Spatially heterogeneous corneal mechanical responses before and after riboflavin–ultraviolet-A crosslinking

Abstract

PURPOSE To determine the heterogeneous through-thickness strains in the cornea at physiologic intraocular pressures before and after corneal collagen crosslinking (CXL) using noninvasive ultrasound. SETTING Department of Biomedical Engineering, Ohio State University, Columbus, Ohio, USA. DESIGN Experimental study. METHODS Sixteen paired canine corneoscleral shells were divided into 2 groups. The CXL group completed a standard CXL protocol using riboflavin–ultraviolet-A (UVA) irradiation. The control group was given an identical treatment except UVA irradiation. Ultrasound scans (at 55 MHz) of the cornea were obtained before and after treatment as the corneoscleral shell was inflated from 5 mm Hg to 45 mm Hg to calculate the distributive through-thickness strains in the cornea. The mean radial and tangential strains of the whole cornea layer, as well as those of the anterior, middle, and posterior thirds of the cornea, were compared before and after treatment in the control group and CXL group using linear mixed models with repeated measures. RESULTS Significant reductions in tangential and radial strains occurred in the CXL group (P=.003 and P=.0025, respectively) but not the control group (P=.08 and P=.63, respectively). The anterior third had the smallest strains in all pretreated corneas (P<.001) and posttreated corneas (CXL group, P=.023; control group, P=.01). CONCLUSIONS Ultrasound speckle tracking showed heterogeneous strain distributions through the cornea and confirmed that CXL results in a stiffer corneal response (ie, smaller strains during physiologic loadings). This technique may provide a clinical tool to quantify the biomechanical effects of CXL. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Assessing the effects of riboflavin/UV-A crosslinking on porcine corneal mechanical anisotropy with optical coherence elastography

“…Our results showed that the overall Young's modulus of the porcine cornea increased by ~154%, which is similar to the ~180% increase in Young's modulus at a strain of 0.06 as measured by strip extensiometry [12]. However, SSI has shown an increase in the corneal Young's modulus between 236% and 760% after CXL [47], inflation testing showed an increase of ~59% in Young's modulus [48], and ultrasound elastography (USE) showed a ~55% decrease in tangential strain [49]. Our own previous work has shown an increase of ~200% and ~630% as measured by OCE [27,50], showing that there is a wide variance in the literature of the changes in the biomechanical properties of the porcine cornea after CXL due to various factors such as age, testing conditions, measurement technique, and method for material parameter quantification.…”

Optical coherence elastography assessment of corneal viscoelasticity with a modified Rayleigh-Lamb wave model

“…Nevertheless, the stiffness quantified by the mRLFE was similar to our previous work using OCE measurements and/or numerical modeling (Han et al, 2015b; Han et al, 2016; Singh et al, 2016c; Singh et al, 2015). The change in corneal stiffness due to CXL is also quite varied in the literature, ranging from an increase of few hundred percent as measured by strip extensiometry and supersonic shear wave imaging (Cherfan et al, 2013; Nguyen et al, 2012; Wollensak et al, 2003b) to an increase of approximately 50% as assessed by inflation testing and ultrasound elastography (Kling et al, 2010; Palko et al, 2014). Once again, these studies were conducted under different conditions.…”

“…Additionally, the mRLFE assumes the sample is isotropic, which is also not strictly true of the cornea (Elsheikh and Alhasso, 2009; Elsheikh et al, 2008b; Nguyen et al, 2014; Pinsky et al, 2005; Singh et al, 2016c). Lastly, the mRLFE assumes the sample is homogeneous but the elasticity of the cornea and stiffening effects of the CXL are not homogeneous depth-wise (Beshtawi et al, 2016; Dias et al, 2015; Palko et al, 2014; Scarcelli et al, 2013; Seifert et al, 2014; Wang and Larin, 2014a). This may be a reason for relatively poor fitting of the mRLFE, particularly in the case of CXL samples as seen in Figure 3(b).…”

Corneoscleral stiffening increases IOP spike magnitudes during rapid microvolumetric change in the eye

“…Johnson et al’s study mounted the corneal buttons on a rigid artificial anterior chamber and thus may not accurately reflect the in vivo corneal inflation under IOP elevations. We have previously observed significant corneal deformation especially through-thickness compression using high-frequency ultrasound speckle tracking (Palko et al, 2014) in eyes mounted at the posterior sclera preserving the corneal boundary conditions. Other corneal inflation studies have reported similar results showing significant corneal deformability during inflation (Boyce et al, 2008; Kling et al, 2010).…”