A method for monitoring bladder function in an animal having a bladder, the method including positioning of a light emitter and a light detector on the animal's skin adjacent to the animal's bladder, emitting light at the bladder with the emitter while detecting light with the detector, and collecting data representative of detected light during bladder activity, to provide an indication of bladder function. Also provided are light shield apparatus and filter apparatus for near infrared spectroscopy (NIRS) bladder monitoring.