What does Korvis measure?

A) Motion parameters and deformation
• A1/A2 velocity
• Deformation amplitude
• Peak distance
• Radius of curvature during deformation

b) IOP and Tonometry parameters
• bIOP (biomechanically corrected IOP)

c) Combined biomechanical parameters
• CBI (Corvis Biomechanical Index)
• TBI (Tomographic-Biomechanical Index; combination of Corvis + Pentacam)

d) estimated stiffness modulus
• Stress–Strain Index (SSI)
which is an alternative to Young's modulus in stroma.

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2) Are these the real biomechanics of the cornea?

Corneal biomechanics in the full sense includes:
• Young's modulus
• Hysteresis
• Viscoelastic behavior
• Real stress-strain models
• Collagen lamellar architecture
• Non-IOP-dependent behavior
• Nonlinear tissue response (nonlinear elasticity)

Corvis does not measure any of these directly.
Instead:
• Creates an external stimulus (air puff)
• Films the dynamic response of the cornea
• From this response, tissue behavior is inferred

So it is not the most accurate biomechanical measurement, but a proxy with high reliability.

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3) How close is Corvis to real biomechanics?

Studies show:
• SSI has a significant correlation with true stroma stiffness
• CBI and TBI are the best screening tools for keratoconus and ectasia
• But true viscoelastic behavior cannot be measured with Corvis

To fully measure biomechanics, you need:
• ex vivo stress–strain tests
• Brillouin microscopy methods
• FEM modeling or AI-based reconstruction aids

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🎯 final summary

Corvis:
• ✔️ measures the dynamic response of the cornea
• ✔️ provides useful biomechanical indicators
• ✔️ is excellent for KC diagnosis and LASIK risk assessment
• ❌ does not directly measure the actual biomechanics of the tissue
• ❌ it is not possible to measure viscoelasticity and exact tissue moduli
Comparative text: Corvis position in measurement Biomechanics of the cornea

Corvis (Corvis ST) is one of the most advanced non-contact tools for evaluating corneal behavior, but it should be noted that this device does not directly measure the true and intrinsic biomechanics of the cornea. What Corvis does is record the dynamic response of the cornea to a standard air pulse; Therefore, the data it produces are actually functional and inferential indicators, not direct measurements of tissue properties.

Real corneal biomechanics include fundamental parameters such as Young's modulus, hysteresis, viscoelastic behavior, stress-strain properties, and collagen lamellar arrangement. These properties can only be directly measured by laboratory methods or technologies such as Brillouin microscopy. Corvis does not measure such parameters; Rather, it estimates relative stiffness and stability patterns from the appearance of the cornea when it changes shape.

However Corvis is a very valuable tool because it can provide biomechanical-clinical indicators: indicators such as SSI, CBI and TBI extracted from dynamic data and their combination with topography. These indices perform particularly well in diagnosing subclinical keratoconus, assessing the risk of post-LASIK ectasia, and monitoring the crosslinking effect. Therefore, the value of Corvis is that it measures clinically applicable biomechanics, not fundamental tissue biomechanics.

In other words:
Corvis shows the mechanical behavior of the cornea in practice, not the intrinsic properties of the tissue. The two are related, but not the same. This difference should be taken into account when interpreting data and making treatment decisions