Abstract: A method and assembly for molding plastic optical lenses. The mold assembly comprises an annular retainer ring supporting a pair of generally disc shaped mold parts urged toward each other by a resilient force while separated by one or more gaskets, preferably including at least one soft gasket of uniform thickness between its inside and outside diameters which has the property of softening at elevated temperatures. When the cavity formed between the mold parts and bounded peripherally by the gaskets is filled with a resin formulation in the form of a liquid which then polymerizes when raised to an elevated curing temperature, shrinking and becoming hard and insoluble at room temperature, in the process the softening of the gasket permits the mold parts, under the action of the resilient force, to move towards each other to maintain contact with the formulation as it shrinks and hardens.