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Renato Ambrósio Jr., MD, PhD* Diogo L. Caldas, MD Isaac C. Ramos, MD Rodrigo T. Santos, MD

Corneal Biomechanical Assessment using Dynamic Ultra High-Speed Scheimpflug Technology Non-Contact Tonometry (UHS-ST NCT): Preliminary Results. Renato Ambrósio Jr., MD, PhD* Diogo L. Caldas, MD Isaac C. Ramos, MD Rodrigo T. Santos, MD Leonardo N. Pimentel, MD Cynthia Roberts, PhD*

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Renato Ambrósio Jr., MD, PhD* Diogo L. Caldas, MD Isaac C. Ramos, MD Rodrigo T. Santos, MD

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  1. Corneal Biomechanical Assessment using Dynamic Ultra High-Speed Scheimpflug Technology Non-Contact Tonometry (UHS-ST NCT): Preliminary Results Renato Ambrósio Jr., MD, PhD* Diogo L. Caldas, MD Isaac C. Ramos, MD Rodrigo T. Santos, MD Leonardo N. Pimentel, MD Cynthia Roberts, PhD* Michael W. Belin, MD* Dr. Ambrósio & Dr. Belin are consultants for Oculus Optikgeräte GmbH (Wetzlar, Germany) and have received research funding and travel reimbursements

  2. Introduction: Evolution on Corneal Propedeutics • “Propedeutics” refers (in Medicine) to the collection of data about a patient by observations and examinations. • Advances are recognized on the ability for architecture or goemetrical characterization of the cornea • Keratometry, Keratoscopy, Videokeratography, Corneal Topography, Corneal Tomography

  3. Corneal Biomechanics: Relevance • From Geometrical and Optical understanding, the next step is biological evaluation: healing response and biomechanics • Ectasia mysteries* in Refractive Surgery had highlight the need for corneal biomechanical understanding • (*ie: cases with no risk factors that develop ectasia after LASIK) • Also to Customize Refractive Corneal Treatments; correctly measure IOP (intraocular pressure) and to possibly predict glaucoma risk • Corneal biomechanical evaluations were limited to in vitro studies and to mathematical finite element models until the Ocular Response Analyzer (ORA-Reichert, Depew) in 2005 • New techniques are under development for evaluating biomechanics • This e-Poster presents a new system – The Corvis ST (Oculus, Wetzlar, Germany) with preliminary clinical results.

  4. The Oculus Corvis ST • Ultra High-Speed (UHS ST) Scheimpflug Technology takes 4,330 frames/sec with 8mm horizontal coverage • Monitors corneal deformation response to a symmetrically metered air pulse 1. Natural; (Ingoing Phase) 2. First Applanation (1st A) Momentum; 3 and 4. Ingoing Concavity Phase; 5. Highest Concavity Momentum; 6. Oscillation Period; (Outgoing Phase); 7. Second Applanation (2nd A) Momentum; 8. After Second Applanation; 9. Natural Back 1st Applanation, Highest Concavity and 2nd Applanation: Time and Length; Maximum Deformation; Maximum Velocity In and Out; Thickness

  5. Corvis ST: First Studies • Experiment involving contact lenses mounted on an artifical pressurized chamber (Caldas et al., ePostar ASCRS 2011) found that the deformation response is influenced by lens properties and chamber pressure. • The inspection of the actual deformation process details corneal characterization, which has a potential for distinguishing normal (A, B) and keratoconus (C, D) corneas (see video* PosterASCRS2011_clip_RAmbrosio). Natural and Highest Deformation Momentum in a Normal (A, B) and a Keratoconic (C, D) Cornea

