Abstract
Purpose :
Changes in stiffness of the micro-environment of the ONH region is a significant risk factor for onset and progression of glaucoma (Hopkins A, et al, Am J Physiol Cell Physiol 2020) . Deformation of the ONH or its strain is dependent on the elastic modulus of the constituent elements of the ONH. Therefore, ONH strain is a predictor of changes in the stiffness of its micro-environment or changes in the effective force acting in the ONH region. We present computational approaches for estimating ONH elastography measures from optical images of the retina.
Methods :
Confocal microscopy images of a cow lamina cribrosa from an experimental glaucoma study were used (Balasubramanian M, et al, IOVS 2004). Cow eyes obtained fresh were cut equatorially and the posterior segments perfused in oxygenated Dulbecco's solution were positioned in a controlled pressure chamber specifically designed to clamp onto the focusing objective. Images of the lamina cribrosa were acquired 60 minutes after stablizing the chamber pressure at 12 mmHg and 60 minutes after elevating the chamber pressure to 60 mmHg. Deformation field depicting structural changes in the lamina cribrosa was estimated from the successive confocal images using the equations governing patterns of brightness changes or optical flow. Specifically, the governing partial differential equations of optical flow (strong form) was solved using a multiscale finite element method with hierarchical basis functions. Several candidate descriptors of elastography namely a) absolute strain magnitude, b) maximum normal strain, c) maximum shear strain, d) Von Misses coefficient, e) vorticity (as a measure of rigidity), f) divergence (degree of expansion) and g) relative strain ratio were estimated.
Results :
Figure 1 shows planar structural changes in the architecture of the lamina cribrosa estimated non-invasively using our computational approaches. Figure 2 shows elastography of the cow lamina cribrosa under experimental pressure elevations. From the elastography maps, it can be observed that the laminar beams are at elevated strain levels under pressure elevations.
Conclusions :
Computational approaches are useful for non-invasively estimating ONH strain from optical images of the retina (elastography). These elastographic measures are likely to be useful for predicting onset and progression of glaucoma as well as for clinical management of glaucoma using standard optical scans of the retina.
This is a 2021 ARVO Annual Meeting abstract.