One of the leading causes of blindness in the Western world are vascular diseases affecting the retina. The arteries and veins inside the light-sensitive layer in the back of the eye – the retinal vasculature – are an intricate network supplying the inner retina with crucial nutrients while removing metabolic waste.  The heterogeneity in space and time of blood flow in this microvasculature is critical as the retina has one of the highest metabolic demands of the central nervous system.

Pathological retinal neovascularisation and oedema – that is swelling, thickening, or unusual growth in the retinal vasculature – are commonly responsible for certified visual loss.  Therefore, understanding the spatial and temporal heterogeneity and active regulation of retinal blood flow in the retina is critical for the diagnosis of retinal vascular disease. Furthermore, these blood vessels are affected by systemic vascular diseases and, as such, evidence of these conditions may be observed through the microvasculature inside the eye.

Recently, a technique known as optical coherence tomography angiography (OCTA) has been developed as a non-invasive approach to visualising blood vessels. This method uses the reflectance of light on the surface of moving blood vessels to map the vasculature of the retina.

A multi-disciplinary team, headed by Prof Dao-Yi Yu at the Lions Eye Institute (affiliated with the UWA Centre for Ophthalmology and Visual Science) are using OCTA to reveal remarkable spatial and temporal heterogeneity of retinal capillary perfusion. The project aims to use OCTA as a non-invasive tool for the early detection of retinal vascular diseases.

NIF Informatics Fellow, Dr Andrew Mehnert, is contributing his analysis expertise to guide improvements in OCTA instrumentation and algorithms. Image analyses, undertaken in the Characterisation Virtual Laboratory (CVL) using both MATLAB and FIJI/ImageJ, showed remarkable resolution of capillary perfusion in the macular region of human and porcine subjects.

Left: En face mean intensity projection through 31 OCTA images from the macular region of a human subject. Right: Coefficient of variation along vessel centrelines showing spatial and temporal heterogeneity of capillary perfusion. The colour bar indicates the variation from dark blue (no variation) through to red (most variation).

The developed software tools have been used for characterising spatio-temporal variation of capillary perfusion in OCTA images.

Experimental results to date are both valuable and encouraging because they may be potentially useful for clinical diagnostic purposes and can be used to guide improvements in OCTA instruments and new algorithm development. These results move towards a non-invasive tool for the early detection of retinal vascular diseases in humans, and may also be used for other investigations of capillary perfusion where the retina is an appropriate model for microcirculation studies.

For further information, please contact Dr Andrew Mehnert.

This story was contributed by the University of Western Australia.

Researchers at the Australian Research Council Centre of Excellence for Coral Reef Studies, the University of Western Australia, Curtin University, Aix-Marseille University in France, and the US National Oceanic and Atmospheric Administration wanted to know the history of coral bleaching events on the Great Barrier Reef and how corals are responding to climate change.

Hard long-lived corals, such as Porites, are the backbone of reef ecosystems such as the Great Barrier Reef. Such reef-building corals are sensitive to light levels and temperature. Reef-building corals are already reaching their limits with every heatwave. With ocean temperatures rising, can they hope to survive more frequent extreme temperature events?

Dr. Thomas DeCarlo drilling a 2+ meter core from a massive coral on the Great Barrier Reef

The team of researchers collected Porite core samples across the northern Great Barrier Reef, the Coral Sea, and New Caledonia, bring them to the WA NIF Node at the University of Western Australia, where they were scanned on the Bruker Skyscan 1176 in vivo micro-CT. 3-dimensional image stacks of density variations revealed ‘bands’ within the coral skeletons, corresponding to age. Also seen were high/low density ‘stress bands’, corresponding to environmental stressors such as exceptionally high water temperature.

μCT scans (dark/light shading = low/high density) reveal high-density stress bands and partial mortality scars preserved within the skeletons of long-lived Porites corals.

Some of the oldest (and longest) core samples had over 200 annual bands, meaning they were a living coral that has been growing for two centuries. By comparing stress bands to age, change-induced bleaching episodes were mapped, providing a timeline of coral bleaching events. Three striking observations followed: First, the researchers found the first piece of evidence that coral bleaching has occurred prior to the 1980s. Second, a significant increase in the frequency of stress bands was seen over time, consistent with the effects of global warming sparking more frequent coral bleaching events. Finally, recent (within the past few years) acclimatization was seen, whereby corals became less sensitive to heat stress follow repeated exposure to marine heatwaves. These results, published in early 2019, offer hope that reef-building corals surviving heatwaves may be able to adapt for future heatwaves.

This story was contributed by the University of Western Australia. For enquiries, please contact Ms Diana Patalwala.