Fluorescence

Fluorescein angiography is an application of the physical phenomenon of fluorescence.1 Fluorescence is a type of photoluminescence that occurs when susceptible molecules known as fluorophores absorb electromagnetic energy, temporarily exciting them to a higher energy state. As the molecules return to their original energy level, they emit light of a different, usually longer wavelength. Unlike phosphorescence, which continues to occur after the excitation source is removed, fluorescence requires continuous excitation. Once the excitation source is removed, emission of fluorescence stops almost immediately

Fluorescence occurs naturally in certain compounds and may occasionally be observed in the human eye. Optic nerve drusen, astrocytic hamartomas, lipofuscin pigments in the retina, and the aging human lens are all believed to exhibit natural fluorescence that can be documented with photographic techniques.

Indications and Uses

The most common uses of fluorescein angiography are in retinal or choroidal vascular diseases such as diabetic retinopathy, age-related macular degeneration, hypertensive retinopathy and vascular occlusions. Typically, these are clinical diagnoses and the angiogram is used to determine the extent of damage, to develop a treatment plan or to monitor the results of treatment. In diabetic retinopathy the angiogram is useful in identifying the extent of ischemia, the location of microaneurysms, the presence of neovascularization and the extent of macular edema. In age-related macular degeneration, angiography is useful in identifying the presence, location and characteristic features of choroidal neovascularization for possible treatment with laser photocoagulation, photodynamic therapy, or antiangiogenic medications.