Thanks.
>
> That is fair. I will keep that in mind. Thanks for being a mirror
> to show me what I could not otherwise see.
>
> Reece
>
> "neil0502" <neil0502@yahoo.com> wrote in message
> news:DCxhd.37527$QJ3.31076@newssvr21.news.prodigy.com...
You are a gentleman and a scholar. Best of luck with your optometrist.
Please let the newsgroup know how it turns out!
| |
| Mike Tyner 2004-11-01, 7:12 pm |
|
"Reece" <neweducation@yahoo.com> wrote
> So, with that information, what can we conclude? Should I have to
> specially ask to have equal quality of vision in both eyes? Or is merely
> ensuring that each eye is 20/20 corrected a job within standards, without
> regard to symmetry in vision quality?
You should expect equal acuity unless one eye has pathology that limits the
best result.
As to 20/20 vs 20/15, that's valid for testing the outcome, but the lens
that makes the 20/20 line sharpest (eg -350 in your case) is the same as the
lens that makes the 20/15 line sharpest. IOW, which line you use is not as
important as which lens you choose. Fine discriminations in focus ("1 or 2")
may be somewhat easier with the 20/15 line than say, the 20/50 line. When he
gets done, and get both eyes balanced, then it's the time to pull up the
20/15 (or 20/10) line.
-MT
| |
| Reece 2004-11-01, 10:08 pm |
| Thanks, MT. I appreciate your response.
How does an O.D. get both eyes balanced?
Reece
"Mike Tyner" <mtyner@mindspring.com> wrote in message
news:iNzhd.16500$ta5.16316@newsread3.news.atl.earthlink.net...
>
> "Reece" <neweducation@yahoo.com> wrote
>
>
> You should expect equal acuity unless one eye has pathology that limits
> the best result.
>
> As to 20/20 vs 20/15, that's valid for testing the outcome, but the lens
> that makes the 20/20 line sharpest (eg -350 in your case) is the same as
> the lens that makes the 20/15 line sharpest. IOW, which line you use is
> not as important as which lens you choose. Fine discriminations in focus
> ("1 or 2") may be somewhat easier with the 20/15 line than say, the 20/50
> line. When he gets done, and get both eyes balanced, then it's the time to
> pull up the 20/15 (or 20/10) line.
>
> -MT
>
>
| |
| Mike Tyner 2004-11-02, 2:09 am |
| "Reece" <neweducation@yahoo.com> wrote
> Thanks, MT. I appreciate your response.
>
> How does an O.D. get both eyes balanced?
There are several techniques, and each refractionist will have their own
preferences. But those who omit this step are doomed to remake a lot of
glasses. Forgive me if my explanation rambles, but I'm not sure how much of
the optics you already understand. (And IMO, your problem is not likely one
of balance.)
The object of balancing is to assure that the correction is equal for each
eye. If we simply rely on "1 or 2" with each eye alone, often you will
choose more correction than you need in one eye or the other. It isn't
anybody's fault, it's just that the endpoint is "subjective", meaning you
choose an endpoint based on your interpretation of "sharp" and on the the
semivoluntary posture of your accommodating muscles. In young people, that
often affects the result by a half diopter or more. Closing one eye is
notorious for affecting the posture of your focusing muscles.
By "endpoint" I'm referring to the final _sphere_ value; I believe yours
was -3.50 in each eye.
In my experience, it's ok to use a _monocular_ sphere value as a basis for
determining the "fine points" of astigmatism and axis, but once those fine
points are nailed down, the sphere values should be balanced so that one eye
isn't overcorrected or undercorrected relative to the other. (In myopia,
undercorrection makes things blurry, and overcorrection makes distant
objects "smaller and darker".) Either one is tolerated better if one eye
isn't out of whack with the other.
Two popular techniques for balancing are 1) equalizing fog and 2) chromatic
interval. Each of these techniques has numerous variations and accompanying
pitfalls.
I use the first technique most often. Once the (tentative) cylinder and axis
are determined, I would reduce both eyes to -3.00 sphere and alternate my
hand over each eye, asking which is clearer. The object here is to make the
small letters _equally blurry_ in order to equalize the relationship between
the two eyes. If the left eye is clearer, I'd reduce it to -2.75 in order
to achieve equal blur. If they weren't equal then, but instead better in the
_right_ eye, I'd try to minimize the difference, making them as equal as
possible, to the nearest 025.
Once the blur is equalized, we uncover both eyes and do "1 or 2"
binocularly, on the presumption that binocular vision is more natural and
relaxed than monocular and a little less prone to overaccommodation.
