No abstract

The lamina cribrosa (LC) is a connective tissue in the optic nerve head (ONH). The objective of this study was to measure the curvature and collagen microstructure of the human LC, compare for the effects of glaucoma and glaucoma optic nerve damage, and investigate the relationship between the structure and pressure-induced strain response of the LC in glaucoma eyes. Previously, the posterior scleral cups of 10 normal eyes and 16 diagnosed glaucoma eyes were subjected to inflation testing with second harmonic generation (SHG) imaging of the LC and digital volume correlation (DVC) to calculate the strain field. In this study, we applied a custom microstructural analysis algorithm to the maximum intensity projection SHG images to measure features of the LC beam and pore network. We also estimated the LC curvatures from the anterior surface of the DVC-correlated LC volume. Results showed that the LC in glaucoma eyes had larger curvatures (p ≤ 0.03), a smaller average pore area (p = 0.001), greater beam tortuosity (p < 0.0001), and more isotropic beam structure (p = 0.01) than in normal eyes. The difference measured between glaucoma and normal eyes may indicate remodeling of the LC with glaucoma or baseline differences that contribute to the development of glaucomatous axonal damage.

Objective: To measure the active remodeling of the lamina cribrosa (LC) years after IOP lowering by suturelysis. Design: Cohort study. Participants: Glaucoma patients were imaged 20 minutes after laser suturelysis following trabeculectomy surgery and at their follow-up appointment 1-4 years later (16 image pairs; 15 persons). Intervention: Non-invasive optical coherence tomography (OCT) imaging of the eye. Main Outcomes: Deformation calculated by correlating OCT scans of the LC immediately after IOP lowering by suturelysis and those acquired years later (defined as follow-up strain). Results: Mean LC follow-up strain in the anteroposterior direction (Ezz) was 14.0 ± 21.3% (mean, standard deviation, p=0.03), while the LC anterior border moved 60.9 ± 54.6 μm into the eye (p=0.0006) on long-term, maintained IOP lowering. Ezz at follow-up was 14 times larger than the direct Ezz response to IOP lowering by suturelysis. There was a significant association between larger LC anterior movement and greater Ezz (p=0.004) at follow-up. Thinner retinal nerve fiber layer (RNFL) at suturelysis was associated with greater follow-up Ezz (p=0.04). Worsening visual field indexes during follow-up were associated with greater LC widening (positive remodeling Eθθ, p=0.02). Eyes with a greater counterclockwise twist (positive Eθz) at suturelysis had greater reversal clockwise twist at follow-up (negative remodeling Eθz, p=0.007). Conclusion: Follow-up strains and LC border position changes measured years after IOP lowering are far larger than the immediate strain response and LC border movement response to IOP lowering and indicate dramatic remodeling of the LC anatomical structure caused by IOP lowering and glaucoma progression. The remodeling includes a substantial increase in LC thickness and movement into the eye. Eyes with greater direct strain response to IOP-lowering strains, greater glaucoma damage at suturelysis, and greater worsening of visual field at follow-up experienced greater remodeling.

Objective To measure strain values and their association with intraocular pressure (IOP) change across five posterior eye regions in glaucoma patients. Design Cohort study. Participants Glaucoma patients who were imaged with optical coherence tomography (OCT) prior to and after laser suturelysis following trabeculectomy surgery (29 image pairs, 26 persons) Intervention Noninvasive imaging of the eye. Main Outcomes Strain values in eye regions. Results Mean strains were lowest in the retina and highest in the prelaminar neural tissue (PLNT) for Emax, Γmax, and Ezz. The values of Emax in the anterior lamina cribrosa (ALC) and sclera were significantly related (P=0.0094, linear regression). Higher axial strain (Ezz) was significantly associated with greater IOP decrease in the ALC, PLNT, and retina (P<0.05). Higher Γmax and Emax strains were significantly associated with greater IOP decreases across all 5 eye regions. ALC and PLNT had negative median radial (Err) compliance, while sclera had positive Err compliance (P=0.017). Emax and Γmax strains of the ALC were significantly and positively associated with these strains in the other 4 regions (P<0.005). Likewise, the Ezz of ALC had a significant positive relationship with the other 4 regions (P<0.05). Conclusions Regional strains in the optic nerve head zone can be effectively measured using OCT and are related to the magnitude of IOP change. Strains were largest in PLNT and ALC and were smallest in retina. The sclera and choroid on average expand radially and circumferentially indicating a volume increase with IOP lowering.