Analysis of IOP-induced lamina cribrosa displacement and strain using digital volume correlation of optical coherence tomography images

Abstract

Purpose : To quantify the 3-dimensional (3D) deformation and strains of the lamina cribrosa (LC) induced by intraocular pressure (IOP) change produced by wearing goggles or by suturelysis after trabeculectomy in optical coherence tomography (OCT) images.

Methods : We analysed 24 radial OCT optic nerve head (ONH) scans in 10 eyes of 8 glaucoma suspects and patients (mild to moderate damage) before and 15-30 minutes after mean IOP change=9.0±7.2 mmHg induced by either tight swim goggles or suturelysis. A digital volume correlation (DVC) algorithm was used to calculate the 3D displacements of the ONH tissues between images at higher and lower IOP. The LC anterior border, choroidal-scleral interface, and BM position were manually segmented in each pre-IOP change image. The anterior LC included the visible tissue from its anterior border to a 250 µm depth posterior. Anterior LC depth (ALD) was defined as the mean distance from Bruch’s membrane opening to the LC anterior border. Average strains in LC, retina, and choroid, and ALD changes were calculated from DVC displacements. DVC successfully correlated 75% of LC area and mean estimated strain error was 0.37%.

Results : When correlating images from higher IOP to lower IOP, there was decreased antero-posterior LC compression (significantly positive antero-posterior strain, E_ZZ). Ezz was highest in choroid (1.39%, p=0.03), intermediate in LC (0.53%, p=0.0003), and lowest in retina (0.23%, p=0.14). Mean ALD was significantly deeper at the lower IOP level (2.1±2.4 µm, p=0.023; deeper in 8/10 eyes). Eyes with greater ALD change had larger E_max strains (linear model, r²=0.49, p=0.02). E_ZZ strain was significantly larger with greater IOP change (linear model, r²=0.44, p=0.038). E_ZZ strain in central LC was twice that of peripheral LC (mean paired difference: 0.32% (95% CI: 0.14, 0.49), p=0.003), while central vs. peripheral ALD change were not significantly different.We will present quadrant and clock hour ALD and strain data, and correlation to nerve fiber layer thickness.

Conclusions : A DVC method to measure strain from OCT shows ALD is often shallower at higher IOP, while LC tissues are more compressed. LC strain and ALD position can each contribute biomarker information to predict glaucoma susceptibility..

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Single 2D ONH scan, strain color coded by right scale.