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I’ve heard that heat may crack/craze AR lenses when adjusting glasses in the bead pan or hot air warmer. How can I avoid this happening?

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Anti-reflective lenses should not be exposed to extreme temperatures, such as those found in most frame adjustment devices, which may reach temperatures over 150F. Lens substrates such as CR-39, polycarbonate and high-index are more susceptible to heat expansion than the materials found in anti-reflective surfaces. As a result, when AR lenses are exposed to extreme heat, the substrate expands to a greater degree than the AR surface, resulting in fissures across the lens surface. Consider a balloon covered with an extremely thin layer of plaster. When air is added to the balloon, the balloon expands but the plaster does not, and the plaster cracks. To avoid heat crazing AR lenses when adjusting frames, remove lenses prior to adjusting frames in a heating device then re-insert lenses after adjusting the frame.

-- Pete Hanlin, ABOM, LDO, training and development manager, Essilor Lens Group

 

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