Laser Doppler holography of the anterior segment for blood flow imaging, eye tracking, and transparency assessment

Recent updates in choroidal imaging biomarkers

The choroid, a highly vascularized tissue, supplies the outer retina and is responsible for other functions such as thermoregulation, secretion of growth factors, and possibly emmetropization. Choroidal changes, therefore, may play a role in various chorioretinal diseases. The recent surge in publications focusing on the choroid can be attributed to improvements in both resolution and field of view of optical coherence tomography and indocyanine green angiography. Advancements in imaging have transitioned from manual to semi-automated and now fully automated methods for qualitative and quantitative choroidal analysis. These qualitative parameters include choroidal vascular patterns and focal or diffuse changes in the vascular wall, either bulbosity or tortuosity. Quantitative parameters include choroidal thickness, volume, vascularity index, contour, three-dimensional vessel quantification, and blood flow measurements using laser Doppler holography. We discuss these qualitative and quantitative biomarkers in detail, i.e., the underlying principles, clinical use, changes in normal and disease states, and their limitations. This will provide invaluable insights to clinicians in understanding the choroidal changes in physiological and pathological states.

Retinal blood flow reversal quantitatively monitored in out-of-plane vessels with laser Doppler holography

Laser Doppler holography is a planar blood flow imaging technique recently introduced in ophthalmology to image human retinal and choroidal blood flow non-invasively. Here we present a digital method based on the Doppler spectrum asymmetry that reveals the local direction of blood flow with respect to the optical axis in out-of-plane vessels. This directional information is overlaid on standard grayscale blood flow images to depict flow moving towards the camera in red and flow moving away from the camera in blue, as in ultrasound color Doppler imaging. We show that thanks to the strong contribution of backscattering to the Doppler spectrum in out-of-plane vessels, the local axial direction of blood flow can be revealed with a high temporal resolution, which enables us to evidence pathological blood flow reversals. We also demonstrate the use of optical Doppler spectrograms to quantitatively monitor retinal blood flow reversals.