Full-Field Optical Coherence Tomography (FF-OCT) reveals submicrometric morphological details in retinal explants without the use of contrast agents. Notably, in the nerve fiber and ganglion cell layers, FF-OCT images reveal nerve fibers bundles, single axons, capillaries and even some ganglion cell bodies.
Dynamic FF-OCT (D-FF-OCT) takes advantage of the temporal evolution of the local FF-OCT signal to reveal a movement-dependent contrast inside tissues. Notably, the D-FF-OCT signal depends on cellular motility and membrane fluctuations. Compared to regular FF-OCT images, the signal from stationary structures such as nerve fibers is reduced, and contrast inside cells is enhanced, revealing many more cells, as well as the position of nuclei, and cell metabolism.
We used a multimodal D-FF-OCT and fluorescence microscope to compare and identify the structures observed in both FF-OCT and D-FF-OCT.
In the ganglion cell and inner nuclear layers in both macaque and mouse, two different cell sizes could be measured, which correlated well with ganglion and amacrine cell diameters found in the literature for these two species. We could also detect cell bodies of the photoreceptors in the outer nuclear layer. To our knowledge, this is the first time that an OCT technique can reveal these cell bodies.
Finally, to investigate post-mortem tissue changes, time series were acquired over periods of 24 hours and cell contrast was plotted in time to monitor the decrease in intracellular activity over time.
It is anticipated that dynamic FF-OCT may be used to non-invasively monitor viability and functional changes in the retina.