Refractive Index-Matching to Improve Polarization-Resolved Second Harmonic Imaging of the Human Cornea in Depth

The human cornea is the outermost anterior portion of the eye and is 500–600 μm thick. Its transparency and refractive properties are closely related to the highly organized structure of the stroma, which consists of several hundreds 1-3 μm thick lamellae that are stacked parallel to the corneal surface. These lamellae are composed of well-aligned and regularly packed thin collagen fibrils (approximately 30 nm in diameter) that are oriented mainly along the inferior-superior and the nasal-temporal axes. However, this anisotropic hierarchical organization and its relationship to the biomechanical response of the cornea have been poorly characterized due to limitations of conventional techniques.