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Nicolas Fayol, MD (1,2), Olivia Abitbol, MD (1,2), Elodie Azan, MD (1,2),

Contribution of Ocular Response Analyzer for The study of Corneal Biomechanical Properties in 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)

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Nicolas Fayol, MD (1,2), Olivia Abitbol, MD (1,2), Elodie Azan, MD (1,2),

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  1. 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)

  2. Financial Disclosures The authors have no financial interest

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

  4. 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 < 0.05).

  5. 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 < 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 < 0.0001, unpaired t-test).

  6. 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 < 0.0001, unpaired t-test).

  7. Table 1. Mean values of CH, CRF and ratio CH/CRF Table 2. P values for CH, CRF and CH/CRF

  8. Figure 1. CH and CRF in keratoconic and normal eyes

  9. Table 3. Demographic variables of patients Table 4. Mean values of CCT and thinnest pachymetry

  10. 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.

  11. 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.

  12. 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.

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