Lamina Cribrosa Strain as a Glaucoma Prognostic Factor: The STRAIN Study Methodology and Initial Outcomes
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Objective
To estimate the lamina cribrosa (LC) strain response to intraocular pressure (IOP) change in open angle glaucoma (OAG) patients and examine associations between LC strain and demographic and clinical characteristics relevant to OAG in an ongoing longitudinal study.
Design
Cohort study
Participants
Adult patients with OAG (205 eyes of 119 patients)
Methods
The STRAIN study is an ongoing longitudinal study designed to determine whether LC biomechanical strain is associated with present, prior, and future OAG damage. In this initial analysis, patients either temporarily stopped ≥1 eye drop, initiated an eye drop, or underwent selective laser trabeculoplasty to produce IOP change. Optical coherence tomography (OCT) scans of the optic nerve head (ONH) acquired before and up to several weeks after IOP change were analyzed using digital volume correlation (DVC) to estimate LC strain. Strain measurements were compared with age, race, sex, axial length, central corneal thickness (CCT), corneal hysteresis, optic disc area, years of known OAG, retinal nerve fiber layer (RNFL) thickness, and visual field mean deviation (MD).
Main Outcome Measures
LC strain estimated by DVC from OCT scans acquired before and after IOP alteration.
Results
Axial LC strain ( Ezz ) was tensile with IOP decrease and compressive with IOP increase. Maximum principal strain was tensile (mean E max = 1.09%), and maximum shear strain was positive (mean Γ max = 1.16%) in the radial-axial plane. Both increased quadratically with the IOP change. Older age was significantly related to greater tensile circumferential strain ( p = 0.02) and lower Γ max ( p = 0.01). Sex, CCT, corneal hysteresis, and optic disc area were not significantly associated with LC strain. In combined multivariable models adjusting for IOP change, demographics, and accounting for correlations between eyes from the same patient, eyes with thinner inferior-quadrant RNFL had smaller Γ max for a given IOP change ( p = 0.02).
Conclusions
LC strain in patients with OAG is associated with the degree of neuronal loss, age, and axial length, supporting a relationship between the LC biomechanical response and factors relevant to glaucomatous damage.
