A probe device for use in non-invasive optical measurements of at least one parameter of the patients blood. The probe device comprises a finger holder in the form of a clip member that secures a fingertip between its clamping legs. The probe device supports a measuring unit for applying optical measurements to a measurement location on the finger and carries a pressurizing assembly operable for applying controllably variable, substantially under-systolic pressure to the finger in the vicinity of the measurement location. Several measurement sessions are performed at the measurement location with at least two different wavelength of incident light to detect light response of the medium and generate measured data indicative thereof, and the pressure applied to the vicinity of the measurement location is simultaneously varied during measurements. The light response of the medium corresponding to different wavelength of the incident light and different pressure values during measurements. The light response of the medium corresponding to different wavelength of the incident light and different pressure values is analyzed, and an optimal pressure value is determined, so as to utilize the corresponding light response of the medium for deriving therefrom the at least on blood parameter.
