A system for use in monitoring one or more conditions of a subject's body, the system comprising a control unit comprising: an input port for receiving defocused image data measured by a pixel detector array and being in the form of a sequence of speckle patterns generated by a portion of the subject's body in response to illumination thereof by coherent light according to a certain sampling time pattern; a memory utility for storing one or more predetermined models, the model comprising data indicative of a relation between one or more measurable parameters and one or more conditions of the subject's body; and a processor utility configured to: process the defocused image data and determining a spatial correlation function between successive speckle patterns in the sequence, and determining a time varying spatial correlation function in the form of a time-varying function of the position of the peak of the spatial correlation function, the time-varying spatial correlation function being indicative of a change of the speckle pattern over time; select at least one parameter of the time-varying spatial correlation function, and apply to said at least one parameter one or more of the models to determine one or more corresponding body conditions; generate output data indicative of said one or more corresponding body conditions; characterized in that the said one or more body conditions to be determined is from the following list of conditions: blood glucose concentration, blood alcohol concentration, intra-ocular pressure. an input port for receiving defocused image data measured by a pixel detector array and being in the form of a sequence of speckle patterns generated by a portion of the subject's body in response to illumination thereof by coherent light according to a certain sampling time pattern; a memory utility for storing one or more predetermined models, the model comprising data indicative of a relation between one or more measurable parameters and one or more conditions of the subject's body; and a processor utility configured to: process the defocused image data and determining a spatial correlation function between successive speckle patterns in the sequence, and determining a time varying spatial correlation function in the form of a time-varying function of the position of the peak of the spatial correlation function, the time-varying spatial correlation function being indicative of a change of the speckle pattern over time; select at least one parameter of the time-varying spatial correlation function, and apply to said at least one parameter one or more of the models process the defocused image data and determining a spatial correlation function between successive speckle patterns in the sequence, and determining a time varying spatial correlation function in the form of a time-varying function of the position of the peak of the spatial correlation function, the time-varying spatial correlation function being indicative of a change of the speckle pattern over time; select at least one parameter of the time-varying spatial correlation function, and apply to said at least one parameter one or more of the models to determine one or more corresponding body conditions; generate output data indicative of said one or more corresponding body conditions;