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Science Forum Index » Medicine - Vision Forum » accuracy of measuring lenses
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| denaman@hotmail.com |
 Posted: Thu Feb 01, 2007 8:36 pm |
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Say, how accurate is it when Lenscrafters takes your existing pair of
glasses, takes them back in the lab, and measures the lenses? Are
they able to precisely read your existing prescription, or is there a
lot of variation?
The reason I ask is because they did precisely this and came up with a
-6.50 reading on one lens (I'll keep it to the one lens to keep it
simple), whereas I believe all my prescriptions are higher than that,
but can not be sure because perhaps I've misplaced one. And I don't
know which paper prescription belongs to these lenses.
One more question. As you go from say -6.50 to -7.00 to -8.00, are
these marginal jumps perceptually. By that I mean if I go from one to
the next would the prescription be just a hair better or is it a stark
difference?
I have a case where I'm perfectly happy with my current prescription,
which Lenscrafters is saying is -6.50. Went to the eye doctor last
month and got my eyes checked and she said that my right eye is
-8.00. Now I don't want a pair of binoculars strapped to my head if I
don't need them; I really don't need to see the cracks in the paint on
the house across the street. So, I was going to go with a six year
old prescription that gave a lower reading of -7.00. That was why I
was interested in my existing prescription; I wouldn't want to go
backwards and spend all that money on a worse prescription. |
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| Dan Abel |
| Posted: Thu Feb 01, 2007 9:13 pm |
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In article <1170376599.594777.198000@l53g2000cwa.googlegroups.com>,
"denaman@hotmail.com" <denaman@hotmail.com> wrote:
Quote: Say, how accurate is it when Lenscrafters takes your existing pair of
glasses, takes them back in the lab, and measures the lenses? Are
they able to precisely read your existing prescription, or is there a
lot of variation?
Last time I tried this, it didn't work too well. I'd recommend an exam.
Quote: The reason I ask is because they did precisely this and came up with a
-6.50 reading on one lens (I'll keep it to the one lens to keep it
simple), whereas I believe all my prescriptions are higher than that,
but can not be sure because perhaps I've misplaced one. And I don't
know which paper prescription belongs to these lenses.
Call the doctor's office. They should have records.
Quote: One more question. As you go from say -6.50 to -7.00 to -8.00, are
these marginal jumps perceptually. By that I mean if I go from one to
the next would the prescription be just a hair better or is it a stark
difference?
There's a difference. Some people are OK with it and some aren't.
Quote: I have a case where I'm perfectly happy with my current prescription,
which Lenscrafters is saying is -6.50. Went to the eye doctor last
month and got my eyes checked and she said that my right eye is
-8.00. Now I don't want a pair of binoculars strapped to my head if I
don't need them; I really don't need to see the cracks in the paint on
the house across the street. So, I was going to go with a six year
old prescription that gave a lower reading of -7.00. That was why I
was interested in my existing prescription; I wouldn't want to go
backwards and spend all that money on a worse prescription.
The doctor gets money for determining the best prescription. I think
it's negotiable. |
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| Bucky |
| Posted: Fri Feb 02, 2007 3:05 am |
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On Feb 1, 4:36 pm, "dena...@hotmail.com" <dena...@hotmail.com> wrote:
Quote: Say, how accurate is it when Lenscrafters takes your existing pair of
glasses, takes them back in the lab, and measures the lenses? Are
they able to precisely read your existing prescription, or is there a
lot of variation?
they're not that accurate.
Quote: I have a case where I'm perfectly happy with my current prescription,
which Lenscrafters is saying is -6.50.
if you can see 20/20 at -6.50 without eyestrain, then stick with it. |
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| Dom |
| Posted: Fri Feb 02, 2007 8:28 am |
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denaman@hotmail.com wrote:
Quote: Say, how accurate is it when Lenscrafters takes your existing pair of
glasses, takes them back in the lab, and measures the lenses? Are
they able to precisely read your existing prescription, or is there a
lot of variation?
The reason I ask is because they did precisely this and came up with a
-6.50 reading on one lens (I'll keep it to the one lens to keep it
simple), whereas I believe all my prescriptions are higher than that,
but can not be sure because perhaps I've misplaced one. And I don't
know which paper prescription belongs to these lenses.
One more question. As you go from say -6.50 to -7.00 to -8.00, are
these marginal jumps perceptually. By that I mean if I go from one to
the next would the prescription be just a hair better or is it a stark
difference?
I have a case where I'm perfectly happy with my current prescription,
which Lenscrafters is saying is -6.50. Went to the eye doctor last
month and got my eyes checked and she said that my right eye is
-8.00. Now I don't want a pair of binoculars strapped to my head if I
don't need them; I really don't need to see the cracks in the paint on
the house across the street. So, I was going to go with a six year
old prescription that gave a lower reading of -7.00. That was why I
was interested in my existing prescription; I wouldn't want to go
backwards and spend all that money on a worse prescription.
There can be a margin of error, but you wouldn't expect it to be more
than about 0.25 dioptres at -6.50. This probably correlates pretty well
with the jnd (just noticeable difference) during refraction for most
patients with this degree of myopia.
This leads to the answer to your second question: a change of 0.50
dioptres should for most people be quite obviously noticeable... UNTIL
you reach your correct refraction, after which further increases will
probably look different but not clearer.
At these higher powers the frame fitting (i.e. distance from eyes, and
angle of lenses to face) and lens type (i.e.
index/asphericity/material) starts to become more important than 0.25
dioptres here or there.
Dom |
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| denaman@hotmail.com |
| Posted: Fri Feb 02, 2007 2:07 pm |
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