Interpretation of fluorescein angiogram is based upon the two most important features: the blood retinal barrier and the barrier between the choroid and retinal pigment epithelium (RPE). Blocking of fluorescence cre­ates hypofluorescence, whereas excessive fluoresc­ence produces hyperfluorescence. Occlusion of the blood vessel irrespective of its anatomical position shows a filling defect. Extravasation of dye, either impregnates into the tissue or fills a space containing exudates or transudate. The first phenomenon is known as staining and the second pooling, or leakage. Certain substances like drusen of the disc and the lens possess special property of fluorescence even without any fluorescein in the circulation is known as autofluorescence.