Under the Surface: Deformations in the Deep Lamina Cribrosa

Abstract

Purpose : Most in-vivo studies which involve the lamina cribrosa (LC) only focus on its anterior surface. In this study, we examine if microstructural deformations that occur in the anterior LC in response to acute IOP elevation are comparable to deformations within its depth.

Methods : In-vivo optic nerve head (ONH) spectral-domain OCT scans (Leica, Chicago, IL) were obtained from healthy adult Rhesus Macaques (8 eyes of 7 animals; 5 males, 2 females; ages 7.9-14.4 years) while IOP was increased and intracranial pressure (ICP) maintained at a baseline level. The anterior chamber of the eye and the lateral ventricle of the brain were cannulated, and gravity-based perfusion was used to control the pressures. ONH images were acquired at baseline, and two increased IOP settings: 30mmHg (H1) and 40-50 mmHg (H2). Scans were registered in 3D, and LC microstructure measurements (beam thickness, pore diameter, beam-to-pore ratio [BPR]) were obtained from shared regions and depths using a previously described segmentation algorithm. Microstructure parameters measured at the five most anterior enface planes of the LC were compared with an area in its depth that displayed the maximum absolute BPR change in response to IOP elevation.

Results : The depth of the region of maximal deformation differed substantially between eyes, ranging from 20 to 203 microns from the LC surface (Figure). The median absolute differences in BPR between the anterior LC surface and the area of maximal change in the depth were H1: 17.50% (±13.11) and H2: 19.45% (±16.50). Comparing the BPR measured at the LC surface to a location in which the microstructure deformed the most, the absolute percentage change was significantly higher than 10% at both IOP modulations (p=0.027). However, two principal patterns of response were noted: half of the eyes exhibited substantial microstructure deformation, whereas the rest showed only limited deformation. The difference in maximum deformation was significant between eyes that deformed and eyes that did not (H1: p= 0.001, H2: p=0.029). Overall BPR at normal IOP was significantly higher in eyes that exhibited substantial deformation (1.91 versus 1.45; p=0.037).

Conclusions : The LC deforms unevenly throughout its depth in response to IOP modulation. Therefore, a microstructural study of merely the anterior LC surface will not fully capture deformations that occur within it, especially in eyes with overall higher BPR.

This is a 2020 ARVO Annual Meeting abstract.