Non-invasive measurement techniques for quantitative assessment of optic nerve head blood flow

Abstract

Diseases of the optic nerve head involving changes in blood flow are common. However, the pathophysiology is not always fully understood. Several non-invasive methods for measuring optic nerve head blood flow are available, but currently no gold standard has been established. Methods for measuring blood flow in optic neuropathies including colour Doppler imaging, retinal function imager, optical coherence tomography angiography and laser speckle flowgraphy are reviewed. Ultrasound colour Doppler imaging is a fast measurement technique where several different parameters, especially the blood flow velocity, can be calculated. Though used for many years in ophthalmology, its use is not standardized and it requires significant observer skills. The retinal function imager is a direct method where the haemoglobin in erythrocytes is visualized and blood flow velocities in retinal vessels are calculated from a series of photos. The technique is not suitable for direct measurement of blood flow within the optic nerve head. Laser speckle flowgraphy uses a laser light which creates a light scatter pattern in the tissue. Particles moving in the area causes changes in the speckle pattern from which a relative blood flow can be estimated. It is, however, not known whether optic nerve head microcirculation is measurable with the technique. Optical coherence tomography angiography uses multiple scans to evaluate blood flow with good reproducibility but often problems with artefacts. The technique is continuously being refined and increasingly used in research as a tool for the study of blood flow in retinopathies and optic neuropathies. Most of the conducted studies are based on small sample sizes, but some of the methods show promising results in an optic nerve head blood flow research setting. Further and larger studies are required to provide standardized and comparable measurements before one or more of the methods can be considered clinical helpful in daily practice.

Microcirculatory model predicts blood flow and autoregulation range in the human retina: in vivo investigation with laser speckle flowgraphy

“…In addition, it is often an indicator of cardiovascular or cerebrovascular disease (16a, 45). To date, there is only partial understanding of the regulation of blood supply in the retina and the optic nerve head (ONH), partially due to the lack of a gold-standard, noninvasive way to quantify blood flow (BF) (136).…”

Assessment of optic nerve vascularity in healthy eyes using superb microvascular imaging: a preliminary study

“…Imaging methods including retinal function imager (RFI), optical coherence tomography angiography (OCTA), laser speckle flowgraphy (LSFG), and Doppler US (CDUS/PDUS) may be used for measuring optic nerve blood flow (5). The RFI is a direct method in which the hemoglobin in erythrocytes is visualized and blood flow velocities are calculated from a series of photos.…”

“…The RFI is a direct method in which the hemoglobin in erythrocytes is visualized and blood flow velocities are calculated from a series of photos. It is highly suitable for research and clinical trials, but it is too time-consuming to integrate in daily practice (5,11,12). The OCTA is a technique wherein images are obtained using a swept source.…”

Ultrasonographic tissue perfusion analysis at implant and palatal donor sites following soft tissue augmentation: A clinical pilot study

“…FMBV evaluation requires an offline image analysis technique applied to raw exported three‐dimensional (3D) power Doppler US (Stevenson et al, 2015; Welsh et al, 2019). This method has been used to assess blood flow and perfusion of the kidney (Welsh et al, 2019), optic nerve (Vosborg et al, 2020), placenta (Lai et al, 2010) and foetal organs (Hernandez‐Andrade, Thuring‐Jonsson, et al, 2004; Hernandez‐Andrade et al, 2007), among others.…”