Photobiomodulation (PBM) is a modulation of monochromatic light or laser irradiation (LI) on biosystems. It is reviewed from the viewpoint of extraocular phototransduction in this paper. It was found that LI can induce extraocular phototransduction, and there may be an exact correspondence relationship of LI at different wavelengths and in different dose zones, and cellular signal transduction pathways. The signal transduction pathways can be classified into two types so that the Gs protein-mediated pathways belong to pathway 1, and the other pathways such as protein kinase Cs-mediated pathways and mitogen-activated protein kinase-mediated pathways belong to pathway 2. Almost all the present pathways found to mediate PBM belong to pathway 2, but there should be a pathway 1-mediated PBM. The previous studies were rather preliminary, and therefore further work should be done.