We report on laser Doppler perfusion imaging of human retinas using digital holography with near infrared light. The optical signal is obtained by exploiting the Doppler frequency shifts of cross-polarized light. A polarization beam splitter is used to illuminate the retina with a given linear polarization and collect cross-polarized light. The interference pattern is sampled using two detection channels: a 40 Hz sCMOS camera for real-time monitoring, and a 39 kHz CMOS camera to properly sample the Doppler broadened spectrum of the light backscattered by the retina. The holograms are numerically reconstructed by angular spectrum propagation and then processed on sliding windows of 512 images. For each short-time window, the Fourier transformation along the temporal dimension is computed, and the Doppler signal is drawn from the first moment of the high-pass filtered Fourier transformation. In the resulting images, the contrast is derived from the tissue perfusion which is related to both the local speed and concentration of blood cells. The cardiac cycle of retinal vessels is apparent, and choroidal vasculature can also be observed. Further analysis of the vessels frequency signature allowed for the discrimination of retinal and choroidal vessels. The blood flow is sampled with a temporal resolution of 13 ms while the spatial resolution is estimated to be 20 µm and the field of view approximately 2*2 mm.
Leo Puyo, Mathias Fink, Michel Paques, and Michael Atlan, "Laser Doppler perfusion imaging of human retina using digital holography (Conference Presentation)," Proc. SPIE 10474, Ophthalmic Technologies XXVIII, 1047405 (Presented at SPIE BiOS: January 27, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2289484.5751477430001.
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