Contact lens buttons, 5 of 5

Two colourless buttons from which contact lenses are made. The buttons, manufactured by Contamac, are supplied to specialist lens manufacturers who lathe them to exacly fit the eye. The buttons are made from a mixture of around 10 liquid monomers which add a range of properties such as oxygen permeability, stability, tints etc. This mixture is poured into moulds and polymerised, using heat in this instance, turning the liquid into a hard polymer. The hardened material is removed from the mould and annealed, a heating process which allows the moulded material to relax and lose stresses created from being trapped inside the moulded rod. This annealing process also drives the polymerisation to completion. The rods are then sliced into buttons from which contact lenses are eventually made. Coloured handling tints enable users to see the lenses more readily and distinguish left from right lenses.

AIBDC : 008096.5