In several retinal pathologies, such as AMD and retinitis pigmentosa, function of cones and rods are affected to different extents. To investigate these, an imaging modality is needed that separates the function of both photoreceptor types. Recently, functional imaging of single cones using phase-sensitive OCT has been demonstrated. However, until now, functional imaging of rods was only possible with high resolution systems. Here we differentiate the functional response of rods and cones without resolving single photoreceptors. After stimulation with short illumination in the mesoscopic range, the different temporal dynamics of rods and cones are distinguished by their typical response characteristics.
Computational adaptive optics (CAO) is emerging as an attractive alternative to hardware-based solutions for diffraction-limited optical coherence tomography, e.g., of the human retina. Still, to become a reliable and robust solution, many challenges need to be solved. Here, we present CAO based on multiple randomized sub-apertures in combination with suitable filtering to remove disturbing artifacts. We show that this approach can reliably detect aberrations, and we compare results to other algorithms, such as optimization of imaging quality. We also demonstrate that the filtering of reflecting image structures is essential for a robust determination of aberrations.
Phase-sensitive optical coherence tomography (OCT) is emerging as an imaging modality that detects functional changes in the retina. Besides imaging photoreceptor function, recently, functional changes in the inner plexiform layer (IPL) have been detected using full-field swept-source OCT. The IPL connects neuronal cells which are dedicated for processing different aspects of the visual information, such as edges in the image or temporal changes. A characteristic of signal processing in the IPL is that different aspects of the visual impression are only processed in very specific depths. Here, we present an investigation of these functional signals for different depths in the IPL with the aim to separate different properties of the visual signal processing. Therefore, we investigate the phase changes of three different sub-layers. Whereas the first two depths, closest to the ganglion cell layer, exhibit an increase in the optical path length, the third depth, closest to the bipolar cell layer, exhibits a decrease in the optical path length. Additionally, we found that the second or middle depth is sensitive to temporal changes, showing a maximum increase of the optical path length at a stimulation frequency of around 10 Hz. The results suggest that the responses from different cell types, which are sensitive to different features of the stimulation signal, can be distinguished by phase-sensitive OCT.
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