  Laser Doppler holography (LDH) is a full-field interferometric imaging
technique recently applied in ophthalmology to measure blood flow, a parameter
of high clinical interest. From the temporal fluctuations of digital holograms
acquired at ultrafast frame rates, LDH reveals retinal and choroidal blood flow
with a few milliseconds of temporal resolution. However LDH experiences
difficulties to detect slower blood flow as it requires to work with low
Doppler frequency shifts which are corrupted by eye motion. We here demonstrate
the use of a spatio-temporal decomposition adapted from Doppler ultrasound that
provides a basis appropriate to the discrimination of blood flow from eye
motion. A singular value decomposition (SVD) can be used as a simple, robust,
and efficient way to separate the Doppler fluctuations of blood flow from those
of strong spatial coherence such as eye motion. We show that the SVD
outperforms the conventional Fourier based filter to reveal slower blood flow,
and dramatically improves the ability of LDH to reveal vessels of smaller size
or with a pathologically reduced blood flow.
