Factors influencing chorioretinal biomechanical responses to IOP

Abstract

Purpose : A positive intraocular pressure (IOP) stretches the ocular shell and its inner lining: the chorioretinal tissue. Interestingly, chorioretinal folds occur under certain conditions despite the stretch created by IOP. In this study, we developed a computation model to determine which biomechanical factors most influenced chorioretinal stresses and strains and the implications for chorioretinal folds.

Methods : A computational model of the eye with two layers, the sclera and the chorioretina, was developed (Fig. 1A). Seven input factors including scleral/chorioretinal thickness, scleral/chorioretinal Poisson’s ratio, scleral/chorioretinal modulus, and IOP were independently varied within the reported ranges in the human eye (Fig. 1B). The mean in-plane stress and strain of the chorioretina were quantified as outcome measures. Input factors were ranked based on their relative influence on the outcome measures.

Results : Under all simulated conditions, the chorioretinal tissue experienced a positive in-plane strain but a negative in-plane stress (Fig. 1C, D). The 3 inputs that had largest influence on chorioretinal stress were, ranked in order, IOP, scleral modulus, and chorioretinal Poisson’s ratio (Fig. 2). The 3 inputs that had largest influence on chorioretinal strain were, ranked in order, scleral modulus, IOP, and chorioretinal Poisson’s ratio (Fig. 2). The mean in-plane stress within the chorioretina during IOP change from 10 to 30 mmHg was -1.15 to -3.46 kPa. The mean in-plane strain within the chorioretina was 1.13% to 0.14% when sclera modulus changed from 1 to 9 MPa.

Conclusions : The chorioretinal tissue experiences a negative in-plane stress which may underlie localized folding. This stress is strongly dependent on IOP, while sclera modulus has the largest effect on the in-plane strain. Changes in either may induce chorioretinal folds, consistent with clinical observations. These results provide new biomechanical insights into chorioretinal folds.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

 

Fig. 1: A. Model schematics. B: Baseline and ranges of input factors. C, D: Effects of input factors on in-plane stress and strain within chorioretinal tissue. X-axis was scaled linearly from minimum (0) to maximum (1) of each input factor.

 

Fig. 2: Relative influence of each input factor on chorioretinal stress or strain, showing IOP has the largest influence on stress while sclera modulus has the largest influence on strain.