Real-time in vivo 2-D deformations of the optic nerve head using OCT imaging

Purpose:To quantify the real-time, in vivo, IOP-dependent mechanical deformations of the optic nerve head (ONH). Methods:The ONH of 7 eyes from 5 normal nonhuman primates (NHPs) was imaged with Spectralis OCT (Heidelberg Eng.). The OCT was equipped with research software that allowed continuous recording of a single B-scan over a period of 30 seconds at 5Hz while IOP was manipulated via anterior chamber manometry. At time=2s after the acquisition start the IOP was increased from 10 to 30 mmHg by switching a valve connecting 2 PBS manometry reservoirs. A collection of 150 vertical B-scans of the same cross-section (Fig. 1d) was processed with a custom algorithm that estimates the in-plane displacement field in each scan. The equivalent von Mises strain (StrainVM, Fig. 1b and 1c) was computed for each of the B-scans in the 4 regions shown in Fig. 1a. Results:The StrainVM was particularly high and quickly variable in the RNFL and near the PpScl - peripheral lamina junction, because of high bending deformations. The ONH tissues quickly deformed under increasing IOP but deformations steadily increased even after IOP reached 30 mmHg. A tight negative correlation between the ppScl and RNFL average strain was observed (p=0.0096, Fig. 1e). No significant correlations were observed for the strain in other regions. Conclusions:We estimated in vivo, real-time 2-D strain of the ONH tissues via OCT. The inverse correlation between the average strain in the peripapillary sclera and RNFL suggests that the stiffer sclera in the elderly and African descent populations may aggravate the biomechanical environment in the peripapillary axonal layer.