Comparison of Corneal Thickness Measurement by Ultrasound Pachymetry, Konan Noncontact Optical Pachy

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Comparison of Corneal Thickness Measurement by
Ultrasound Pachymetry, Konan Non-contact Optical
Pachymetry and Orbscan II Analyzer System

• Christensen¹ J. Narvaez¹
• 1. Ophthalmology, Loma Linda University, Loma
  Linda,CA,USA

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Principal Investigator

• Julio Narvaez, M.D.
• Associate Professor
• Cornea, Anterior Segment, Refractive Surgery
• Loma Linda University Department of Ophthalmology
• Loma Linda, California

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Purpose

• To assess the repeatability and validity of two
  optical techniques for determination of central
  corneal thickness, in comparison with the
  standard ultrasound pachymetry.

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Method

• We measured 100 eyes of 50 normal volunteers,
  ages 22 to 74 with three consecutive techniques.
  Subjects with previous surgery, or keratoconus
  were excluded.

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Method

• Corneal thickness was measured with Konan
  Non-Contact optical pachymetry, Orbscan II
  Analyzer, and conventional ultrasonic
  pachymetry. Each eye was measured twice with each
  of the optical techniques in alternation,
  anesthetic drops were then instilled and three
  ultrasound measurements were then obtained.

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Methods

• The instruments were compared to each other with
  regard to repeatability. Validity was analyzed by
  comparison to the ultrasound measurements. The
  intraclass correlation coefficients were
  calculated and their confidence intervals were
  determined.

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Results

• Measurements (in micrometers) of corneal
  thickness with Konan, Orbscan and ultrasound.
  Ultrasound is the mean of three measurements.

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Results
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Results

• For reliability the Ultrasound measurements was
  found to have an ICC of 0.905 (95 CI 0.870 to
  0.932).
• The Konan measurements had an ICC of 0.947 (95
  CI 0.922 to 0.964).
• The Orbscan measurements yielded an ICC of 0.972
  (95 CI 0.959 to 0.981).

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Scatterplots for Reliability Analysis of Konan
and Orbscan
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Results

• Validity was established by a comparison of
  each of the optical measurements to the mean of
  three ultrasound measurements.
• The validity of the first Konan measurement
  had an ICC of 0.730 (95 CI 0.623 to 0.810) and
  the second measurement was similar at 0.736 (95
  CI 0.631 to 0.814).
• The first Orbscan measurement had an ICC of
  0.865 (95CI 0.805 to 0.907) and the second
  measurement produced an ICC of 0.872 (95 CI
  0.816 to 0.912).

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Scatterplots Comparing Validity of Konan and
Orbscan
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Conclusions

• Both of the newer optical methods for determining
  corneal thickness produced results that were more
  repeatable than the standard ultrasound
  technique.
• The Orbscan analyzer was more repeatable and had
  higher validity than the Konan optical
  pachymeter.