Zinc protoporphyrin (ZPP) is a fluorescent compound that accumulates in red blood cells and is used as a biomarker for nutritional iron deficiency. To determine a place in tissue where ZPP fluorescence can be measured directly, we estimated the ZPP fluorescence compared with background fluorophores in oral mucosa (i.e. collagen and FAD) and the retina.
ZPP fluorescence is 4 to 6 orders of magnitude lower than background fluorescence in oral mucosa, but is comparable to background in the retina. Therefore, we developed a computational model of the eye, using parameters that were identified either by literature search, or by direct experimental measurement.
By incorporating fluorescence into Steven Jacques’ original code for multi-layered tissue, we performed Monte Carlo simulation of fluorescence in the retina and determined that if the beam is not focused on a blood vessel in a neural retina layer or if part of light is hitting a small vessel, ZPP fluorescence will be 10-20 times higher than background lipofuscin fluorescence coming from the retinal pigment epithelium (RPE) layer directly below.