Contribution%20of%20Ocular%20Response%20Analyzer%20for%20The%20study%20of%20Corneal%20Biomechanical%20Properties%20in%20Keratoconic%20Eyes

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Contribution of Ocular Response Analyzer for The
study of Corneal Biomechanical Propertiesin
Keratoconic Eyes

• Nicolas Fayol, MD (1,2),
• Olivia Abitbol, MD (1,2), Elodie Azan, MD (1,2),
• Thanh Hoang-Xuan , MD (1,2),
• Damien Gatinel, MD, PhD (1,2)
• Fondation Rothschild, Paris, France (1),
• Hôpital Bichat Claude-Bernard, Paris, France (2)

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Financial Disclosures

• The authors have no financial interest

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PURPOSE

• To compare corneal hysteresis (CH) and corneal
  resistance factor (CRF) measured with the
  Reichert Ocular Response Analyzer (ORA) in
  normal and keratoconic eyes.

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METHODS

• Retrospective observational study
• In this study, data were collected from 112
  normal and 112 keratoconic eyes.
• Keratoconus was diagnosed with clinical
  examination and corneal topography (Orbscan II,
  Bausch Lomb, Rochester, NY)
• Corneal hysteresis and corneal resistance factor
  were obtained with the Ocular Response Analyzer
  (ORA Reichert Ophthalmic Instruments, Buffalo,
  NY). The data were recorded by Generation 3
  software for ORA.
• We used a Student test to search for significant
  differences between the two groups (P lt 0.05).

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RESULTS

• The mean CH was 11.23 1.4 mm Hg (range,
  8.1-14.4) in normal eyes compared with 7.98 1.3
  mm Hg (range, 5.2-11.1) in keratoconic eyes. The
  difference was statistically significant (P lt
  0.0001, unpaired t-test).
• Mean CRF in the normal and keratoconic eyes was
  respectively 11.16 1.5 mm Hg (range, 7.7-14.6)
  and 6.8 1.4 mm Hg (3.5-10). The difference was
  statistically significant (P lt 0.0001, unpaired
  t-test).

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RESULTS

• We calculated the ratio CH/CRF. The mean CH/CRF
  was 1,0109 in normal eyes and 1,1958 in
  keratoconic eyes. The difference of this ratio
  between normal and keratoconic eyes was
  statistically significant
• (P lt 0.0001, unpaired t-test).

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• Table 1. Mean values of CH, CRF and ratio CH/CRF

Table 2. P values for CH, CRF and CH/CRF
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Figure 1. CH and CRF in keratoconic and normal
eyes
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Table 3. Demographic variables of patients
Table 4. Mean values of CCT and thinnest
pachymetry
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DISCUSSION

• Several studies showed a reduced corneal rigidity
  in keratoconic eyes. By taking two applanation
  pressures, ORA measured CH
  (viscoelasticity) which is the the difference
  between outward and inward pressures. Recently
  published papers agreed with our findings that CH
  in keratoconic eyes was lower than in normal eyes
• CRF is an indicator of overall resistance to the
  cornea, and is significantly correlated with
  central corneal thickness (CCT). In this study
  CRF was significantly lower in keratoconic eyes
  than in normal eyes.

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DISCUSSION

• The CH/CRF ratio was very close to 1 (1,0109) in
  normal eyes and was heigher (1,1958) in
  keratoconic eyes. The difference of CH/CRF
  between the two groups of eyes was statistically
  significant. This ratio could provide us a new
  indicator for the diagnosis of keratoconus.

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CONCLUSION

• In our series, both corneal hysteresis and
  corneal resistance factor was significantly lower
  in keratoconic eyes than in normal eyes. CRF
  decreases more than CH in keratoconic eyes with a
  ratio CH/CRF which was statistically different
  between keratoconic and normal eyes. This ratio
  could become an additional helpful data for the
  diagnosis of keratoconus.