holes are arranged around the periphery of the central raised area 43 so that they are not on the line joining the ribs 36 and 37 but are offset from that line the upper surface of the raised portion 43 is part spherical having a radius of curvature substantially equal to that of the convex surface of the lens the edge 41 has a diameter approximately equal to or slightly less than the outer diameter of a lens one of which is indicated in fig3 and 4 at 47 the axial position of the edge 41 is such that it is slightly spaced from the lens 47 when the curved upper surface of the raised portion 43 first contacts the center portion of the lens with the membrane flat in the position shown in fig3 in operation the uppermost compartment defined by the wall 23 is unscrewed from the first lens storing portion 11 so as to expose the compartment within which the first lens is stored upon the base 12 the lens thus is exposed upwardly with its convex surface uppermost the head 24 is at this stage stored within the storage liquid in the compartment 22 the portion 27 is then unscrewed from the compartment 22 so the head 24 can be removed from the liquid prior to removal the bulb 26 can be depressed and released to draw some of the liquid into the head upstream of the membrane 42 thus the membrane is effectively surrounded by liquid and is fully wetted by same the bulb is then slightly depressed and the head brought up to the.