Difference between these prescriptions?

Hello,

I was wondering what the difference between these two prescriptions
is. They are my mom's. The first one is from last year, and those are
the glasses she is currently wearing and can see reasonably well
from.

The second one is new. She ordered glasses from Zenni and says she
can't see well in the left eye. I had the glasses checked at two
opticians' offices and they both said that the prescription is "pretty
accurate". They both said the axis may be off a bit, but should be
unnoticeable. I suspect her new eye doctor may have given her a
prescription that may be wrong for her. (Notes: Lenses are
progressive bifocals. And she can see much better from her old
lenses.)

Last year...

OD:
Sphere: +2.75
Cylinder: -0.75
Axis: 095

OS:
Sphere: +3.25
Cylinder: -1.25
Axis: 105

This year...

OD:
Sphere: +2.00
Cylinder: +0.75
Axis: 180

OS:
Sphere: +1.50
Cylinder: +1.00
Axis: 025

Thanks!!!

Ed

"Salmon Egg" <(E-Mail Removed)> wrote in message
news:SalmonEgg-(E-Mail Removed)...
> You do not have to be a vision professional (I am not) to figure out
> that there is very little difference between the two prescriptions. What
> difference there is, is easy to attribute to small measurement error. My
> guess is that you went to two different practitioners, Not only that,
> but I would not be surprised if one was an optometrist while the other
> was an ophthalmologist.
>
> A given spectacle lens with astigmatism correction does not have a
> unique prescription. Two equal power cylindrical lenses crossed at right
> angles form the equivalent of a spherical lens. The practitioner can use
> one of two ways to describe the lens. You have an example of both ways.
>
> As an example, I will use your first lens prescription.
>
> Add Compensate with Net
> Original Sphere crossed cylinders
> Sphere: +2.75 -0.75 +2.00
> Cylinder: -0.75 +0.75 +0.75 +0.75
> Axis: 095 095 195 195
>
> That is, a spherical lens is added and then subtracted in the form of
> two crossed cylindrical lenses. The result is very close to your second
> prescription.
>
> I have been on a bit of a soapbox suggesting that Zernicke functions be
> used for prescriptions. Then there would be a unique way of prescribing
> a lens. As it becomes economically feasible to manufacture aspheric
> lenses, it may become feasible to correct astigmatism with such lenses
> rather than easier to fabricate cylindrical lenses.
>
> It is interesting to note that the popularity of refractive surgery is
> making the use of Zernicke functions part of what the surgeons know,
> Nevertheless, I doubt than mainstream prescribing will change during my
> lifetime.
>
> Bill

To translate the above in plain English:

There are two ways to express a correction for astigmatism, one with a minus
correction and the other with a plus. If an Rx uses a plus cylinder, then
the sphere must also be changed if it is compared to an Rx with a minus
cylinder. The net is that both Rx's are very close to each other if the
adjustment for the plus cylinder is made.

As noted, most plus cylinder Rx are written by ophthalmologists, who have a
chip on their shoulder and want to feel superior to an optometrist who will
usually use a minus cylinder. You do not need to get an Rx for glasses or
contacts from an ophthalmologist unless you have some sort of eye disease or
serous problem with your eyes (other than just needing correction).

Wouldn't a 90-degree change in the axis be rather noticeable? Isn't
that what she's got here?

Liz
Indy
USA

On Nov 30, 10:39*pm, Ed <edutital...@yahoo.com> wrote:
> Hello,
>
>
> The second one is new. She ordered glasses from Zenni and says she
> can't see well in the left eye. I had the glasses checked at two
> opticians' offices and they both said that the prescription is "pretty
> accurate". They both said the axis may be off a bit, but should be
> unnoticeable. I suspect her new eye doctor may have given her a
> prescription that may be wrong for her. *(Notes: Lenses are
> progressive bifocals. And she can see much better from her old
> lenses.)

The prescriptions are very similar, one is in plus cyl form, the other
in minus cyl form so they look different.

Did she order the same brand of progressive and same material as the
old pair? Progressives vary greatly in quality. The problem is
likely to be centration of the lenses and adjustment of the frame.
Progressives are very sensitive to placement, being 1 mm out will
cause problems. And if the frame is not angled correctly they don't
work well either.

