Light Targeted Angiography (LTA)
Light-Targeted Angiography was initially developed to provide a better means to study retinal vasculature and blood flow. It consists of encapsulating a fluorescent dye, such as carboxyfluorescein, a derivative of the more commonly used fluorescein dye, in heat-labile liposomes. The concentration of dye in the liposomes is sufficiently high to cause fluorescence quenching, thus making the circulating intact liposomes invisible in a typical angiogram.
As seen in the video clip of a rat fundus, LTA shows retention of dye in the small blood vessels of the eye (choroidal neovascular (CNV) bed) and not in the normal vasculature. When the dye is released from the liposome by application of gentle heat, it is diluted in the plasma and yields a bright fluorescent bolus that selectively highlights either retinal or choroidal vessels as the blood flow carries away the bolus. By following the progression of this bolus from the arteries through the arterioles, capillaries, and venules, selective high-quality angiograms of the retinal vasculature and the choriocapillaris have been generated in both normal animals and animals which serve as models for AMD and other diseases.
Light Targeted Angiogram BEFORE Light Targeted Occlusion. See LTO for AFTER Image.
These light-targeted angiograms yield images at a quality unsurpassed by conventional angiography and provide quantitative hemodynamic information. RetinaPharma believes that LTA will be capable of visualizing vessels in both classic and occult forms of AMD.
In Detail
Benefits of LTA
The historic lack of effective treatments for AMD has made detailed diagnostic imaging of the retina relatively unnecessary. In a small subset of wet-AMD cases, angiography shows that the offending new blood vessels are outside of the central foveal region, and thus suitable targets for highly-damaging laser photocoagulation. Otherwise there has been little need to generate more precise images. The arrival of newer treatments such as photodynamic therapy makes improved imaging of significant value to physicians.
Light-Targeted Angiography offers a number of advantages over the current standard that uses systemic sodium fluorescein and includes the following:
- Enhanced visualization of selected vasculature without interference from the fluorescence of neighboring vessels (even underlying or overlying vascular beds) or tissues owing to leakage of dye.
- Identification of neovasculature structures and location of their feeder vessels.
- Better classification of patients than current "classic" and "occult" designations.
- Ability to perform repeated angiograms owing to rapid clearance of dye after each release.
- Ability to perform angiograms in both eyes in one visit owing to a sufficiently long therapeutic window.