Off-axis optical coherence tomography imaging of the crystalline lens to reconstruct the gradient refractive index using optical methods

13 pags., 7 figs.
Earlier studies have shown that the gradient index of refraction (GRIN) of the crystalline lens can be reconstructed in vitro using Optical Coherence Tomography (OCT) images. However, the methodology cannot be extended in vivo because it requires accurate measurements of the external geometry of the lens. Specifically, the posterior surface is measured by flipping the lens so that the posterior lens surface faces the OCT beam, a method that cannot be implemented in vivo. When the posterior surface is imaged through the lens in its natural position, it appears distorted by the unknown GRIN. In this study, we demonstrate a method to reconstruct both the GRIN and the posterior surface shape without the need to flip the lens by applying optimization routines using both on-axis and off-axis OCT images of cynomolgous monkey crystalline lenses, obtained by rotating the OCT delivery probe from -45 to +45 degrees in 5 degree steps. We found that the GRIN profile parameters can be reconstructed with precisions up to 0.009, 0.004, 1.7 and 1.1 (nucleus and surface refractive indices, and axial and meridional power law, respectively), the radius of curvature within 0.089 mm and the conic constant within 0.3. While the method was applied on isolated crystalline lenses, it paves the way to in vivo lens GRIN and posterior lens surface reconstruction.
European Research Council (ERC) under European Union’s Horizon 2020 research and innovation programme (H2020-MSCA COFUND-2015 FP-713694, MULTIPLY); Spanish government (FIS2014-56643-R, FIS2017-84753-R); European Research Council under the European Union’s Seventh Framework programme (ERC-2011-AdG-2940); National Eye Institute (R01EY021834; F31EY021444); Ruth L. Kirschstein National Research Service Award Individual Pre-doctoral Fellowship (P30EY14801 Center Core Grant); the Florida Lions Eye Bank and Beauty of Sight Foundation; the Henri and Flore Lesieur Foundation.