A Noninvasive Clinical Method to Measure in Vivo Mechanical Strains of the Lamina Cribrosa by OCT

Objective: To measure mechanical strain of the lamina cribrosa (LC) after intraocular pressure (IOP) change produced 1 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: Noninvasive OCT imaging of the eye. Main Outcome Measures: 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 as follows: E_max = 1.7% ± 1.0% and Γ_max = 1.4% ± 0.7%, respectively (both P < 0.0001 vs. zero). Reduced-IOP group strains E_max and Γ_max were significantly larger with greater % IOP decrease (P < 0.0001 and P < 0.0001, respectively). The compliances of the E_zz, E_max, and Γ_max strain responses, 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 anterior lamina depth change, becoming more negative with greater posterior LC border change (P = 0.015). Conclusions: Lamina cribrosa 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. Financial Disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.