Biomechanical properties of retina and choroid: a comprehensive review of techniques and translational relevance

Abstract

Studying the biomechanical properties of biological tissue is crucial to improve our understanding of disease pathogenesis. The biomechanical characteristics of the cornea, sclera and the optic nerve head have been well addressed with an extensive literature and an in-depth understanding of their significance whilst, in comparison, knowledge of the retina and choroid is relatively limited. Knowledge of these tissues is important not only to clarify the underlying pathogenesis of a wide variety of retinal and vitreoretinal diseases, including age-related macular degeneration, hereditary retinal dystrophies and vitreoretinal interface diseases but also to optimise the surgical handling of retinal tissues and, potentially, the design and properties of implantable retinal prostheses and subretinal therapies. Our aim with this article is to comprehensively review existing knowledge of the biomechanical properties of retina, internal limiting membrane (ILM) and the Bruch's membrane-choroidal complex (BMCC), highlighting the potential implications for clinical and surgical practice. Prior to this we review the testing methodologies that have been used both in vitro, and those starting to be used in vivo to aid understanding of their results and significance.

Fig. 1. Biomechanical in vitro test methods.

Schematic illustration of deformation modes experienced in commonly used test methods to characterise the mechanical properties of ocular tissues showing a uniaxial tension, b biaxial tension, c inflation and d atomic force microscopy.

Fig. 2. Stress–strain curve for soft tissues.

Schematic illustration of a typical non-linear stress-strain curve for soft biological tissue showing the points at which the toe modulus, heel modulus, yield strength and ultimate yield strength are calculated.

Fig. 3. Retina and choroid.

Schematic diagram of retinal layers, Bruch’s membrane and choroid.