Abstract
PurposeWe describe a novel approach to analyze fluorescein angiography to investigate fluorescein flow dynamics in the rat posterior retina as well as identify abnormal areas following laser photocoagulation.MethodsExperiments were undertaken in adult Long Evans rats. Using a rodent retinal camera, videos were acquired at 30 frames per second for 30 seconds following intravenous introduction of sodium fluorescein in a group of control animals (n = 14). Videos were image registered and analyzed using principle components analysis across all pixels in the field. This returns fluorescence intensity profiles from which, the half-rise (time to 50% brightness), half-fall (time for 50% decay) back to an offset (plateau level of fluorescence). We applied this analysis to video fluorescein angiography data collected 30 minutes following laser photocoagulation in a separate group of rats (n = 7).ResultsPixel-by-pixel analysis of video angiography clearly delineates differences in the temporal profiles of arteries, veins and capillaries in the posterior retina. We find no difference in half-rise, half-fall or offset amongst the four quadrants (inferior, nasal, superior, temporal). We also found little difference with eccentricity. By expressing the parameters at each pixel as a function of the number of standard deviation from the average of the entire field, we could clearly identify the spatial extent of the laser injury.ConclusionsThis simple registration and analysis provides a way to monitor the size of vascular injury, to highlight areas of subtle vascular leakage and to quantify vascular dynamics not possible using current fluorescein angiography approaches. This can be applied in both laboratory and clinical settings for in vivo dynamic fluorescent imaging of vasculature.
Highlights
The retina is the only place in the body that allows non-invasive, direct in vivo visualization of neuronal tissue and vasculature
Dynamic fluorescein angiography Compared to en face fundus images taken under broadspectrum light (Figure 1A), the presence of fluorescein acts as a contrast medium that improves the resolution of both major and minor retinal vessels (Figure 1B)
When fluorescein angiography is repeated 30 minutes apart, we find that half-rise (Arteries 0.0260.03 s; veins 0.360.2 s, capillaries/choroid 0.260.2 s) and half-fall (Arteries 1.160.6 s; veins 0.760.4 s, capillaries/choroid 0.960.5 s), in the inferior quadrant inner eccentricity zone show very little difference
Summary
The retina is the only place in the body that allows non-invasive, direct in vivo visualization of neuronal tissue and vasculature. Since the early 1900s intravenous injection of sodium fluorescein has been shown to temporarily highlight retinal vessels [3,4], improving in vivo assessment of the retinal circulation and blood-retinal-barrier integrity [5,6,7]. It has since been adopted as a clinical tool for a host of conditions including glaucoma, diabetes, vascular occlusion, neovascularization and inflammatory disease [4,8,9,10]. Pre-clinically, fluorescein angiography has been utilized in studies of vascular disease, angiogenesis and blood-neural-barrier compromise [13,14,15,16]
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