Comparison of Automated and Manual Measurements of Horizontal Corneal Diameter in Contact Lens Weare

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Comparison of Automated and Manual Measurements
of Horizontal Corneal Diameter in Contact
LensWearers Using Orbscan Eye Metrics Function
and Orbscan 11z Corneal Topographer

• Dr Venkataraman Arvind MD , MRCOphth.
• M.Krithiga B.S.(Optom)
• Vasan Eye Care Hospital,
• Chennai, India

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Financial disclosure

• The authors have no financial interest in this
  study or presentation

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AIM

• Comparison of automated and manual measurements
  of horizontal corneal diameter in contact lens
  wearers using Orbscan Eye Metrics Function and
  Orbscan 11z corneal topographer.

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METHODS

• Automated White to White (WTW) measurement was
  obtained from the Orbscan II.
• Using the Eye metrics function the WTW was
  measured manually by two observers along the five
  point corneal reflections on the Orbscan real
  image.
• The data was analysed using Statistica software
  for correlation ,reliability and Inter-rater
  repeatability.

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Orbscan WTW
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WTW WITH EYEMETRICS
5 point corneal reflections through which WTW is
measured
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Results

• 73 eyes of 37 patients were included in the
  study.
• 25 females and 12 males.
• Average duration of contact lens usage was 34
  months (range 16-52 months).
• All of them were using soft contact lenses

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Results
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Results
Obs A
Obs B
Orbscan
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RESULTS

• Manual measurements (Observer AB) using eye
  metrics was statistically different compared to
  the automated measurements of Orbscan (plt0.001).
• Standard deviation difference
• Orbscan Vs OB-A is 0.19
• Orbscan Vs OB-B is 0.10

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Results
Correlation R 0.0009(pgt0.05). Slope -0.008
(Pgt0.05). Intercept -0.079 (P 0.05).
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Results
Observer A Observer B
Average of measurements of Observer A B
Correlation R 0.0043(pgt0.05). Slope -0.0336
(Pgt0.05). Intercept 0.468 (P 0.05).
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Results

• Horizontal corneal diameter by manual Eye metrics
  measurements are longer than Orbscan derived
  measurements.
• Manual measurement shows higher
• inter-rater variability and test retest
  variability.
• Variations tend to decrease with repeat
  measurements.

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Conclusion

• Orbscan IIz corneal topographer underestimates
  the WTW especially in long term contact lens
  wearers. This error can be reduced by manual
  measurements using Eye metrics software.
• Manual corneal measurement can be very useful in
  patients with pannus and other peripheral corneal
  changes.
• This method will be very useful adjuvant to
  automated measurement of corneal diameter in
  selection of Phakic intraocular lenses ( ICLs)
  and ACIOLs.

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Thank you