The final binocular endpoint is determined when a) one notch less minus is
blurry and b) one notch more doesn't help. In young people, one notch more
than they need (eg -375 for you) would look smaller and darker and it's
seductive. But we know it's excessive, if dropping back to -350 doesn't
create blur at the bottom of the chart. -325 _should_ be perceptibly
blurry. -350 and -375 should look much the same. This is why it doesn't
matter much _which line_ you use. _All_ of the lines are a little blurry
at -325, but it's easier to detect with smaller letters.
Now for the pitfall of this technique. Once the balance is achieved and the
final sphere values are determined, we expect each eye to be equally sharp
at the bottom of the snellen chart. If one eye is blurry, then a) the
cylinder or axis are off in the blurry eye or b) the blurry eye has some
pathology that prevents it from matching the better eye. In either case, the
relative blur technique will tend to over-minus the blurry eye. If we cover
the _better_ eye, we find that 1 or 2 or 3 notches less minus don't increase
the blur. That's a sure sign that there's something wrong and we better
check the "fine points" again. With experience, the "pitfall" becomes a
useful screening method for finding pathology and spotting bad refractions.
A second balancing technique uses the "chromatic interval". Different colors
refract differently, the same principle that creates Newton's ROYGBIV
rainbow with a handheld prism. With ophthalmic lenses, you can think of blue
light focusing before red light - for a given white object at infinity, blue
focuses in front of the retina and red behind. Since black letters are hard
to see on a BLUE background, we use GREEN and red for this technique. A
chart is presented with red background on one side and green on the other.
Each eye is tested alone. We start with too little minus (eg -300) and
gradually add minus, quarter by quarter. Initially the RED side looks more
focused than the GREEN side. As more minus is added, at some point the GREEN
side becomes better focused, and that's usually considered the endpoint.
After repeating for the other eye, we have some assurance that each eye is
equally corrected, so then we remove the red and green, open both eyes, and
adjust the sphere value binocularly (both eyes simultaneous) for the final
binocular endpoint.
It sounds complicated, but it really goes very quickly if you know what
you're doing. At the end of the process, if one eye is better than the
other, there is either a mistake in the astigmatism correction, or pathology
in one eye. Unlike the first technique, R-G balancing doesn't tend to
over-minus the "bad" eye.
-MT
"Reece" <neweducation@yahoo.com> wrote in message
news:_yBhd.18788$5b1.5170@newssvr17.news.prodigy.com...
> Thanks, MT. I appreciate your response.
>
> How does an O.D. get both eyes balanced?
>
> Reece
>
>
> "Mike Tyner" <mtyner@mindspring.com> wrote in message
> news:iNzhd.16500$ta5.16316@newsread3.news.atl.earthlink.net...
>
>
| |
|
| Thank you very much for your detailed reply, Mike!
In my case, I don't believe my Dr. did any balancing. But I think that your
statement that closing one eye affects the posture of your focusing muscles
is important in my case. And maybe that is my whole issue with my old
glasses--which my new glasses that are being corrected will pretty much
match. I have run tests on myself this afternoon, and I observed that
sometimes I can read the 20/15 line with either eye (I printed a chart
out)--especially if I focus using both first and then just cover one eye or
the other (with a very bright light on the chart). It also seems to work
better if I do not completely cover the eye that is not looking at the
chart. This perfectly dovetails with the posture of my focusing muscles
issue when closing an eye.
On Saturday, I had a bit of trouble seeing text on distant signs clearly
with my left eye when I was driving, compared to my right eye, using the
cover-an-eye method. So, perhaps my left eye knows how to posture solo
better than my right. My right eye has lived with an astigmatism correction
that was off by 6 degrees from May to September, so perhaps it got lazy (if
eyes can get lazy that way).
So I will pick up my glasses on the morning after they call me, when my eyes
are fresh and the sun is out, and will focus with both eyes when I go
outside of the place, and then close one eye or the other for testing on
distant signs.
Thanks again!
Reece
"Mike Tyner" <mtyner@mindspring.com> wrote in message
news:haFhd.16806$ta5.8803@newsread3.news.atl.earthlink.net...
> "Reece" <neweducation@yahoo.com> wrote
>
>
> There are several techniques, and each refractionist will have their own
> preferences. But those who omit this step are doomed to remake a lot of
> glasses. Forgive me if my explanation rambles, but I'm not sure how much
> of the optics you already understand. (And IMO, your problem is not likely
> one of balance.)