A major problem with Internet ordering of progressives -- how do you
get accurate measures and a good frame adjustment?

Dr Judy

In article
<328bb144-5d1b-4f4f-ac59-(E-Mail Removed)>,
Liz <(E-Mail Removed)> wrote:

> Wouldn't a 90-degree change in the axis be rather noticeable? Isn't
> that what she's got here?

I don't pretend to understand why, but plus readings are always 90
degrees off from minus readings.

--
Dan Abel
Petaluma, California USA
(E-Mail Removed)

In article <SalmonEgg-(E-Mail Removed)>,
Salmon Egg <(E-Mail Removed)> wrote:

> In article
> <dabel-(E-Mail Removed)>,
> Dan Abel <(E-Mail Removed)> wrote:
>
> > In article
> > <328bb144-5d1b-4f4f-ac59-(E-Mail Removed)>,
> > Liz <(E-Mail Removed)> wrote:
> >
> > > Wouldn't a 90-degree change in the axis be rather noticeable? Isn't
> > > that what she's got here?
> >
> > I don't pretend to understand why, but plus readings are always 90
> > degrees off from minus readings.
>
> Only if you are describing the same lens in two different ways.

Well, obviously there must be some lenses inside of those gizmos, but we
aren't talking about lenses, but about comparing prescriptions. If the
diopters for cylinders is plus, then the degrees will be different by 90
for the same prescription where the cylinders is minus.

--
Dan Abel
Petaluma, California USA
(E-Mail Removed)

On Dec 3, 7:34*pm, Liz <fraternobom...@yahoo.com> wrote:
> Wouldn't a 90-degree change in the axis be rather noticeable? * *Isn't
> that what she's got here?

The axis changes depending on whether plus or minus cyl form. Cyl
form is a shorthand for the full prescription.

For example, full prescription is

+2.00 along 180 axis with +3.00 along the 090 axis

This can be written as
+3.00 -1.00 x 180 (+3.00 along 90, subtract 1.00 dioptre from the 180)
or
+2.00 +1.00 x 90 (+2.00 along 180, add 1.00 to the 90)

All three prescriptions specify exactly the same lens.

Judy

On Dec 3, 9:08*pm, Salmon Egg <Salmon...@sbcglobal.net> wrote:
> In article
> <9d7ea9af-c18f-4a1c-bd23-b16246f7f...@31g2000vbf.googlegroups.com>,
> *Dr Judy <mpac...@rogers.com> wrote:
>
> > Did she order the same brand of progressive and same material as the
> > old pair? * Progressives vary greatly in quality. *The problem is
> > likely to be centration of the lenses and adjustment of the frame.
> > Progressives are very sensitive to placement, being 1 mm out will
> > cause problems. *And if the frame is not angled correctly they don't
> > work well either.
>
> Do you really mean "vary greatly in quality" or just in design?

Both, but mostly design. Some older (and cheaper) designs have very
narrow corridors and much more distortion.



> Your mention of sensitivity to placement is why I question the utility
> of using correction other than simple sphere and astigmatism, I can
> understand that aspherics are easily hyped and can be the source of
> profit.

All progressives are aspheric. If you don't want aspheric, you must
stick with a line bifocal or trifocal


Judy

In article
<44cfa4e9-bc84-488a-8f72-(E-Mail Removed)>,
Dr Judy <(E-Mail Removed)> wrote:

> On Dec 3, 7:34*pm, Liz <fraternobom...@yahoo.com> wrote:
> > Wouldn't a 90-degree change in the axis be rather noticeable? * *Isn't
> > that what she's got here?
>
> The axis changes depending on whether plus or minus cyl form. Cyl
> form is a shorthand for the full prescription.
>
> For example, full prescription is
>
> +2.00 along 180 axis with +3.00 along the 090 axis
>
> This can be written as
> +3.00 -1.00 x 180 (+3.00 along 90, subtract 1.00 dioptre from the 180)
> or
> +2.00 +1.00 x 90 (+2.00 along 180, add 1.00 to the 90)
>
> All three prescriptions specify exactly the same lens.

Thanks for your complete and succinct explanation. I have saved it for
the next time this question comes up.

--
Dan Abel
Petaluma, California USA
(E-Mail Removed)