Abstract: The present invention relates to a portable illuminating device (110) comprising at least one illuminating light source (112) emitting light of a wavelength comprised in the range of 450 to 495 nm, preferably, comprising at least one further illuminating light source (112) emitting light of a wavelength comprised in the range of 620 nm to 750 nm; a diffuser (113) scattering the light of said illuminating light source (112) at least in part in the direction of at least one eye, preferably at least one cornea and/or retina, of said subject; and a mounting mechanism (114) for fixing the portable illuminating device (110) to the body of a subject. Preferably, said diffuser (113) scatters the light of said illuminating light source (112) at least in part in the direction of at least one eye and in the direction of at least a part of the facial skin of a subject.