A noninvasive clinical method to measurein vivomechanical strains of the lamina cribrosa by optical coherence tomography

ABSTRACT Objective To measure mechanical strain of the lamina cribrosa (LC) after intraocular pressure (IOP) change produced one week after a change in glaucoma medication. Design Cohort study. Participants Adult glaucoma patients (23 eyes, 15 patients) prescribed a change in IOP-lowering medication. Intervention Non-invasive optical coherence tomography (OCT) imaging of the eye. Main Outcomes Deformation calculated by digital volume correlation of OCT scans of the LC before and after IOP lowering by medication. Results Among 23 eyes, 17 eyes of 12 persons had IOP lowering ≥ 3 mmHg (reduced IOP group) with tensile anterior-posterior E zz strain = 1.0% ± 1.1% (p = 0.003) and compressive radial strain ( E rr ) = -0.3% ± 0.5% (p=0.012; random effects models accounting inclusion of both eyes in some persons). Maximum in-plane principal (tensile) strain and maximum shear strain in the reduced IOP group were: E max = 1.7% ± 1.0% and Γ max = 1.4% ± 0.7%, respectively (both p<0.0001 versus zero). Reduced IOP group strains E max and Γ max were significantly larger with greater %IOP decrease (<0.0001, <0.0001). The compliance of the E zz , E max , and Γ max strain response, defined as strain normalized by the IOP decrease, were larger with more abnormal perimetric mean deviation or visual field index values (all p≥0.02). Strains were unrelated to age (all p≥0.088). In reduced IOP eyes, mean LC anterior border posterior movement was only 2.05 μm posteriorly (p=0.052) and not related to % IOP change (p=0.94, random effects models). Only E rr was significantly related to ALD change, becoming more negative with greater posterior LC border change (p=0.015). Conclusion LC mechanical strains can be effectively measured by changes in eye drop medication using OCT and are related to degree of visual function loss in glaucoma. Trial Registration ClinicalTrials.gov Identifier: NCT03267849