Corneal biomechanics plays an important role in determining the eye's structural integrity, optical power and the overall quality of vision. Common conditions that manifest abnormal corneal biomechanics, such as keratoconus and post-LASIK ectasia affect millions of people and often necessitate corneal transplantation. Corneal biomechanics also plays an increasingly recognized role in the post-operative results of therapeutic and refractive corneal surgery procedures, affecting the predictability, quality and stability of final visual outcomes. A critical limitation to increasing our understanding of how corneal biomechanics controls corneal stability and refraction is the lack of non-invasive technologies that microscopically measure the corneal structure and local biomechanical properties, such as corneal elasticity within the 3D space. We hypothesize that by measuring the movement of a femtosecond laser generated cavitation bubble as it interacts with an acoustic radiation force, we can determine local values for an individual cornea's Young's modulus, without altering its structure and function. We also hypothesize that the inhomogeneous elastic properties of the cornea are strongly influenced by the microstructural organization of collagen lamellae, and that corneas with abnormal biomechanics also may be associated with an abnormal organization of corneal lamellae. Finally, we hypothesize that based on the elasticity and microstructural data for a particular cornea, a specific finite element model (FEM) can be constructed that accurately describes and predicts its biomechanical behavior. To test our hypothesis we plan to develop a bubble-based, acoustic radiation force elastic microscope (ARFEM) and show that it can be used noninvasively to develop a high resolution 3D corneal elasticity map. We will then correlate local variations in corneal elasticity with the microstructure observed by femtosecond laser based second harmonic imaging microscopy (SHIM). We will also investigate biomechanically disordered corneas with both, ARFEM and SHIM, and correlate their elasticity maps with microstructural observations. We will construct a FEM based on the measured ARFEM and SHIM data and show that this model accurately predicts biomechanical behavior for a particular cornea. Finally we will demonstrate in a live rabbit model, that both, ARFEM and SHIM can be performed safely in vivo without tissue damage or harmful effects to the eye. The successful completion of this project will provide experimental evidence that corneal elasticity maps and microstructure can be measured in vivo noninvasively. It will also provide support for the theory that corneal elasticity is influenced by the collagen microstructure, and that the biomechanical behavior of a cornea characterized by ARFEM and SHIM can be accurately predicted by individualized finite element modeling. The results of this project will increase our understanding of corneal biomechanics and its dependence on collagen microstructure and may provide the basis for a novel tool that could be helpful in diagnosing, preventing or treating increasingly common corneal diseases such as keratoconus and post-LASIK ectasia.
We introduce novel noninvasive methods to define spatial distribution of elastic properties and collagen microstructure of individual corneas. The correlation of these functional and structural measurements in healthy eyes will be compared with those that either have common corneal disorders (such as keratoconus and post-LASIK ectasia), or are at risk for them. The results of this project will improve our understanding of corneal biomechanics and its dependence on the collagen microstructure, providing a basis for novel diagnostic instruments and eventual therapeutic modalities for the millions of people that are at risk for severe visual loss from these conditions.
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