Comparison of Central Corneal Thickness Measurements with Handheld Ultrasound Pachymetry and Three Other Imaging Technologies

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• Comparison of Central Corneal Thickness
  Measurements with Handheld Ultrasound Pachymetry
  and Three Other Imaging Technologies

J Ng1, S Velaedan1, W Wong2, L Thean1 1
Department of Ophthalmology, National University
Health Systems 2 Singapore Eye Research
Institute The authors have no financial interest
in the subject of matter in this poster.
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Introduction

• Measurement of central corneal thickness (CCT)
  plays an important role1 - 5
• Diagnostic assessment of corneal disorders
• Therapeutic assessment in glaucoma
• Significant parameter in refractive surgery
• Ultrasound pachymetry has been long regarded as
  the gold standard
• However, a number of new modalites have developed
  with recent times, including the Orbscan,
  Anterior Segment Optical Coherence Tomography
  (ASOCT), Ultrasound Biomicroscopy
• Handheld devices such as the PalmScan could
  provide a portable alternative for CCT
  measurements

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Purpose

• To compare the measurement of the central corneal
  thickness (CCT) by
• PalmScan, a handheld portable ultrasound
  pachymetry
• Sonomed ultrasound pachymetry
• Orbscan slit-imaging corneal topography and
• Visante anterior segment optical coherence
  tomography

PalmScan
Visante
Orbscan
Sonomed
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Design and Methodology

• Twenty-five normal subjects were recruited
• Observational, cross sectional study
• Each subject had CCT of both eyes measured by
  PalmScan, Sonomed, Visante and Orbscan
• All measurements were performed by either one of
  two observers
• Exclusion criteria
• Any previous intraocular surgery
• Contact lens wear within the last 1 week
• Active infection
• Any known corneal pathologies (e.g. keratoconus,
  dystrophies)
• Inability to cooperate
• Inability to provide informed consent

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Results
Age (years) 27.8 5.2
Gender (n25) Male Female 5 (20) 20 (80)
Race (n25) Chinese Malay Indian Others 16 (64) 5 (20) 3 (12) 1 (4)
CCT Machines N Mean (?m ) Std. Deviation (?m)
Sonomed 50 572.48 30.68
Orbscan 50 558.45 30.71
PalmScan 50 570.35 31.18
ASOCT 50 564.07 32.31
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Results

• Statistical evidence of difference in CCT
  readings obtained from 5 pair-wise comparisons of
  the Sonomed, PalmScan, Orbscan and ASOCT
  machines, except between Sonomed and PalmScan.

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Results

• Graphical exploration of Bland Altman plots shows
  similar results, where both Sonomed PalmScan
  has higher readings than Orbscan and ASOCT and
  there is no observed difference between Sonomed
  and Palmscan. Orbscan has the lowest readings.
  Table 1

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Results

• Table 1 Bland Altman plots

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Discussion

• Studies have been conducted extensively and
  concluded that ASOCT underestimated CCT compared
  to ultrasound pachymetry. This was demonstrated
  in our results as well.3
• Similarly, our study found that CCT measurements
  taken with ultrasound pachymetry, ASOCT and
  Orbscan are not directly interchangeable. This
  has been suggested to be a result of the
  different methodologies of the instruments.2,4
• The PalmScan, also a form of ultrasound
  pachymetry could potentially offer a more
  portable technology for measuring CCT. In our
  study, it is shown to be reliable and
  interchangeable with the Sonomed.

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Conclusion

• PalmScan is reliable alternative for CCT
  measurements.
• Although CCT measurements were well correlated
  amongst all 4 machines, the measurements should
  not be directly interchangeable in clinical
  practice except for possibly between the PalmScan
  and Sonomed.

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References

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  May115(5)796-801.e2. Epub 2007 Oct 4.
• Zhao PS, Wong TY, Wong WL, Saw SM, Aung T.
  Comparison of central corneal thickness
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  coherence tomography with ultrasound pachymetry.
  Am J Ophthalmol. 2007 Jun143(6)1047-9.
• Li EY, Mohamed S, Leung CK, Rao SK, Cheng AC,
  Cheung CY, Lam DS. Agreement among 3 methods to
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  Orbscan II, and Visante anterior segment optical
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  Oct114(10)1842-7. Epub 2007 May 15.
• Kim HY, Budenz DL, Lee PS, Feuer WJ, Barton K.
  Comparison of central corneal thickness using
  anterior segment optical coherence tomography vs
  ultrasound pachymetry. Am J Ophthalmol. 2008
  Feb145(2)228-232. Epub 2007 Dec 11.
• Leung DY, Lam DK, Yeung BY, Lam DS. Comparison
  between central corneal thickness measurements by
  ultrasound pachymetry and optical coherence
  tomography. Clin Experiment Ophthalmol. 2006
  Nov34(8)751-4.

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Thank You!