Comparison%20of%20VISX%20WaveScan%20aberrometer%20with%20NIDEK%20OPD-Scan.%20David%20Sungmin%20Kim,%20MD1,%20Julio%20Narvaez,%20MD2,%20Jabin%20Krassin,%20MD2,%20Khaled%20Bahjri,%20MD,%20MPH3.%201Loma%20Linda%20University%20Medical%20Center,%20Loma%20Linda,%20CA,%202Department%20of%20Ophthalmology,%20Loma%20Linda

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Comparison of VISX WaveScan aberrometer with
NIDEK OPD-Scan.David Sungmin Kim, MD1, Julio
Narvaez, MD2, Jabin Krassin, MD2, Khaled Bahjri,
MD, MPH3.1Loma Linda University Medical Center,
Loma Linda, CA, 2Department of Ophthalmology,
Loma Linda University Health Care, Loma Linda,
CA, 3Health Research Consulting Group, Loma Linda
University School of Public Health, Loma Linda,
CA.
The authors of this study do not have any
financial or proprietary interest in any product,
method, or material discussed.
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Zernike Pyramid
This figure was created by and used with
modifications with the permission of Patrick
Maeda.
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Wavefront Analyzers

• 2003, 67 were using wavefront analyzers in
  their practice. 1
• 2004, 89 were using wavefront analyzers in
  their practice 1
• In both years the VISX WaveScan was used 21 over
  all other wavefront analyzers combined. 1,2

• VISX WaveScan
• Wavefront Analyzer (Hartmann-Shack)
• Approximately 240 data points
• Autorefractor
• CustomVue platform (WaveScan, Star S4 excimer
  laser)

• NIDEK OPD-Scan ARK-10000
• Wavefront Analyzer (Automatic retinoscopy)
• 1440 data points
• Autorefractor
• Placido Disk Corneal Topographer
• Keratometer
• NAVEX platform (OPD-Scan, Final Fit software,
  EC-5000 excimer laser)
• Not yet FDA approved in the US

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WaveScan vs. OPD-Scan
Position-based aberrometry
Time-based aberrometry

• Different technologies

Same measurements?
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Purpose

• To compare measurements obtained with the VISX
  WaveScan and NIDEK OPD-Scan (ARK 10000).

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Subjects

• 92 eyes of 51 patients (measured with both
  aberrometers)
• Pupil size 6.0mm
• No ocular abnormality or surgery
• BCVA 20/30
• Average sphere -2.85 D (-6.75 to 5.00D)
• Average cylinder -0.73 D (-3.25 to 1.75)

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Methods

• Zernike coefficient values normalized to a 6.0mm
  pupil (Schwiegerling)3
• Normalized values used to calculate RMS values
• 2nd-6th radial orders
• 2nd-6th angular orders
• Total higher-order aberrations (3rd-6th radial
  order)
• 3rd-order trefoil (Z33 and Z33)
• 3rd-order coma (Z3-1 and Z31)
• Total spherical aberration (Z40 and Z60)
• Total coma (Z3-1, Z31, Z5-1, and Z51)
• Automated refractions versus manifest refractions
• Automated refractions versus automated refractions

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Results (Refractions)
Although no significant difference was found
between the NIDEK OPD-Scan and subjective
manifest refraction in the areas of sphere and
axis, the NIDEK OPD-Scan did measure
significantly higher cylinder. No significant
difference was found between the VISX WaveScan
and subjective manifest refraction.
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Results (HOAs)
The NIDEK OPD-Scan had significantly lower total
higher-order, second radial order, third order
coma, total spherical aberration, total coma, and
second angular order RMS values. The VISX
WaveScan had significantly lower cylinder,
trefoil, third-angular order, and fifth-angular
order RMS values.
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Results summary

• The two aberrometers are not interchangeable or
  equivalent
• The aberrometers had many significant
  differences, particularly in HOAs.
• The WaveScan with significantly higher values in
  more measurements.

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Discussion
The VISX WaveScan and the NIDEK OPD-Scan use two
different technologies. One could speculate that
the differences in the magnitude of the
aberration may be due to the differences between
the two technologies. One uses a Hartman-Shack
method while the other uses a dynamic skiascopy
method. The VISX uses from approximately 240 data
points for measurement while the NIDEK OPD-Scan
uses 1440 data points. The wavelength used for
measurement by the VISX WaveScan and the NIDEK
OPD-Scan are 780nm and 808nm, respectively. The
VISX WaveScan uses line of sight (the line
connecting the fixation point, pupil center, and
the fovea) as its measurement axis, while the
NIDEK OPD-Scan uses the visual axis (the line
connecting the fixation point, eyes nodal
points, and the fovea).4,5 Although both have
the capacity to offer the same measurements,
there are many possibilities to explain why they
might not. The results raise many important
questions including the following Are these
differences clinically significant? Which
machine represents better measurements? These
questions would be best answered with large
well-designed studies comparing objective and
subjective outcomes following customized
refractive surgeries using both aberrometers.
The development of a gold standard would also
make a great impact on refractive surgery - a
device such as that which the Optical Society of
America's taskforce is attempting to construct.4
Such a device would ideally allow all
aberrometers to be calibrated to a certain
standard. Overall, this study emphasizes the
importance and need for more studies comparing
wavefront aberrometers.
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References

• 1. Duffey RJ, Leaming D. US Trends in Refractive
  Surgery 2003 ISRS/AAO Survey. J Refract Surg.
  20052187-91.
• 2. Duffey RJ, Leaming D. US Trends in Refractive
  Surgery 2004 ISRS/AAO Survey. J Refract Surg.
  200521742-748.
• 3. Schwiegerling J. Scaling Zernike expansion
  coefficients to different pupil sizes. J Opt Soc
  Am A. 200219(10)1937-1945.
• 4. Thibos LN, Applegate RA, Schwiegerling JT,
  Webb R. Standards for reporting the optical
  aberrations of eyes. J Refract Surg
  200218S652-S661.
• 5. Rozema JJ, Van Dyck DEM, Tassignon MJ.
  Clinical comparison of 6 aberrometers. Part 1
  Technical Specifications. J Cataract Refract
  Surg 2005311114-1127.