Contact lens mold

A polyolefin mould for casting contact lenses from a polymerisable monomer composition which shrinks on polymerization, said mould comprising:

• (a) male and female mould halves each of which has a diaphragm portion which is shaped to provide a surface corresponding to a lenticular surface, said mould halves, when closed together, cooperating to define a mould cavity for receiving a volume of said monomer composition;
• (b) at least one of said mould halves having a non-flexible shoulder portion surrounding said cavity and shaped so that on closing the mould under a closing pressure said shoulder portion engages with said other mould half in an essentially line contact and forms a light-tight seal of said cavity;
• and, (c) the diaphragm of at least one of said mould halves being sufficiently flexible to be deflected into said cavity under forces exerted on said mould by said monomer composition when polymerized in said closed cavity without distorting peripheral portions of the mould in the region of said shoulder, the male and female mould halves are each provided with a non-flexible shoulder portion, the angle which each shoulder makes with the axis of the mould differing slightly so that on closing the mould the shoulder portions meet in substantially line contact.