>
> The object of balancing is to assure that the correction is equal for each
> eye. If we simply rely on "1 or 2" with each eye alone, often you will
> choose more correction than you need in one eye or the other. It isn't
> anybody's fault, it's just that the endpoint is "subjective", meaning you
> choose an endpoint based on your interpretation of "sharp" and on the the
> semivoluntary posture of your accommodating muscles. In young people, that
> often affects the result by a half diopter or more. Closing one eye is
> notorious for affecting the posture of your focusing muscles.
>
> By "endpoint" I'm referring to the final _sphere_ value; I believe yours
> was -3.50 in each eye.
>
> In my experience, it's ok to use a _monocular_ sphere value as a basis for
> determining the "fine points" of astigmatism and axis, but once those fine
> points are nailed down, the sphere values should be balanced so that one
> eye isn't overcorrected or undercorrected relative to the other. (In
> myopia, undercorrection makes things blurry, and overcorrection makes
> distant objects "smaller and darker".) Either one is tolerated better if
> one eye isn't out of whack with the other.
>
> Two popular techniques for balancing are 1) equalizing fog and 2)
> chromatic interval. Each of these techniques has numerous variations and
> accompanying pitfalls.
>
> I use the first technique most often. Once the (tentative) cylinder and
> axis are determined, I would reduce both eyes to -3.00 sphere and
> alternate my hand over each eye, asking which is clearer. The object here
> is to make the small letters _equally blurry_ in order to equalize the
> relationship between the two eyes. If the left eye is clearer, I'd reduce
> it to -2.75 in order to achieve equal blur. If they weren't equal then,
> but instead better in the _right_ eye, I'd try to minimize the difference,
> making them as equal as possible, to the nearest 025.
>
> Once the blur is equalized, we uncover both eyes and do "1 or 2"
> binocularly, on the presumption that binocular vision is more natural and
> relaxed than monocular and a little less prone to overaccommodation.
>
> The final binocular endpoint is determined when a) one notch less minus is
> blurry and b) one notch more doesn't help. In young people, one notch more
> than they need (eg -375 for you) would look smaller and darker and it's
> seductive. But we know it's excessive, if dropping back to -350 doesn't
> create blur at the bottom of the chart. -325 _should_ be perceptibly
> blurry. -350 and -375 should look much the same. This is why it doesn't
> matter much _which line_ you use. _All_ of the lines are a little blurry
> at -325, but it's easier to detect with smaller letters.
>
> Now for the pitfall of this technique. Once the balance is achieved and
> the final sphere values are determined, we expect each eye to be equally
> sharp at the bottom of the snellen chart. If one eye is blurry, then a)
> the cylinder or axis are off in the blurry eye or b) the blurry eye has
> some pathology that prevents it from matching the better eye. In either
> case, the relative blur technique will tend to over-minus the blurry eye.
> If we cover the _better_ eye, we find that 1 or 2 or 3 notches less minus
> don't increase the blur. That's a sure sign that there's something wrong
> and we better check the "fine points" again. With experience, the
> "pitfall" becomes a useful screening method for finding pathology and
> spotting bad refractions.
>
> A second balancing technique uses the "chromatic interval". Different
> colors refract differently, the same principle that creates Newton's
> ROYGBIV rainbow with a handheld prism. With ophthalmic lenses, you can
> think of blue light focusing before red light - for a given white object
> at infinity, blue focuses in front of the retina and red behind. Since
> black letters are hard to see on a BLUE background, we use GREEN and red
> for this technique. A chart is presented with red background on one side
> and green on the other. Each eye is tested alone. We start with too little
> minus (eg -300) and gradually add minus, quarter by quarter. Initially the
> RED side looks more focused than the GREEN side. As more minus is added,
> at some point the GREEN side becomes better focused, and that's usually
> considered the endpoint. After repeating for the other eye, we have some
> assurance that each eye is equally corrected, so then we remove the red
> and green, open both eyes, and adjust the sphere value binocularly (both
> eyes simultaneous) for the final binocular endpoint.
>
> It sounds complicated, but it really goes very quickly if you know what
> you're doing. At the end of the process, if one eye is better than the
> other, there is either a mistake in the astigmatism correction, or
> pathology in one eye. Unlike the first technique, R-G balancing doesn't
> tend to over-minus the "bad" eye.
>
> -MT
>
>
> "Reece" <neweducation@yahoo.com> wrote in message
> news:_yBhd.18788$5b1.5170@newssvr17.news.prodigy.com...
>
>
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