IN VIVO BIOMECHANICAL STRAIN RESPONSE OF THE LAMINA CRIBROSA TO INTRAOCULAR PRESSURE CHANGE AS A RESULT OF GLAUCOMA MEDICATION CHANGE

Abstract

The aim of the present pilot study was to evaluate the feasibility of a method for characterizing the short-term, in vivo biomechanical response of the lamina cribrosa (LC) in the eyes of patients starting glaucoma medication as a potential biomarker for primary open angle glaucoma (POAG). Radial optical coherence tomography (OCT) image volumes were acquired and intraocular pressure (IOP) was measured for 23 eyes from 15 patients before starting glaucoma medication and after a duration of 7.3 ± 1.4 days. Pre- and post-treatment image volumes were compared using digital volume correlation (DVC) to determine the anterior LC (ALC) strains and anterior LC depth (ALD) change. After the one-week treatment period, IOP decrease caused significant tensile Ezz greater than baseline error, compressive Err greater than baseline and correlation error, and small but significant posterior ALD change in Group 1 (eyes which had an IOP decrease of at least 4 mmHg). In Group 2 (eyes with 0-1 mmHg IOP change), there was a significant tensile Ezz, however its magnitude was approximately three times smaller than that of the Group 1 eyes and it did not exceed baseline or correlation error. Strain magnitudes were more highly correlated with percent IOP decrease than IOP decrease. Strains did not vary by quadrant of the LC and did not relate to ALD change. ALD change did not increase with increased IOP decrease. Strains and strain compliance increased with decreasing mean deviation (MD) and visual field index (VFI), but decreased with thinner average retinal nerve fiber layer (RNFL). Strains, strain compliance response, ALD change, RNFL, MD, and VFI were not significantly related to patient age. The results of the present study suggest the current method is a promising method for measuring repeatable LC strains and depth change in the eyes of patients subjected to IOP change as a result of glaucoma medication change.