Spherical equivalent refraction?

Main Page | Report this Page

Science Forum Index » Medicine - Vision Forum » Spherical equivalent refraction?

Page 1 of 1

Author

Message

douglas

Posted: Wed Apr 30, 2008 6:34 pm

Guest

What's "spherical equivalent refraction"? My --right eye--
prescription is -11.25 -2.50x178 --I believe this means that my lens
has a power of -11.25D at 178 degrees, and -13.75D at 88 degrees--,
and I heard of this term "spherical equivalent refraction", which
apparently is calculated by adding the spherical power, and
cylinderical power divided by 2, so this means I've got an SER of
-12.50D. What's the purpose of calculating the SER, how can it help my
ophthalmologist and optometrist?

Thanks!

douglas

Posted: Wed Apr 30, 2008 8:39 pm

Guest

On Apr 30, 10:37 pm, Salmon Egg <Salmon...@sbcglobal.net> wrote:

Quote:

In article
04f3541d-999a-4270-8cff-adff9820a...@n1g2000prb.googlegroups.com>,

douglas <Protoman2...@gmail.com> wrote:
What's "spherical equivalent refraction"? My --right eye--
prescription is -11.25 -2.50x178 --I believe this means that my lens
has a power of -11.25D at 178 degrees, and -13.75D at 88 degrees--,
and I heard of this term "spherical equivalent refraction", which
apparently is calculated by adding the spherical power, and
cylinderical power divided by 2, so this means I've got an SER of
-12.50D. What's the purpose of calculating the SER, how can it help my
ophthalmologist and optometrist?

Thanks!

This is one subject I get up on a soap box about.

The way prescriptions are given in terms of adding together spherical
power and cylindrical power. Unfortunately, this combination is not
unique and IIRC, optometrists and ophthalmologists have traditionally
not used the same convention to describe a prescription. If Zernike
functions were used instead, there would be a unique combination of one
spherical and two astigmatism functions. However, because cylindrical
lenses are easier to understand and manufacture, I do not expect Zernike
functions to take over soon.

Bill

Um, okayyyy...you didn't really answer my question. And what are
Zernike functions? How would my prescription be written using them?

Salmon Egg

Posted: Thu May 01, 2008 12:37 am

Guest

In article
<04f3541d-999a-4270-8cff-adff9820a384@n1g2000prb.googlegroups.com>,
douglas <Protoman2050@gmail.com> wrote:

Quote:

This is one subject I get up on a soap box about.

The way prescriptions are given in terms of adding together spherical
power and cylindrical power. Unfortunately, this combination is not
unique and IIRC, optometrists and ophthalmologists have traditionally
not used the same convention to describe a prescription. If Zernike
functions were used instead, there would be a unique combination of one
spherical and two astigmatism functions. However, because cylindrical
lenses are easier to understand and manufacture, I do not expect Zernike
functions to take over soon.

Bill

Guest

Posted: Thu May 01, 2008 5:14 am

Dear Doug,

Subject: Calculation of "Spherical Equivalent" power

You take your listed "Spherical" and add 1/2 the
astigmatic number. (Ignore the degrees.)

Thus, for example, your right eye:

-11.25 + ( -2.5 / 2 )

-11.25 + ( - 1.25 )

Spherical equivalent = 12.5 diopters, right eye.

Enjoy,

Or

What's "spherical equivalent refraction"? My --right eye--
prescription is -11.25 -2.50x178 --I believe this means that my lens
has a power of -11.25D at 178 degrees, and -13.75D at 88 degrees--,
and I heard of this term "spherical equivalent refraction", which

On May 1, 1:39 am, douglas <Protoman2...@gmail.com> wrote:

Quote:

On Apr 30, 10:37 pm, Salmon Egg <Salmon...@sbcglobal.net> wrote:

In article
04f3541d-999a-4270-8cff-adff9820a...@n1g2000prb.googlegroups.com>,

douglas <Protoman2...@gmail.com> wrote:
What's "spherical equivalent refraction"? My --right eye--
prescription is -11.25 -2.50x178 --I believe this means that my lens
has a power of -11.25D at 178 degrees, and -13.75D at 88 degrees--,
and I heard of this term "spherical equivalent refraction", which
apparently is calculated by adding the spherical power, and
cylinderical power divided by 2, so this means I've got an SER of
-12.50D. What's the purpose of calculating the SER, how can it help my
ophthalmologist and optometrist?

Thanks!

This is one subject I get up on a soap box about.

The way prescriptions are given in terms of adding together spherical
power and cylindrical power. Unfortunately, this combination is not
unique and IIRC, optometrists and ophthalmologists have traditionally
not used the same convention to describe a prescription. If Zernike
functions were used instead, there would be a unique combination of one
spherical and two astigmatism functions. However, because cylindrical
lenses are easier to understand and manufacture, I do not expect Zernike
functions to take over soon.

Bill

Um, okayyyy...you didn't really answer my question. And what are
Zernike functions? How would my prescription be written using them?- Hide quoted text -

- Show quoted text -

Salmon Egg

Posted: Thu May 01, 2008 2:16 pm

Guest

In article
<4821bc34-08e1-4c0e-85bf-dedd15d4ee70@r9g2000prd.googlegroups.com>,
douglas <Protoman2050@gmail.com> wrote:

Quote:

Um, okayyyy...you didn't really answer my question. And what are
Zernike functions? How would my prescription be written using them?