  6. Corvis ST: Clinical Parameters • IOP: is the NCT measurement based on the 1st Applanation • 1st A-time: is the time from starting • until the first applanation • HC-time: time from starting until • Highest Concavity is reached • 2nd A-time: time from starting • until the second applanation • 1st A length: cord length of the first applanation • 2nd A length: cord length of the second applanation • Def Amp: maximum amplitude at the apex (highest concavity) • W-Dist: distance of the two “knee’s” at highest concavity (HC) • Curvature Rad HC: central concave curvature at HC • Curvature Rad normal: initial central convex curvature • Vin: corneal speed during the first applanation moment • Vout: corneal speed during the second applanation moment

  7. Clinical Study • The Corvis ST was utilized to assess corneal deformation response in one eye from 71 keratoconic patients and in one eye from 178 normal patients. • Clinical diagnosis was based on the complete eye exam, Placido-disk based corneal topography and Pentacam Corneal Tomography. • Statistically significant distributions for all parameters (Mann-Whitney, p<0.05), but with significant overlap and AUC • (area under the ROC curves) between 0.673 and 0.852

  8. Corvis Combo1: combined parameter • Joint work with “Instituto de Computação” at UFAL (Universidade Federal de Alagoas*) to develop a combined parameter (Corvis Combo1) based on a linear regression analysis, considering the effects of IOP on deformation response parameters • 0.033 * IOP - 0.004 * Pachy Apex - 0.448 * 1st A Time - 0.049 * HC Time + 0.093 * 2nd A Time + 0.026 * 1st A Length(max) - 0.105 * 2nd A Length(max) + 0.208 * Def Amp (max) - 0.619 * W-Dist - 0.021 * Curv, Rad, HC - 0.101 * Curv, Rad, Normal - 0.525 * Vin - 0.166 * Vout + 7.952 * Prof. Aydano P. Machado & J. M. Lyra, MD, PhD

  9. Clinical Study • The Corvis ST Combo1 performed statistically better (p<0.05; Pairwise ROC comparisons) than the individual parameters from the Corvis ST to distinguish 71 keratoconic eyes and 178 normal eyes (one eye per patient included) • This approach has been complementary to enhance the diagnosis of ectasia susceptibility.

  10. Clinical Correlations • There were very significant correlations (Spearman, p<0.001) between IOP and 1st Applanation Time (rho=0.94), 2nd Applanation Time (rho=-0.73), Deformation Amplitude (rho=-0.80), W-Dist (rho=-0.66), Curv Rad HC (rho=0.45), Vin (rho=-0.49), Vout (0.38) and Combo1 (rho=-0.44) • There was a significant correlation (Spearman, p<0.01) between Pachymetry at the Apex and IOP (rho=0.37), 1st Applanation Time (rho=0.4 ) and Lengh (rho=-0.18 ), W-Dist (rho=-0.25), Curv Rad HC (rho=0.48), Vout (rho=0.3), and Combo1 (rho=-0.64) • There was a weak correlation between age and HC Time (Spearman, p=0.0039; rho=0.22)

  11. Enhanced Screening for Ectasia Susceptibility • Biomechanical data from Corvis ST enhances the capability to detect very mild cases of ectasia and also help to characterize stable cases with asymmetric bow tie and inferior steepening (ABT/IS). • 26 eyes diagnosed as FormeFruste Keratoconus (FFKC), with normal front curvature map while the fellow eye has keratoconus were examined. • 25 eyes with ABT/IS but with no other clinical or tomographic sign of ectasia were examined. • Combo1 • 21/26 (80%) eyes with FFKC >0.21 • 24/178 (13%) normal eyes <0.21 • 8/25 (32%) ABT/IS cases <0.21 Kruskall-Wallis Test see video* PosterASCRS2011_clip_RAmbrosio

  12. Corvis ST: Conclusions • The inspection of corneal deformation during NCT enables biomechanical characterization • The deformation is severely influenced by IOP • Combo1 from Corvis ST provides clinically relevant parameter to enhance sensitivity and specificity to detect ectasia. ABT with no Ectasia (A,B) x FFKC (C, D) • This approach is complementary to Corneal Tomography with the Pentacam for screening refractive candidates Combo 1=0.16 Combo 1=0.31

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