Purchase this article with an account.
Clara Pfäffle, Dierck Hillmann, Hendrik Spahr, Lisa Kutzner, Bastian Kabuth, Sazan Burhan, Felix Hilge, Gereon Hüttmann; Physiologic origin of intrinsic optical signals in human retina. Invest. Ophthalmol. Vis. Sci. 2018;59(9):672.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
After successful detection of intrinsic optical signals (IOS) in the human retina with full-field swept-source optical coherence tomography (FF-SS-OCT), we continued characterizing the signals, in oder to understand their origin and possible value for a better understanding of neuronal path ways in the vision process and diagnosis of deseases.
The IOSs were imaged by FF-SS-OCT, which is able to detect sub-wavelength morphological changes by phase evaluation. The required phase stability is reached by parallel illuminating the field-of-view (FOV) and detecting with a fast area camera (fastcam SA-Z, Photron) at frame rates of up to 75 kHz. The OCT uses wavelengths between 867 nm and 816 nm, which are outside the sensitivity range of the human retina. White light was used to stimulate the retina at specific areas and with a specific time course. Both, OCT and stimulation light, were far below the maximal permissable exposure (MPE), as confirmed by the responsible safety officer. The study was approved by the ethic boards of the University of Lübeck.
During and after the stimulus, we observed an expansion of the optical path length (OPL) of the photoreceptor outer segment (OS). The expansion was limited to the stimulated area and lasted up to seconds after the stimulus had ended. The expansion rate was about 140 nm/s and independent of stimulation intensity or duration.From the time course and characteristics of the IOSs it is conclueded that an osmotic process is likely to cause the measured IOS. Qualitatively, the time course correlates with a concentration change due to neural action potentials, which would also predict a volume change in the ganglion cell layer (GCL). Although obtaining results from the GCL turned out to be difficult since heart-beat induced pulsation disturbed phase measurements, a change of the OPL in the GCL was detected. Compared to the OS, the signal was weaker and laterally shifted by tens of microns (see figure 1).
Osmotic water influx into the extra-cellular matrix seems a reasonable mechanism for the observed IOS. We believe that probing retinal function with FF-SS-OCT will have significant impact, both in research and diagnostics.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Left: phase evaluation of the photoreceptor OS after 5400 ms stimulation Right: averaged phase evaluation of the GCL
This PDF is available to Subscribers Only