Zernike functions are one form of what are called orthogonal functions.
You have to know some mathematics beyond the typical mathematics
studied by nontechnical students. Zernike functions are being applied
in wavefront correction in refractive surgery.

Any smooth wavefront distortion introduced by the eye's structure can be
represented as a sum of such functions. This includes all kinds of
aberrations that cannot be corrected by spherical and cylindricl lenses.
There is one and only one way the individual Zernike functions can
describe the wavefront distortion of a given eye (except for measurement
error).

Bill

Jan

Posted: Thu May 01, 2008 5:16 pm

Guest

Salmon Egg schreef:

Quote:

In article
04f3541d-999a-4270-8cff-adff9820a384@n1g2000prb.googlegroups.com>,
douglas <Protoman2050@gmail.com> wrote:

What's "spherical equivalent refraction"? My --right eye--
prescription is -11.25 -2.50x178 --I believe this means that my lens
has a power of -11.25D at 178 degrees, and -13.75D at 88 degrees--,
and I heard of this term "spherical equivalent refraction", which
apparently is calculated by adding the spherical power, and
cylinderical power divided by 2, so this means I've got an SER of
-12.50D. What's the purpose of calculating the SER, how can it help my
ophthalmologist and optometrist?

Thanks!

This is one subject I get up on a soap box about.

The way prescriptions are given in terms of adding together spherical
power and cylindrical power. Unfortunately, this combination is not
unique and IIRC, optometrists and ophthalmologists have traditionally
not used the same convention to describe a prescription.

There are no problems in prescribing in minus or plus cylinder.
When prescribed with the plus cylinder the example above should be

S-13.75=C+2.50 axis 88

When prescribed with a minus cylinder it should be

S-11.25=C-2.50 axis 178

Both prescriptions are the same and every eyecare specialist in this
world can read and understand both.

The spherical equivalent is the same in both prescriptions

S-13.75 plus 1.25 (1/2 of the plus cylinder +2.50) results in 12.50
diopters.

S-11.25 plus -1.25 (1/2 of the minus cylinder -2.50) results also in
12.50 diopters.

Jan Oudesluys (normally Dutch spoken)

Jan

Posted: Thu May 01, 2008 5:34 pm

Guest

Salmon Egg schreef:

Quote:

There is a convention and there are no problems at all.

You may prescribe in minus or plus cylinders.

When prescribed with the plus cylinder the example above should be

S-13.75=C+2.50 axis 88

When prescribed with a minus cylinder it should be

S-11.25=C-2.50 axis 178

Both prescriptions are the same and every eyecare specialist in this
world can read and understand both.

The spherical equivalent is the same in both prescriptions

S-13.75 plus 1.25 (1/2 of the plus cylinder +2.50) results in -12.50
diopters.

S-11.25 plus -1.25 (1/2 of the minus cylinder -2.50) results also in
-12.50 diopters.

Jan Oudesluys (normally Dutch spoken)

If Zernike

Quote:

functions were used instead, there would be a unique combination of one
spherical and two astigmatism functions. However, because cylindrical
lenses are easier to understand and manufacture, I do not expect Zernike
functions to take over soon.

Bill

Zetsu

Posted: Thu May 01, 2008 5:45 pm

Guest

What's the use in all these complex formulas, I don't know. Just makes
things harder and longer for the laymen to work out what the pros are
chattering about. Can't we all just use a standardized refraction
measurement thingy? I mean, it would make things so much easier. Like,
just plain old 'minus 3' and 'axis 174' etc. Things us mere mortals
can actually identify with and have a clue what they imply...

Dr Judy

Posted: Thu May 01, 2008 5:55 pm

Guest

On May 1, 12:34 am, douglas <Protoman2...@gmail.com> wrote:

Quote:

SER doesn't have much purpose. For lower amounts of astigmatism it
can be used to determine soft lens power and spherical glasses power
for those who can't tolerate cylinder correction.

Some agencies that care about total refraction (police, pilot
licensing etc), may specify a maximum amount of refractive error that
will be allowed for their purposes. That amount is often specified as
SER.

Judy

Quote:

Thanks!

douglas

Posted: Thu May 01, 2008 7:47 pm

Guest

On May 1, 8:55 pm, Dr Judy <mpac...@rogers.com> wrote:

Quote:

On May 1, 12:34 am, douglas <Protoman2...@gmail.com> wrote:

What's "spherical equivalent refraction"? My --right eye--
prescription is -11.25 -2.50x178 --I believe this means that my lens
has a power of -11.25D at 178 degrees, and -13.75D at 88 degrees--,
and I heard of this term "spherical equivalent refraction", which
apparently is calculated by adding the spherical power, and
cylinderical power divided by 2, so this means I've got an SER of
-12.50D. What's the purpose of calculating the SER, how can it help my
ophthalmologist and optometrist?

SER doesn't have much purpose. For lower amounts of astigmatism it
can be used to determine soft lens power and spherical glasses power
for those who can't tolerate cylinder correction.

Some agencies that care about total refraction (police, pilot
licensing etc), may specify a maximum amount of refractive error that
will be allowed for their purposes. That amount is often specified as
SER.

Judy

Thanks!- Hide quoted text -

- Show quoted text -

Shouldn't they just care about your best corrected acuity?

Page 1 of 1 All times are GMT - 5 Hours The time now is Sat May 17, 2008 6:18 am Science Forum Index