Abstract
Purpose :
The peripapillary sclera (PPS) strongly influences the biomechanical responses of the optic nerve head (ONH). The peripapillary scleral flange (PSF) is the connecting point between PPS and ONH. It is also the bridge posterior ciliary artery branches traverse to reach the anterior ONH. In this study, we used high-frequency ultrasound to quantify the 3D mechanical response of the PPS and analyzed the distinct response of the PSF in one eye.
Methods :
Inflation tests were performed in 16 human donor (20-78 years old) globes while raising intraocular pressure (IOP) from 15 to 30 mmHg at 2-5 mmHg intervals. A 3D volume centered at the ONH was scanned at each pressure step using a 50MHz ultrasound probe (Vevo2100, VisualSonics). A correlation-based 3D speckle tracking algorithm was used to compute tissue displacements. Distributed and average radial (εrr), meridional (εφφ), circumferential (εθθ), and shear (εθr, εφr and εθφ) strains were calculated in the PPS region. One volume with high image quality was segmented to mark the Bruch’s membrane opening (BMO) and delineate the PSF region as the PPS within 400 μm distance from the BMO (Fig. 1).
Results :
At 30 mmHg, PPS normal strains were -3.39±1.14%, 0.23±0.17%, and 0.14±0.10% for εrr, εφφ, and εθθ, respectively. PPS shear strains were 1.25±0.38%, 1.29±0.41%, and 0.55±0.13% for εθr, εφr, and εθφ, respectively. PPS deformation was heterogenous through volume. Localized high strains were frequently observed near the ONH-PPS boundary. 3D strain maps in the PSF of one eye are presented in Fig. 2. Compared to PPS, PSF had larger strains for all six strains. Particularly, PSF radial strain was 1.9X higher and out-of-plane shears were over 2.2X higher than PPS strains of the same eye.
Conclusions :
The PSF is a strategically important biomechanical structure as the anchor to the laminar cribrosa (LC) and bridge for ONH blood supply. Our results showed that this region is where mechanical insult is highly concentrated during IOP elevation, possibly underlying glaucomatous damage such as disc hemorrhage and LC tear.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.