In one aspect, the invention features a method and device for measuring blood concentration of a substance such as glucose in the aqueous humor by illuminating the aqueous humor with a light source at a frequency that is absorbed by the substance to the measured, and then sensing photoacoustically generated sound waves originated within the aqueous humor as a consequence of illumination by the light source. The blood concentration can be estimated from the amplitude of the sound waves received. The method may be combined with other optical techniques for glucose measurement and/or with optical or ultrasonic techniques for topographic mapping of eye structures.