The actuator (see FIG. 2) comprises a barrel 16 and a plunger 22 received within the barrel. A clutch mechanism 54 is operable between the plunger and the barrel. In the engaged condition of the clutch, the plunger is advanced by rotation relative to the barrel. An axial load on the plunger disengages the clutch mechanism, allowing the plunger to be advanced axially whilst rotating the driven member 60. Two-handed or one-handed operation is therefore possible. A freely rotatable collar 27 on the plunger allows the plunger to be returned to its retracted position with a linear rearward movement whilst allowing rotation of the plunger. A resilient ring 35 mounted in a cross-passage 32 in a bush 28 at the forward end of the plunger provides a measured degree of frictional resistance to the plunger returning under its own weight to the retracted position. The ring may be replaced by a C-shaped resilient element (see FIG. 13). The actuator can be used in combination with a lens delivery device (see FIGS. 1 and 2).
