Quantification of iris elasticity using acoustic radiation force optical coherence elastography

Abstract

Careful quantification of the changes in biomechanical properties of the iris can offer insight into the pathophysiology of some ocular diseases. However, to date there has not been much information available regarding this subject because clinical detection for iris elasticity remains challenging. To overcome this limitation, we explore, for the first time to our knowledge, the potential of measuring iris elasticity using acoustic radiation force optical coherence elastography (ARF-OCE). The resulting images and shear wave propagation, as well as the corresponding shear modulus and Young’s modulus from ex vivo and in vivo rabbit models confirmed the feasibility of this method. With features of noninvasive imaging, micrometer-scale resolution, high acquisition speed and real-time processing, ARF-OCE is a promising method for reconstruction of iris elasticity and may have great potential to be applied in clinical ophthalmology with further refinement.

In vivo non‐contact measurement of human iris elasticity by optical coherence elastography

“…The method employed was indirect and thus, is unsuitable for obtaining the absolute value of the elastic modulus. Zhu et al [37] evaluated the elasticity of the rabbit iris using ARF OCE. The excitation system they used contained an ultrasound transducer, which still required contact with the eyeball to generate shear waves within the iris.…”

“…where E is Young's modulus, v is Poisson's ratio (because the iris is considered an incompressible material under small strains, v = 0.49), and ρ is the density of the iris (ρ = 1250 kg/m 3 according to the literature [22,37]).…”

“…Thus, previous studies investigating the iris mechanical properties have been mostly ex vivo measurements. Recently, acoustic radiation force optical coherence elastography (ARF-OCE) was reported to evaluate the iris elasticity of rabbit eyeballs in vivo [37]. However, the excitation system used an ultrasound transducer, which needed to contact the eyeball to generate a mechanical wave within the iris.…”

Assessing Porcine Iris Elasticity and Mechanical Anisotropy with Optical Coherence Elastography

“…In addition to abnormal morphological changes, the iris also undergoes natural variations due to its function in the eye (contraction and expansion) [11]. Several studies have shown interest in determining the biomechanical properties of the iris, under different conditions (in vivo or ex vivo) using animal models [12][13][14] or human volunteers [11], using different techniques such as Atomic Force Microscopy (AFM) [15], Optical Coherence Tomography (OCT) [9], and Optical Coherence Elastography (OCE) [11,14,16]. Although AFM showed a high capacity to determine the stiffness of the iris, it had several limitations.…”

“…Thus, OCE is rapidly gaining popularity for assessing tissue biomechanical properties [22,23]. OCE can describe the biomechanical differences among the different tissues of the same organs, such as the detailed description of the biomechanical properties of the inner structure of the eye [20,[24][25][26], including the iris [11,16]. However, these studies have not investigated the effects of intraocular pressure (IOP) changes on the stiffness of the iris.…”