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

ObjectiveTo measure mechanical strain of the lamina cribrosa (LC) after intraocular pressure (IOP) change produced one week after a change in glaucoma medication. DesignCohort study. ParticipantsAdult glaucoma patients (23 eyes, 15 patients) prescribed a change in IOP-lowering medication. InterventionNon-invasive optical coherence tomography (OCT) imaging of the eye. Main OutcomesDeformation calculated by digital volume correlation of OCT scans of the LC before and after IOP lowering by medication. ResultsAmong 23 eyes, 17 eyes of 12 persons had IOP lowering [&ge;] 3 mmHg (reduced IOP group) with tensile anterior-posterior Ezz strain = 1.0% {+/-} 1.1% (p = 0.003) and compressive radial strain (Err) = -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: Emax = 1.7% {+/-} 1.0% and{Gamma} max = 1.4% {+/-} 0.7%, respectively (both p<0.0001 versus zero). Reduced IOP group strains Emax and{Gamma} max were significantly larger with greater %IOP decrease (<0.0001, <0.0001). The compliance of the Ezz, Emax, and{Gamma} 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[&ge;]0.02). Strains were unrelated to age (all p[&ge;]0.088). In reduced IOP eyes, mean LC anterior border posterior movement was only 2.05 m posteriorly (p=0.052) and not related to % IOP change (p=0.94, random effects models). Only Err was significantly related to ALD change, becoming more negative with greater posterior LC border change (p=0.015). ConclusionLC 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 RegistrationClinicalTrials.gov Identifier: NCT03267849