Retinal blood flow in critical illness and systemic disease: a review

Abstract

Background: Assessment and maintenance of end-organ perfusion are key to resuscitation in critical illness, although there are limited direct methods or proxy measures to assess cerebral perfusion. Novel non-invasive methods of monitoring microcirculation in critically ill patients offer the potential for real-time updates to improve patient outcomes.

Main body: Parallel mechanisms autoregulate retinal and cerebral microcirculation to maintain blood flow to meet metabolic demands across a range of perfusion pressures. Cerebral blood flow (CBF) is reduced and autoregulation impaired in sepsis, but current methods to image CBF do not reproducibly assess the microcirculation. Peripheral microcirculatory blood flow may be imaged in sublingual and conjunctival mucosa and is impaired in sepsis. Retinal microcirculation can be directly imaged by optical coherence tomography angiography (OCTA) during perfusion-deficit states such as sepsis, and other systemic haemodynamic disturbances such as acute coronary syndrome, and systemic inflammatory conditions such as inflammatory bowel disease.

Conclusion: Monitoring microcirculatory flow offers the potential to enhance monitoring in the care of critically ill patients, and imaging retinal blood flow during critical illness offers a potential biomarker for cerebral microcirculatory perfusion.

Keywords: Critical illness; Optical coherence tomography angiography; Retinal blood flow.

Fig. 1

Optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) of the retina. a En face fundus image showing the optic disc and the macula. b OCT image showing the retinal layers in cross-section passing through the fovea centralis at the location indicated by the bold central arrow in (a). The vitreous (inside of the eye) is at the top of the image and the choroid capillary network (choriocapillaris) is at the bottom. The retinal nerve fibre layer (RNFL) is outlined in red, the inner nuclear layer in blue and the photoreceptor nuclei in yellow, using the manufacturer’s segmentation algorithm. c En face OCTA image of the superficial vascular plexus (SVP) at the level of the retinal ganglion cell nuclei (retinal level indicated by the tip of the connecting arrow). d En face OCTA image of the intermediate capillary plexus (ICP) at the inner border of the inner nuclear layer (retinal level indicated by the connecting arrow tip). e En face OCTA image of the deep capillary plexus (DCP) at the outer border of the inner nuclear layer (retinal level indicated by the connecting arrow tip). f En face OCTA image of the choriocapillaris (retinal level indicated by the connecting arrow tip)