How do I calculate SER? (Spherical Equivalent Refraction)

[nicola]

I'm not an optician and would like some advice.

I want to make a rough comparison of strength between some spectacles of
mine. In Wikipedia's entry for "Eyeglass Prescription" it says the formula
is:

Spherical Equivalent Refraction = sph + 0.5*cyl

Do I first need to convert the prescriptions of the specs into a different
notation? (I've read of something called plus-cylinder and minus-cylinder
notations).

One of my prescriptions is: +0.25 -3.00 5 -0.25 -3.25 173

(1) How do I do the S.E.R. calculation for that precription?

(2) How do I add 1.50 for reading before doing the calculation?

[Science_Research]

Hi - I am not an optician either.

That is a very "different" prescription. Check it again. Here is the
"math" of the conversion.

Roughly take 1/2 the "cyl" and add it to the initial sphere - as you
state.

+0.25 - 1.5 = -1.25 (Spherical Equivalent)

-0.25 - 1.62 (approx..) = -1.87, or -2.0 (approx.) spherical
equivalent.

I would ask the OD to re-do this measurement.

He could also make the measurement using ONLY a spherical minus lens -
for better accuracy.

Best idea - discuss these issues with him.

[Mike Tyner]

0"nicola" <nic...@mail.box.com> wrote

> I want to make a rough comparison of strength between some spectacles of
> mine. In Wikipedia's entry for "Eyeglass Prescription" it says the formula
> is:
>
> Spherical Equivalent Refraction = sph + 0.5*cyl
>
> Do I first need to convert the prescriptions of the specs into a different
> notation? (I've read of something called plus-cylinder and minus-cylinder
> notations).

No plus-minus conversion is needed if you carefully respect the signs of
each term.

> One of my prescriptions is: +0.25 -3.00 5 -0.25 -3.25 173

That's two prescriptions, probably right (OD) and left (OS).

Using the SE formula on the first one:
half of -3.00 is -1.50
Add -1.50 to +0.25
SE is -1.25.

On the second one:
half of -3.25 is -1.62
Add -1.62 to -0.25
SE is -1.87

> (2) How do I add 1.50 for reading before doing the calculation?

You wouldn't; you'd do SE first, but the add is an independent variable that
only confounds the original question of how much your distance vision has
changed.

-MT, OD

[Mike Tyner]

"Science_Research" <otis...@embarqmail.com> wrote

> I would ask the OD to re-do this measurement.

Yes, but you're the village idiot.

> He could also make the measurement using ONLY a spherical
> minus lens - for better accuracy.

If you had any experience or training, you would know this DECREASES

accuracy.

> Best idea - discuss these issues with him.

Best idea - don't tell an engineering newsgroup to use flat head
screwdrivers on Phillips head screws.

[Science_Research]

Subject: The error-prone "astigmatic" measurement.

http://www.youtube.com/watch?v=IhbqhW08sH0

I always insisted that I require spherical lenses.

In fact, that is the second-opinion on most "cylinder" measurements.

Enjoy,

[Mike Tyner]

"Science_Research" <otis...@embarqmail.com> wrote

> I always insisted that I require spherical lenses.

Yes, but you have no training or experience with 3 diopters of cylinder.

Look through a trial lens with 3 diopters of cyl and you'll see why you're
an idiot.

> In fact, that is the second-opinion on most "cylinder" measurements.

As I said, you have no training or experience.

-MT

[Szczepan Bialek]

"Mike Tyner" <mty...@mindspring.com> napisa� w wiadomo�ci
news:dqudncA4Tco7-v3M...@giganews.com...

Somebody wrote: " Your correct, some people can not tolerate the Cyl. - and
would prefer not to wear it."

What is better: Do not wear the minus 3 diopters of cyl or wear the
spherical minus 1.5?
S*

[Science_Research]

Subject: The choice to wear a "Spherical" lens - if you pass the
20/20 line?

A mild amount of "astigmatism", (i.e.., -1 diopters or less), you can
request that only a "spherical" lens be provided.

Since I have self-confirmed 20/20, I do not choose to wear any lens
for distance. But I always suggest the person check this himself.

I got headaches from wearing an "astigmatic" lens all the time. That
is why I insisted on being given this choice.

Enjoy,





On Apr 7, 4:16 am, "Szczepan Bialek" <sz.bia...@wp.pl> wrote:
>  "Mike Tyner" <mty...@mindspring.com> napisa w wiadomo cinews:dqudncA4Tco7-v3M...@giganews.com...
>
>
>
> > "Science_Research" <otisbr...@embarqmail.com> wrote

[Szczepan Bialek]

"nicola" <nic...@mail.box.com> napisa� w wiadomo�ci
news:XnsA198A9D3...@178.22.82.21...

> I'm not an optician and would like some advice.
>
> I want to make a rough comparison of strength between some spectacles of
> mine. In Wikipedia's entry for "Eyeglass Prescription" it says the formula
> is:
>
> Spherical Equivalent Refraction = sph + 0.5*cyl
>
> Do I first need to convert the prescriptions of the specs into a different
> notation? (I've read of something called plus-cylinder and minus-cylinder
> notations).
>
> One of my prescriptions is: +0.25 -3.00 5 -0.25 -3.25 173

I am not an expert. But I know that the eyes with the sphere -3 are excelent
for reading.
You have the -3 cyl. Are you able to read without galsses?
S*

[nicola]

On 17:17 7 Apr 2013, Szczepan Bialek wrote:

>
> "nicola" <nic...@mail.box.com> napisał w wiadomości

No, I can not read without glasses. I have a lot of astigmatism. Maybe that
is why?

[nicola]

Thank you for your help. You are correct that one of the prescriptions I
gave was for the left and the other for the right.

In my case the "add" is important because I want to compare the reading
parts of two bifocal prescriptions. I'll try to explain my situation
below.

The two bifocals specs are each made with the upper part for a computer
screen and the lower part for reading papers close to me on the desk.
One was made up about 12 months before the other so they have slightly
different prescriptions.

Both are reasonably clear but seem to focus best at different distances
which is why I want a rough value (like the S.E.R.) to compare lens
strengths. Of course I have to compare upper and lower parts
separately.

I would like to know how I include the "add" value in the S.E.R. Can I
simply add the reading "add" value to the S.E.R.? (I think the "add" is
the sph value, isn't it?) The actual prescriptions are as follows:

FIRST BIFOCALS
R) +0.50 -3.00 4 L) pl -3.25 175
add 1.00
add 1.75

SECOND BIFOCALS
R) +0.25 -3.00 5 L) -0.25 -3.25 173
add 1.25
add 1.75

[Mike Tyner]

For your purpose, the add is "added" to the sphere portion only. It makes no
sense to add it to the cylinder also.

I don't really understand how you are applying two different bifocal powers.

I design these several times a day but my method and notation may be
different from yours.

-MT



"nicola" <nic...@mail.box.com> wrote

[endyr...@gmail.com]

In practice we prescribe spherical equivalent when the cylinder power is small. From the prescription you gave us, you have a cylinder power of about -3.00. That's quite much for anybody to prescribe a sphere. I will advice you stick to a spherocyl prescription. Hope this helps you.