Abstract: A contact lens cleaning and disinfecting apparatus with a cavity (14) in which a contact lens is to be cleaned by an aqueous non-chemosterilant liquid such as a saline solution. An ultra-sonic transducer (20) applies vibrations to the cavity (14). The oscillator driving the transducer includes a transformer feedback circuit using one or more cores of high magnetic permeability and low core loss to give a stable resonant frequency. A timer (34) may be driven from this resonant frequency. In one embodiment the cavity (14) and the sealing cap (16) may be removable together with the transducer (20) from the rest of the housing of the apparatus so that lenses can be transported conveniently after cleaning and before use. According to another embodiment the waste heat from power transistors (Q2, Q3) can be used to heat the cleaning liquid in the cavity.