The Strain Response to Intraocular Pressure Decrease in the Lamina Cribrosa of Patients with Glaucoma

Objective: To measure biomechanical strains in the lamina cribrosa (LC) of living human eyes with intraocular pressure (IOP) lowering. Design: Cohort study. Participants: Patients with glaucoma underwent imaging before and after laser suturelysis after trabecu-lectomy surgery (29 image pairs; 26 persons). Intervention: Noninvasive imaging of the eye. Main Outcome Measures: Strains in optic nerve head tissue and changes in depths of the anterior border of the LC. Results: Intraocular pressure decreases caused the LC to expand in thickness in the anterior-posterior strain (Ezz = 0.94 & PLUSMN; 1.2%; P = 0.00020) and contract in radius in the radial strain (Err = -0.19 & PLUSMN; 0.33%; P = 0.0043). The mean LC depth did not significantly change with IOP lowering (1.33 & PLUSMN; 6.26 mm; P = 0.26). A larger IOP decrease produced a larger, more tensile Ezz (P < 0.0001), greater maximum principal strain (Emax; P < 0.0001), and greater maximum shear strain (Tmax; P < 0.0001). The average LC depth change was associated with the Tmax and radial-circumferential shear strain (Erh; P < 0.02) but was not significantly related to tensile or compressive strains. An analysis by clock hour showed that in temporal clock hours 3 to 6, a more anterior LC movement was associated with a more positive Emax, and in clock hours 3, 5, and 6, it was associated with a more positive Tmax. At 10 o'clock, a more posterior LC movement was related to a more positive Emax (P < 0.004). Greater compliance (strain/DIOP) of Emax (P = 0.044), Tmax (P = 0.052), and Erh (P = 0.018) was associated with a thinner retinal nerve fiber layer. Greater compliance of Emax (P = 0.041), Tmax (P = 0.021), Erh (P = 0.024), and in -plane shear strain (Erz; P = 0.0069) was associated with more negative mean deviations. Greater compliance of Tmax (P = 0.055), Erh (P = 0.040), and Erz (P = 0.015) was associated with lower visual field indices. Conclusions: With IOP lowering, the LC moves either into or out of the eye but, on average, expands in thickness and contracts in radius. Shear strains are nearly as substantial as in-plane strains. Biomechanical strains are more compliant in eyes with greater glaucoma damage. This work was registered at ClinicalTrials.gov as NCT03267849. Ophthalmology Glaucoma 2023;6:11-22 & COPY; 2022 by the American Academy of Ophthalmology