[vslist] Query on unusual numbers coming out of Allegretto aberrometer
Andrew Carkeet
seri_acarkeet@snec.com.sg
Fri May 31 11:11:06 2002
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I'm working at the Singapore Eye Research Institute and last weekend I =
had a look at the Allegretto aberrometer at a conference here in =
Singapore. We do aberrations research and are possibly interested in =
obtaining instruments like this for our lab.
The instrument displays an output for RMS which looks wrong. (I also had =
a query about the Zernike coefficients generated, but then I realized =
they were from unweighted equations and I normally use Optical Society =
of America coefficients, so converting should be easy). But the display =
for RMS is harder for me to understand, it looked too small to me. I =
took as an example, some data for a 6mm pupil diameter. The refraction =
was -5.35/-0.41 x 95 and the machine gave a second order RMS of 3.17421 =
(I think the units were microns, maybe this is where I'm wrong). I did =
a quick calculation of the RMS for the equivalent sphere (-5.52) over a =
6 mm pupil and came up with 7.21 microns (based on Z 2,0). Then I =
thought maybe the equation I'd worked out for RMS was wrong and I =
roughly checked by discretely calcuating the RMS for samples at 0.5 mm =
intervals across the pupil and got 7.3 microns (close enough for my =
rough method).
Does anyone have any knowledge of this instrument that might solve this =
dilema?
Andrew Carkeet=20
Head of Visual Performance SERI
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<DIV><FONT face=3DArial size=3D2>
<DIV><FONT face=3DArial size=3D2>I'm working at the Singapore Eye =
Research Institute=20
and last weekend I had a look at the Allegretto aberrometer at a =
conference here=20
in Singapore. {We do a"errations research and are possibly =
interested in=20
obtaining instruments like this for our lab.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>The instrument displays an output for =
RMS which=20
looks wrong. (I also had a query about the Zernike coefficients =
generated, but=20
then I realized they were from unweighted equations and I normally use =
Optical=20
Society of America coefficients, so converting should be easy). But the =
display=20
for RMS is harder for me to understand, it looked too small to me. I =
took as an=20
example, some data for a 6mm pupil diameter. The refraction was =
-5.35/-0.41 x 95=20
and the machine gave a second order RMS of 3.17421 (I think the =
units were=20
microns, maybe this is where I'm wrong). I did a quick calculation =
of the=20
RMS for the equivalent sphere (-5.52) over a 6 mm pupil and came up with =
7.21=20
microns (based on Z 2,0). Then I thought maybe the equation I'd =
worked out=20
for RMS was wrong and I roughly checked by discretely calcuating the RMS =
for samples at 0.5 mm intervals across the pupil and got 7.3 =
microns (close=20
enough for my rough method).</FONT></DIV>
<DIV> </DIV>
<DIV>Does anyone have any knowledge of this instrument that might solve =
this=20
dilema?</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>Andrew Carkeet </FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>Head of Visual Performance =
SERI</FONT></DIV>
<DIV> </DIV></FONT></DIV></BODY></HTML>
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