An optical measurement device and method are presented for use in non-invasive measurements on a patient's body. The device comprises an illumination assembly configured and operable to generate illuminating light of a predetermined wavelength range; a detection assembly; and a light directing assembly. The detection assembly comprises a first detector unit for detecting a first light signal transmitted through an illuminated body portion and generating first measured data indicative of the detected transmitted light, and a second detector unit for detecting a second light signal reflected from the illuminated body portion and generating second measured data indicative of the detected reflected light. The light directing assembly comprises a light diffuser for scattering back light incident thereto, to thereby direct the illuminating light or the light coming from the body portion back towards the body portion. This technique provides for increasing the amount of light reaching a region of interest inside the body portion and maximizing homogeneity of the first and second detected light signals.