Variable focus optical devices, in particular lenses, can include a cavity at least partially defined by a flexible member (2), which may be retained between engaging portions of a frame member (8) and a ring member (12), such that a peripheral region of the membrane is caused to change direction more than twice. The engaging portions of the ring and frame may be high-friction surfaces. In addition, methods of filling a cavity of a lens with transparent fluid, methods of adjusting the pressure of fluid in the cavity, and methods of sealing such a cavity are described, as well the use of such lenses in adjustable spectacles.