Lens mould

A cast mould for use in the manufacture of a contact lens by the polymerisation of a flowable precursor comprises a female mould part (2) and a male mould part (4). The female mould part (2) has a concave first surface region (10) adapted to receive the flowable precursor in use, and a second surface region (12c, 14a). The male mould part (4) has a convex first surface region (22) and a second surface region (24a, 24b, 24c). The male mould part (4) is engageable with the female mould part (2) to define a lens-forming recess (30) between the concave and convex surface regions (10, 22) and to define a first overflow cavity (32) between said second surface regions (12c, 14a; 24a, 24b, 24c). The first overflow cavity (32) is adapted to receive excess flowable precursor displaced from the lens-forming recess (30) in use, and the first overflow cavity (32) is provided with first retaining means such that, in use, after polymerisation, polymer in the first overflow cavity (32) is mechanically interlocked with a single one of the mould parts (2, 4) after separation of the mould parts (2, 4).