Nonvisual Photosensitivity and Circadian Vision

Our belief about visual system as functional tool providing only image formation, and in a common senseaninterpretativedepictionofthesurroundingrealworld,hasbeendrasticallychangedbyrecent (andoldbutrevised)achievementsonnonimage-formingvision,morewidelytermedasnonvisualphotoreceptionornonvisualphotosensitivity(NVPforboth).Classicalstudiesininvertebrateandlower vertebratespecieshavedescribed,namely,attime,extraocularorextraretinalphotosensitivecells whichexertedanancillaryroletoobviouseye-likestructuresinmeredetectionofenvironmentalirradiance(oneforalltheso-calledthirdeye,i.e.,thepinealgland,oflowervertebrateorganisms).Suchrole assumesremarkableimportanceinthoseanimalsthatlackobviouseyesorwithpooropticalapparatus.