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Analysis of Corneal Biomechanical Properties in Keratoconus Using Ocular Response Analyzer

Analysis of Corneal Biomechanical Properties in Keratoconus Using Ocular Response Analyzer. Hyuck Jin Choi, Joo Youn Oh, Won Ryang Wee, Mee Kum Kim, Ji Won Kwon, Sang Mok Lee, MD, Jin Seok Choi, MD. Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea

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Analysis of Corneal Biomechanical Properties in Keratoconus Using Ocular Response Analyzer

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  1. Analysis of Corneal Biomechanical Properties in Keratoconus Using Ocular Response Analyzer Hyuck Jin Choi, Joo Youn Oh, Won Ryang Wee, Mee Kum Kim, Ji Won Kwon, Sang Mok Lee, MD, Jin Seok Choi, MD Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea Seoul Artificial Eye Center, Seoul National Univerisity Hospital Clinical Research Institute, Seoul, Korea

  2. Financial Disclosure • The authors of this poster have no financial interest in the subject matters.

  3. Introduction • Biomechanical Properties of Cornea • Hysteresis • A property of physical systems that do not instantly follow the forces applied to them, but react slowly, or do not return completely to theior original state • Etymology: ‘ late, fall short’ in ancient Greek • Corneal Hysteresis (CH) • The the difference betweenthe inward (P1) and outward (P2) pressure valuesobtained during the dynamic bi-directional applanation process employed in the Ocular Response Analyzer, as a result of viscous damping in the cornea. • P1 – P2 • Corneal Resistance Factor (CRF) • the overall resistance of the cornea, including both the viscous and elastic properties (total visco-elasticity) • P1 – 0.7 x P2

  4. Ocular Response Analyzer

  5. Introduction • Biomechanical Properties of Cornea • Corneal-compensated intraocular pressure (IOPcc) • Less affected by corneal properties than other tonometry • P2 – 0.43 x P1 • Goldmann-correlated intraocular pressure(IOPg) • the overall resistance of the cornea, including both the viscous and elastic properties (total visco-elasticity) • P1 – 0.7 x P2 • Previous Studies • Normal Value of CH, CRF • CH = 10.8 ±1.5 mmHg, CRF = 11.0 ±1.6 mmHg (n=165) • (Ortiz et al. IOVS 2007) • CH = 10.9 ±1.6 mmHg, CRF = 11.0 ±1.6 (n=70) • (Kirwan et al. Ophthalmologica 2008) • Keratoconus, Post-LASIK • CH and CRF ⇒low • (Shah et al. IOVS 2007, Pepose et al. AJO 2007, • Susan et al. BJO 2008, Kerautret et al. JCRS 2008)

  6. Purpose • To assess the correlation between corneal biomechanical properties such as corneal hysteresis(CH) or corneal resistance factor(CRF) measured by the Ocular Response Analyzer(ORA) and topographic parametersmeasured with ORB scan

  7. Methods • Subjects • Period of data collection • June 1, 2008 – September 31, 2008 • Outpatient clinic, Seoul National University Hospital • Inclusion criteria • Subjects who met keratoconus index • Control group • Age and sex-matched normal eyes Modified Rabinowits Keratoconus Index • Parameters • Ocular Response Analyzer • Corneal hysteresis(CH), corneal resistance factor(CRF), corneal-compensated IOP(IOPcc), Goldmann-correlated IOP(IOPg) • ORB scan • Central curvature, I-S 3mm, I-S 6mm, SimK Max, SimK min, Simk astig, 3mm irregular astig, 5mm irregular astig, CCT

  8. Results 1. Subject Characteristics Fisher’s exact test; Mann-Whitney U test 2. ORA between KC and Control CH, CRF IOP

  9. Results 3. . Correlation Analysis in KC CH – CRF CH / CRF 2. ORA between KC and Control CH, CRF Spearman’s correlation coefficient

  10. Results 3. . Correlation Analysis in KC IOPcc-IOPg IOPcc/IOPg Spearman’s correlation coefficient

  11. Discussion • Corneal biomechanical changes in keratoconus • B oth CH and CRF in keratoconus ⇒ lo w er than normal control • CRF decreased more than CH. • As corneal thicknessdecreases, biomechanical stability decreases • Combined parameters in keratoconus • IOPcc-g and IOPcc/g • IOPcc = IOPg + Corneal factor • ⇒Corneal factor = IOPcc - IOPg • If IOPcc-gorIOPcc/gis high, there is corneal biomechanical change morethan normal condition. • GAT can be underestimated in keratoconus. • Correlation Analysis with ORB Scan • CH-CRF, CH/CRF • CCT w as negatively correlated • As w ell as CCT, simK value and irregular astigmatism of 3mm and 5mm were also positively correlated. • IOPcc-g, IOPcc/g • Only CCT w as negatively correlated

  12. Discussion • About keratoconus suspect • Possibility to detect early keratoconus change or progression. • Limitations • Cross-sectional study • Difficult to generalize into the changein subject • Suggestions for future studies • Study to find the risk factors of post-LASIK ectasia with various ORA parameters. Conclusions • The corneal biomechanical parameters and their combined parameters measured using Ocular Response Analyzer were correlated with topographic parameters. • So there is a possibility to put the biomechanical parameters to practical use in detecting and monitor keratoconus.

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