Biomechanical Properties of Healthy and Keratoconic Corneas Evaluated Using an Ultra-High-Speed Scheimpflug Camera nznec Department of Ophthalmology University.

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Presentation transcript:

Biomechanical Properties of Healthy and Keratoconic Corneas Evaluated Using an Ultra-High-Speed Scheimpflug Camera nznec Department of Ophthalmology University of Auckland New Zealand Prof. Charles McGhee Assoc. Prof. Dipika Patel Hans Vellara Dr Noor Ali The authors have no financial interests to disclose

Biomechanics Elastic Viscous The cornea is viscoelastic Energy Dissipated

Keratoconus – pathological process manifests as an underlying biomechanical failure Biomechanics & Keratoconus Protrusion and thinningVogt’s StriaeTomographical changes

What is it? Air Tonometer Ultra high speed Scheimpflug camera How does it work? Air puff indents cornea Video 4333 frames/sec Calculates a range of output measurements Parameters describe in vivo biomechanics CorVis ST

CorVis ST - Parameters Applanation1 Time Length Velocity Highest Concavity Deformation Amplitude Radius of Curvature Peak Distance Applanation2 Time Length Velocity Parameters describe in vivo biomechanics

Response to an air-pulse is not purely corneal Deformation response to an air-pulse includes: corneal deformation and the globe being pushed into the socket Air pulse Globe pushed into orbit

Method 134 Normal vs. 75 KC eyes Prospective cross sectional study Total Cornea Orbit Derived separated components from CST videos Using principles described by Koprowski et al Compared purely corneal component (max value)

Method 134 Normal vs. 75 KC eyes Temp Sym. = 1 (Elastic)Temp Sym. >1 (Viscous) We also compared the symmetry of the response 1212

Method 134 Normal vs. 75 KC eyes We also investigated the energy dissipated (Area within the force vs. displacement graph) Typical force vs. corneal displacement graph from a normal patient.

CorVis ST – Normal vs. KC Results Normal KC P-value <0.001 Mean Age (years) Corneal thickness (µm) Max Corneal Deformation (mm) Temporal Symmetry Energy Dissipated

Results AUC = 0.77 (Max. Corneal Deformation) Normal Keratoconus Normal Keratoconus AUC = 0.60 (Temp. Symmetry) RoC Analysis – Not high enough to diagnose KC

Conclusion Temporal symmetry and maximum corneal deformation is significantly different between normal and KC eyes However, neither can be used alone to diagnose keratoconus