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Medical Forum / General / Vision / May 2008Spherical equivalent refraction?
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! In article <04f3541d-999a-4270-8cff-adff9820a384@n1g2000prb.googlegroups.com>, > What's "spherical equivalent refraction"? My --right eye-- > prescription is -11.25 -2.50x178 --I believe this means that my lens [quoted text clipped - 6 lines] > > 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 > In article > <04f3541d-999a-4270-8cff-adff9820a...@n1g2000prb.googlegroups.com>, [quoted text clipped - 22 lines] > > Bill Um, okayyyy...you didn't really answer my question. And what are Zernike functions? How would my prescription be written using them? 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 > > In article > > <04f3541d-999a-4270-8cff-adff9820a...@n1g2000prb.googlegroups.com>, [quoted text clipped - 27 lines] > > - Show quoted text - In article <4821bc34-08e1-4c0e-85bf-dedd15d4ee70@r9g2000prd.googlegroups.com>, > 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 schreef: > In article > <04f3541d-999a-4270-8cff-adff9820a384@n1g2000prb.googlegroups.com>, [quoted text clipped - 16 lines] > 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) Salmon Egg schreef: > In article > <04f3541d-999a-4270-8cff-adff9820a384@n1g2000prb.googlegroups.com>, [quoted text clipped - 16 lines] > 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 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... > What's "spherical equivalent refraction"? My --right eye-- > prescription is -11.25 -2.50x178 --I believe this means that my lens [quoted text clipped - 4 lines] > -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! > > What's "spherical equivalent refraction"? My --right eye-- > > prescription is -11.25 -2.50x178 --I believe this means that my lens [quoted text clipped - 19 lines] > > - Show quoted text - Shouldn't they just care about your best corrected acuity? In article <9b6e2170-1e92-40b8-9379-6f07acb42bd5@l17g2000pri.googlegroups.com>, > > > What's "spherical equivalent refraction"? My --right eye-- > > > prescription is -11.25 -2.50x178 --I believe this means that my lens [quoted text clipped - 21 lines] > > 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.  SignatureDan Abel Petaluma, California USA dabel@sonic.net > > SER doesn't have much purpose. For lower amounts of astigmatism it > > can be used to determine soft lens power and spherical glasses power [quoted text clipped - 6 lines] > > 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 > > > SER doesn't have much purpose. For lower amounts of astigmatism it > > > can be used to determine soft lens power and spherical glasses power [quoted text clipped - 13 lines] > > Judy Oh yeah, I forgot. |
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