A microstructurally-based finite element model of the incised human cornea

Area of Science:

• Biomechanics of the eye
• Ophthalmic surgery modeling

Background:

• The cornea's structural behavior is primarily governed by stromal properties.
• Corneal flexural and shear rigidities are negligible compared to its membrane rigidity.
• Collagen fibrils in the stroma resist tensile forces, with limited load transfer due to low ground substance shear modulus.

Purpose of the Study:

• To develop a mechanical model of the human cornea for simulating surgical procedures like radial keratotomy.
• To investigate the anisotropy and inhomogeneity induced by incised collagen fibrils.
• To analyze the factors influencing radial keratotomy outcomes.

Main Methods:

• Proposed a mechanical model of the cornea as a thick membrane shell.
• Developed a linear elastic, time-independent constitutive model for the incised cornea.
• Employed a geometrically non-linear finite element membrane shell formulation for small strains with moderate rotations.

Main Results:

• The model quantifies anisotropy and inhomogeneity in corneal membrane rigidity after incisions.
• Numerical examples demonstrate the effectiveness of the constitutive model and finite element formulation.
• Investigated the impact of elastic moduli, incision depth, optic zone size, number/position of incisions, and intraocular pressure on refractive outcomes.

Conclusions:

• The proposed model accurately predicts immediate postoperative corneal power shifts after radial keratotomy.
• Results show excellent correspondence with expert surgeon predictions.
• The model provides a quantitative tool for understanding and optimizing radial keratotomy outcomes.