The present invention relates to devices, systems and methods for determination or selection of a lens power based on the postoperative vitreous length of an eye. The wound dressing includes an impermeable backing material and a sealing member to provide a seal against the skin. The cassette and the sensors may be so configured and positioned that a suitable end effector may move sheets of material between storage locations in the cassette and test locations adjacent the sensors. Whether the user is authorized and has sufficient credit are then verified. , and a foaming step during which air is added to said preheated milk such as to produce milk foam.