Fluorescein, a fluorescent tracer dye, also can leak into the eye. Here is a scan from a patient who received an intravenous injection of fluorescein 1 hour earlier. You can see that some fluorescein has penetrated the retina into the vitreous. This patient has only very mild retinopathy so the leakage is also fairly mild. The Fluorotron comes with a special computer algorithm for subtracting out background and vascular fluorescence so that only penetrated fluorescein is measured.