Abstract
Purpose :
Fluorescein angiography has been the workhorse diagnostic technique for investigating abnormalities in the retinal circulation for 50 years, however there are associated risks of nausea or even death associated with reaction to fluorescein dye. We report an alternative using a hypoxic intervention and multispectral imaging to exploit the oxygen-dependent spectral absorption of haemoglobin to instead use blood-oxygen saturation as the contrast agent.
Methods :
Experimental apparatus consisted of a commercial fundus camera (Topcon 50DX) coupled to an Image Replicating Imaging Spectrometer for snapshot multispectral imaging in 8 spectral bands. Healthy subjects inhaled a hypoxic air mixture (5% O2, 95% N2), inducing a wave of deoxygenated blood, which, when reaching the retina acts as the contrast agent to enable angiography. Computer processing of the multispectral images allows the extraction of an angiographic sequence.
Results :
Using the multi-spectral image sequences we generated an oximetric-contrast image sequence, which closely resembles a typical fluorescein angiogram, showing comparable features such as the characteristic sequential vessel filling (as seen in figure 1), and laminar flow in branching veins.
Conclusions :
We have demonstrated the use of an acute hypoxic intervention during multispectral imaging of the retina to generate dye-free angiographic sequences for the first time. This technique has promise for clinical assessment of retinal circulation and is a unique alternative to the fluorescein angiogram that is both non-invasive and avoids the negative effects of the use of fluorescein. Furthermore, unlike fluorescein, the technique can be repeated after intervals as short as about one minute.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.