An adjustable fluid-filled lens or minor
assembly 100 comprising a fluid-filled envelope and a supporting structure therefor; the fluid-filled envelope being constituted by a first wall that is formed of a distensible
elastic membrane 15 having an exterior
optical surface of variable focusing power, a second wall 18 that is spaced from the first wall on a z-axis, and a collapsible
peripheral side wall 17 that extends between the first and second walls, and being filled with a substantially incompressible fluid 16; a membrane holding structure 14 that is attached to a
peripheral edge of membrane 15 for holding the membrane under tension; and one or more selectively operable
actuator assemblies r1, r2, r3 for moving one or more corresponding regions of the
peripheral edge of the membrane on the z-axis towards and away from the second wall 18 for controlling the profile of the peripheral edge of the membrane; wherein the or each
actuator assembly comprises a connecting member 91, 92, 93 that is attached to the membrane or membrane holding structure at a respective actuation point, a
linear actuator 531, 532, 533 that is mounted to the supporting structure and a linkage 81, 82, 83 that is connected between the connecting member and an actuation point a1, a2, a3 on the
linear actuator; wherein the
linear actuator is a linear
SMA actuator comprising an array of SMA wires 53 that are coupled together to work in parallel and which extend transversely of the z-axis, and the linkage is configured for converting
linear motion of the actuation point of the
SMA actuator in a direction transverse the z-axis to
linear motion of the connecting member on the z-axis, thereby to move the corresponding region of the peripheral edge of the membrane 5 towards or away from the second wall 18.