Preoperative opacification of acrylic intraocular lenses in storage

The preoperative opacification of acrylic intraocular lenses (IOLs) was investigated in order to determine its cause. Opacified IOLs were examined by energy dispersive X-ray (EDX), the buffer solutions were analysed by inductively coupled plasma optical emission spectroscopy (ICP-OES) and the rubber seals used in the bottles in which the IOLs were stored were ashed and tested. The deposit covering the opacified lenses contained a significant amount of zinc, which was absent from fresh IOLs and buffer solution. The source of this was found to be the rubber seals used to seal the glass bottles in which the IOLs were stored. There were two types of rubber seals used, red and grey in colour. The buffer solutions in which opacification had occurred was also contaminated with zinc, but this was only noticeable when using the red seals. This contamination was reproduced by boiling red seals in fresh buffer solution for eighty minutes, to simulate autoclaving. It was concluded that zinc from the zinc oxide used as filler in the rubber seals was leaching into the buffer solution and causing the IOLs to become opacified. This was found to be much worse in the case of the red seals than for the grey ones. However, minute crystals were found on the IOLs stored using the grey ones, which could potentially act as nucleation points for postoperative opacification.