Ophthalmology

Refractive interventions are widespread techniques for vision correction such as myopia or astigmatism. The cornea of the patient is reshaped by surgical intervention like incisions and laser ablation of stromal tissue. The amount of tissue to remove is traditionally estimated based on experimental nomograms or geometrical approaches. Unfortunately, the change of corneal power is frequently over- or under-estimated.

We proposed an opto-mechanical simulation framework to quantify the optical outcome induced by alteration of the corneal biomechanics. This numerical framework was used to perform personalized simulations of different surgical procedures such as corneal ring implantation and arcuate keratotomy. For example, arcuate keratotomy is a surgical technique used to correct astigmatism following cataract interventions. Our numerical simulation framework could estimate the outcome of different planning options before the surgery. Based on this numerical approach, we were also able to propose optimization algorithms to automatically determine the surgical parameters optimal for each specific patient. The patient-specific optimization of the surgery proved to better control the outcome of the intervention, leads to more reliable postoperative astigmatism, and limits the risks of overcorrection.

Depth-dependent biaxial characterization of corneal stroma

More than 185,000 corneal transplants are performed each year, but more than half of the world's population does not have access to donor corneas, compromising patient care and research opportunities. Comprehensive knowledge of corneal biomechanics is critical to improving the treatment of diseases such as keratoconus, corneal ectasia and ulcers to reduce the need for corneal transplants.

We investigate the biomechanical properties of the corneal stroma by biaxial tensile testing at different corneal depths: anterior, central and posterior (Fig. 2). Our results provide a detailed characterization of the mechanical behavior of the corneal stroma under a load that resembles the physiological situation and show a significant decrease in stiffness from the anterior to the posterior corneal layers, probably due to differences in the alignment of collagen fibers. This research provides valuable data for the development of numerical models of corneal biomechanics that can contribute to a better understanding of current treatments and pathologies.

These models can also drive innovation in corneal repair and reconstruction techniques and support the development of new solutions for corneal surgery and biomaterials.

Hydrogel microinjections for vision correction

By 2050, it is estimated that more than 5 billion people will be affected by refractive vision disorders, including presbyopia, myopia and astigmatism.

Although laser eye surgery offers correction by reshaping the cornea through tissue removal, this method weakens the corneal structure and can lead to complications. In addition, patients with thin corneas or high refractive errors are often unsuitable for laser-based procedures. To address this, we introduce an innovative treatment that uses hydrogel injections into the cornea to correct vision without compromising the integrity of the cornea.

Our method is a viable alternative for patients who are not candidates for conventional laser treatment, including patients with conditions such as keratoconus. Unlike laser correction, this technique restores vision through precise hydrogel microinjections that create customized implants directly in the cornea, reshaping and strengthening it at the same time. This approach eliminates the need for external implants as the cornea is dynamically adjusted during the controlled injection process. Our ex vivo studies in animal models have shown consistent vision correction, with refractive adjustments of over 15 diopters (Fig. 3).

Quantifying  the mechanical effects of corneal cross-linking using optical coherence elastography

In vivo quantification of corneal biomechanics is crucial for understanding treatment outcomes, but remains a major challenge. To solve this problem, we have used Optical Coherence Elastography (OCE), a technique that can capture dynamic mechanical changes in the cornea at high resolution. OCE has a high spatial resolution, and we were able to investigate the strain induced in the cornea by the osmotic effects of different preservative media and by corneal cross-linking (CXL). Experiments in porcine eyes showed that different preservation media led to distinct strain patterns, with deswelling or swelling occurring depending on the tonicity of the medium. Additionally, in eyes treated with CXL, OCE detected a marked deswelling in the anterior stroma after UV irradiation (Fig. 4), indicating increased tissue rigidity.

These biomechanical changes could explain the refractive changes observed clinically in the patients. To further investigate and predict these effects, a finite element model (FEM) was validated to simulate the refractive outcomes of CXL in the clinical setting. Data from two cohorts of patients undergoing standard or customized CXL were compared with the FEM predictions. Customized CXL resulted in greater corneal flattening, which was accurately predicted by the FEM simulations. Together, OCE and FEM provide powerful tools for optimizing CXL treatment planning and understanding corneal biomechanics.