A noninvasive clinical method to measure in vivo mechanical strains of the lamina cribrosa by optical coherence tomography.

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.