Corneal Biomechanics and Biomaterials

Abstract

The ability to clearly observe one's environment in the visible spectrum provides a tremendous evolutionary advantage in most of the world's habitats. The complex optical processing system that has evolved in higher vertebrate animals gathers, focuses, detects, transduces, and interprets incoming visible light. The cornea resides at the front end of this imaging system, where it provides a clear optical aperture, substantial refractive power, and the structural stability required to protect the fragile intraocular components. Nature has resolved these simultaneous design requirements through an exceedingly clever manipulation of common extracellular-matrix structural materials (e.g., collagen and proteoglycans). In this review, we (a) examine the biophysical and optical roles of the cornea, (b) discuss increasingly popular approaches to altering its natural refractive properties with an emphasis on biomechanics, and (c) investigate the fast-rising science of corneal replacement via synthetic biomaterials. We close by considering relevant open problems that would benefit from the increased attention of bioengineers.

Air Puff Induced Corneal Vibrations: Theoretical Simulations and Clinical Observations

“…In recent years, greater attention has been paid to the topic of corneal biomechanics. [1][2][3][4] In vitro experimental studies such as stress-strain tensile tests on corneal strips and inflation tests on the whole cornea have shown the viscoelastic, hyperelastic, and anisotropic features of both animal and human corneas. [5][6][7][8] Electromagnetic radiation scanning approaches are able to demonstrate how the collagen fibrils are spatially arranged within the stroma tissue, which have a great impact on the corneal biomechanical performance.…”

Corneal Tissue Engineering: Recent Advances and Future Perspectives

“…The adult human cornea measures between 12 and 13 mm in the horizontal and vertical diameters, 12 0.5 mm in thickness at the center and then progressively increases toward the sclera. 13 The cornea is an organ comprised of three distinct cellular layers, corneal epithelium, stroma, and endothelium, separated by two acellular collagenous interfaces referred to as Bowman's layer and Descemet's membranes (Fig. 1A).…”

“…(B) Collagen layers in the stroma provide mechanical tensile resistance, while a high concentration of small leucine-rich proteoglycans maintain the interfibrillar spacing required for transparency, and helping to regulate tissue hydration. 10,13 Adapted from Tan et al…”

“…13,16 The regular lamellar layering becomes increasingly random in the anterior stroma where more oblique branching and interweaving is observed. 19 Interlamellar branching is also more extensive in the corneal periphery than in the center.…”

“…27 The transparency of the cornea is determined by to the collagen interfibrillar spacing, regulated by the hydrophilic stromal proteoglycans, which are ultimately regulated by the tissue state of hydration, through the endothelium pump. 13 …”