Biomechanics of the eye tunic, especially the sclera and the cornea

Abstract

Abstract Purpose The biomechanics of the cornea is not only important for IOP‐measurement but also for the outcome of refractive surgery. In recent studies, a thin cornea was also identified as an independent risk factor for the onset and progression of glaucoma. Besides, the rigidity of the sclera was proposed to play an important role in glaucoma and myopia. Methods An overview of biomechanical properties of the cornea and the sclera, based on own research results and on recent literature references, was performed. Results A stiffer cornea led to an overestimation of true IOP measured by applanation tonometry. The stiffness of the cornea increased by age compared to a decreasing corneal thickness. The Ocular Response Analyzer (ORA) measures the viscosity of the cornea. Paradoxically, ORA measurement revealed a reduction of corneal hysteresis with age which may indicate that corneal hysteresis is not equal to stiffness. In glaucoma the scleral and corneal rigidity increased in contrast to a reduced corneal hysteresis (CH) which may indicate that a damping effect of these tissues is reduced in glaucoma patients. Conversely, a more flexible and distensible sclera, lamina cribrosa and cornea were proposed to be beneficial to protect against experimentally induced IOP‐spikes. Conclusion A biomechanical concept of the eye tunic (cornea, sclera and lamina cribrosa) may further help to explain the relationship between IOP measurements, refractive surgery and glaucoma.