Spherical equivalent refraction?

Discussion in 'Optometry Archives' started by douglas, May 1, 2008.

  1. douglas

    douglas 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, May 1, 2008
    #1
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  2. douglas

    Salmon Egg Guest

    In article
    <>,
    douglas <> 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
     
    Salmon Egg, May 1, 2008
    #2
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  3. douglas

    douglas Guest

    On Apr 30, 10:37 pm, Salmon Egg <> wrote:
    > In article
    > <>,
    >
    >  douglas <> 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?
     
    douglas, May 1, 2008
    #3
  4. douglas

    Guest

    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 <> wrote:
    > On Apr 30, 10:37 pm, Salmon Egg <> wrote:
    >
    >
    >
    >
    >
    > > In article
    > > <>,

    >
    > >  douglas <> 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 -
     
    , May 1, 2008
    #4
  5. douglas

    Salmon Egg Guest

    In article
    <>,
    douglas <> wrote:

    > 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
     
    Salmon Egg, May 1, 2008
    #5
  6. douglas

    Jan Guest

    Salmon Egg schreef:
    > In article
    > <>,
    > douglas <> 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, May 1, 2008
    #6
  7. douglas

    Jan Guest

    Salmon Egg schreef:
    > In article
    > <>,
    > douglas <> 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 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
    > 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
     
    Jan, May 1, 2008
    #7
  8. douglas

    Zetsu 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...
     
    Zetsu, May 2, 2008
    #8
  9. douglas

    Dr Judy Guest

    On May 1, 12:34 am, douglas <> 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!
     
    Dr Judy, May 2, 2008
    #9
  10. douglas

    douglas Guest

    On May 1, 8:55 pm, Dr Judy <> wrote:
    > On May 1, 12:34 am, douglas <> 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?
     
    douglas, May 2, 2008
    #10
  11. douglas

    Dan Abel Guest

    In article
    <>,
    douglas <> wrote:

    > On May 1, 8:55 pm, Dr Judy <> wrote:
    > > On May 1, 12:34 am, douglas <> 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?


    It would be nice if you could take each of the world's professions and
    boil them down into one thing, but then they wouldn't be much of a
    profession, would they?

    I can see a few uses for SER, but it's definitely not a main focus.

    --
    Dan Abel
    Petaluma, California USA
     
    Dan Abel, May 2, 2008
    #11
  12. douglas

    Dr Judy Guest

    On May 2, 1:47 am, douglas <> wrote:
    > On May 1, 8:55 pm, Dr Judy <> wrote:
    >
    > >
    > > 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.

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


    For police officers, pilots, ship captains etc, the licensing agency
    sometimes has a concern about how well the person will see if glasses
    are lost or damaged during work. So they specify the maximum amount
    of refractive error.

    Judy
     
    Dr Judy, May 5, 2008
    #12
  13. douglas

    douglas Guest

    On May 5, 2:03 pm, Dr Judy <> wrote:
    > On May 2, 1:47 am, douglas <> wrote:
    >
    > > On May 1, 8:55 pm, Dr Judy <> wrote:

    >
    > > > 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.

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

    >
    > For police officers, pilots, ship captains etc, the licensing agency
    > sometimes has a concern about how well the person will see if glasses
    > are lost or damaged during work.  So they specify the maximum amount
    > of refractive error.
    >
    > Judy


    Oh yeah, I forgot.
     
    douglas, May 6, 2008
    #13
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