Contact lenses are made in a number of ways. Soft lenses are most often cast-molded – with this process, the polymer material that the lens is made out of is inserted (in liquid state) into a two-piece mold. Next, the two pieces are pressed together to set and form the lens diameter, curvature, power, and edge. Finally, the contacts are then allowed to cure, which brings them to a solid state, while still remaining soft and pliable. They are then stored in sterile solution that mimics human tears, and then they are wrapped in a plastic pack, and shipped out.
Soft lenses can also be cut in a solid state, and then hydrated afterwards. And a third technique is called spin-casting. In this process the polymer is spun into the needed shape and prescription, and then allowed to firm into a pliable, soft lens. When the process is complete, all soft lenses are composed 30% to 50% water.
Gas-permeable lenses are made a bit differently. First, the liquid lens material is solidified into rods, which are then cut down into buttons. Then the buttons are cut into finished lenses using a computer-lathe. This computer-aided process creates a gas-permeable lens that is custom-fitted to the exact curvature of the patient’s eyes.