Abstract
Purpose :
To quantify and analyze regional variations of mechanical strains within the corneal stroma in human donor globes during intraocular pressure (IOP) elevation using high-frequency ultrasound speckle tracking.
Methods :
Ten globes from 9 human donors were obtained (age: 41-76 years old, 5 male and 4 female). Treatment with poloxamer 188 (3.5-4.25%) was used to return corneas to their physiological hydration as described previously (Clayson et al, EER, 2019). The globes were inflated from 5 to 30 mmHg in intervals of 0.5 mmHg. At each IOP level, an ultrasound scan was acquired using a 50 MHz probe (MS700, FujiFilm VisualSonics) from the central 9.73 mm of the cornea along the nasal-temporal meridian. Tissue displacements were calculated using ultrasound speckle tracking and strains were calculated using least squares estimation (Tang and Liu, JBME, 2012). The corneal stroma was divided into two regions, central and paracentral as shown in Fig 1a. The deformation of these two regions was compared using paired t-tests.
Results :
Strains measured at 30 mmHg were recorded for all 10 globes. Tangential strain in the corneal stroma was significantly larger in the paracentral (1.8±1.5%) than the central (0.40±1.1%) zone (p = 0.0022, Fig 1b, Fig 2a). Radial strain was not significantly different between these two zones (–2.1±1.9% vs –1.9±1.0%, p = 0.73, Fig 1c, Fig 2b). Shear strain magnitude was also not significantly different between zones (2.7±1.2% vs 3.1±2.2%, p = 0.49, Fig 1d, Fig 2c).
Conclusions :
High-frequency ultrasound elastography enabled quantification of the different types of deformation through corneal stroma, showing tangential stretch, radial compression, and shear during IOP elevation. The central cornea was subject to lower tangential stretch but similar radial compression and shear as compared to the paracentral cornea. The finding of lower tangential strain in the central cornea was consistent with previous reports of corneal surface deformation using optical methods.
This is a 2021 ARVO Annual Meeting abstract.