Equilibrium study of copper absorption to different types of soft contact lens

To measure binding affinity of copper, one of the heavy metals in particulate matter (PM) was applied to soft contact lenses made of two different materials because contact lenses are readily exposed to PM. Copper binding to ionized silicon hydrogel lens yielded an equilibrium association constant K_a,eq value of 14.03 μM without color change of lens, compared to that of 19.16 μM for copper binding to de-ionized hydrogel lenses with color change of lens. The results indicated that the color change of lens is not consistent with the concentration of cooper deposition on lens, and copper bound relatively stronger in ionized silicon hydrogel lens than in de-ionized hydrogel lens. Therefore, the continuous exposure of contact lenses to high PM levels might lead to heavy metal deposition on the lens, which would be detrimental to ocular health.