Biomechanical correlations between cornea and optic nerve head

Abstract

Purpose : A thin cornea is a potent risk factor for glaucoma. Although this discovery has been incorporated into clinical care, the connection between central cornea thickness (CCT) and glaucoma risk remains unexplained. It has been postulated that CCT may be a surrogate for biomechanical parameters of the posterior eye that impact the optic nerve head (ONH)’s stress/strain states. In this study, we explored the correlations of biomechanical responses between the cornea and the posterior eye to elevated intraocular pressure (IOP).

Methods : Inflation tests were performed in 10 pairs of human donor eyes. One eye of each pair was randomly assigned for cornea or ONH inflation (Fig. 1). Prior to cornea inflation, the cornea was treated with Poloxamer 188 to restore its physiological hydration following our published protocol [Clayson et al, Curr Eye Res, 2020]. CCT was measured using an ultrasound pachymeter. For either cornea or ONH inflation, the IOP was raised from 5 to 30 mmHg at 0.5 mmHg step in the whole globe and the tissue was imaged using a 50 MHz ultrasound probe (Vevo2100, VisualSonics). Correlation-based ultrasound speckle tracking was used to calculate tissue displacements. Strains were calculated using least square estimation. Associations of radial, tangential and shear strains at 30 mmHg between cornea and ONH or peripapillary sclera (PPS) were evaluated using Pearson correlations.

Results : Corneal shear strain was significantly correlated with ONH shear strain (R=0.652, p=0.041, Fig. 2A) and PPS shear strain (R=0.676, p=0.032, Fig. 2B). Other types of strains were not significantly correlated between cornea and ONH or PPS. CCT was not significantly correlated with any strains in ONH or PPS, and also not correlated with PPS thickness.

Conclusions : In this pilot study, we observed a positive correlation of shear strains between cornea and ONH/PPS. Although further studies in a larger sample size are needed, these results provided new evidence that cornea biomechanical responses may be correlated with the responses of the posterior eye which influence a patient's risk for glaucoma.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

Fig.1: Paired globes from the same donor were used to evaluate correlations of biomechanical responses between cornea (left) and ONH/PPS (right) to elevated IOP. Shaded area indicated the region scanned by ultrasound.

 

Fig.2: Corneal shear strain was positively correlated with ONH (A) and PPS (B) shear strain.