[vslist] Query on unusual numbers coming out of Allegretto aberrometer

[Andrew Carkeet]

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 

Head of Visual Performance SERI

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