Ocular Response Analyzer Waveform Analysis in the Ectatic Corneas: Correlation of the New Corneal Biomechanics Parameters and Severity of Keratoconus

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Ocular Response Analyzer Waveform Analysis in the
Ectatic Corneas Correlation of the New Corneal
Biomechanics Parameters and Severity of
Keratoconus
Teeravee Hongyok, MD, Elisabeth J. Cohen, MD,
Kristin M. Hammersmith, MD, Peter R. Laibson, MD,
Christopher J. Rapuano, MD Cornea Service,
Wills Eye Institute Jefferson Medical College,
Thomas Jefferson University, Philadelphia,
Pennsylvania, USA The authors have no financial
interest in the subject matter for this
poster. World Cornea Congress VI, Boston, MA,
USA, April 7-9, 2010
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Introduction

• Ocular Response Analyzer (ORA) measurements of
  biomechanical properties of the cornea may be
  another helpful tool to help detect early
  keratoconus and aid in disease classification.
• Corneal hysteresis (CH) and corneal resistance
  factor (CRF) are significantly lower in
  keratoconic eyes compared to normal eyes, but the
  values overlap and can not distinguish between
  mild keratoconus and normal, when used alone.1, 2
  
• The ORA signal waveforms differ from normal
  waveforms in many ways, such as lower amplitude
  of applanation peaks in ectatic corneas compared
  to normals.3

1 Luce DA. J Cataract Refract Surg
200531(1)156-62. 2 Kirwan C, et. al.
Ophthalmologica 2008222(5)334-7. 3 Kerautret J,
J Cataract Refract Surg 200834(3)510-3.
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New ORA Waveform Parameters

• With new software (version 2.04), the ORA can
  mathematically describe waveform morphological
  characteristics including signal peak, width,
  slope, area under the curve, noise, and aspect
  ratio (height/width) of the waveform.
• We describe the new waveform parameters in
  figures below and tables in the following slide.

Fig.1
Fig.3
Fig.4
Fig.2
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Purpose

• To evaluate the correlation between the Ocular
  Response Analyzer (ORA) signal morphology using
  new waveform parameters and severity of disease
  in eyes with keratoconus and pellucid marginal
  degeneration.

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Methods

• Patients diagnosed with keratoconus and pellucid
  marginal degeneration on the Wills Eye Institute
  Cornea Service from March 2007 to April 2008 were
  prospectively enrolled in a study of patients
  with glaucoma or suspect glaucoma and age-matched
  controls.
• (Cohen EJ.,Trans Am Ophthalmol Soc. 2009
  Dec107282-99.)
• Eyes with previous ocular surgery or hydrops were
  excluded.
• Clinical and demographic characteristics were
  recorded. The corneal biomechanics were measured
  using the ORA with new software version 2.04.
• Corneal curvature and central thickness were
  measured using Humphrey Atlas 995 Topographer
  (Carl Zeiss Meditec, Inc., Dublin, Ireland) and
  AccuPach V (Accutome, Malvern, PA, USA).
• The correlation between ORA parameters and
  various disease severity indices were examined
  using Pearson correlation coefficients and a
  stepwise logistic regression model.

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Representative signals from keratoconic (KCN)
eyes without scarring
Moderate KCN
Mild KCN
Severe KCN

• The waveform morphology and biomechanical
  parameters were correlated with the severity of
  keratoconus.

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Correlation of Central Corneal Thickness and
Waveform Parameters
CCT

• There were significant correlations between
  central corneal thickness (CCT) and a number of
  ORA parameters including corneal hysteresis (CH),
  corneal resistance factor (CRF), Aindex, Bindex,
  W1, Aspect 1, Aspect11, Dslope 11, P1, and P2
  (plt0.05).
• Width of peak 1 (W1) was found to be the most
  significant predictor of CCT (r0.29, p0.006).

Plot of CCT and W1 (r0.29, p0.006)
W1
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Correlation of Waveform Parameters and Other
Characteristics

• Corneal scarring also significantly altered
  waveform morphology and various parameters
  including CH, CRF, Aindex, Bindex, Aspect1,
  Aspect2, Uslope1, Uslope2, H1, H2, Dive1, Dive2,
  Mslew2, Slew2, Uslope21, Uslope11, Dslope21, H11,
  H21, W1, P1 and WS (plt0.05).
• Location of maximal corneal ectasia did not
  significantly affect ORA parameters.
• These parameters were not significantly different
  between keratoconus and pellucid marginal
  degeneration.

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Conclusion

• We demonstrated that the corneal biomechanical
  parameters such as CH, CRF and also new ORA
  waveform parameter such as W1, and waveform score
  were significantly correlated to disease severity
  of ectatic corneas.
• These parameters might be helpful indicators to
  aid severity classification of keratoconus and
  pellucid marginal degeneration and monitor
  progression of the disease beyond the corneal
  thickness and corneal topography that have been
  used in the past.