Chemical impurities and contaminants in different silicone oils in human eyes before and after prolonged use

Intraocular silicone oil (SiO) impurities as low molecular weight components (LMWC) and residual catalysts are thought to cause ocular toxicity. A case-control study was initiated to determine if highly purified SiOs of equal viscosity from two different manufacturers had a similar chemical stability after prolonged clinical use as a vitreous substitute in patients.

Medical grade samples of AcriSilOl 5000 (ASO 5000) and Vitreocrom 5000 (VC 5000) were obtained. Gas chromatography/flame ionisation detection (GC/FID) analyses were used to detect and characterize the LMWC (D4-D7 Siloxane fractions) and quantify the cholesterol level in the extracted SiOs as well as in the original SiO samples.

The concentration levels of LMWC D4 and D7 fractions of the original SiO samples already showed a significant difference (p < 0.05) preoperatively. After removal, SiO samples of ASO 5000 showed an absolute and relative decrease in all LMWC concentrations, except for the D6 values. Samples of VC 5000 had a significant decrease in the mean D4 concentration level, whereas the mean D5, D6, D7, and total LMWC values increased. The cholesterol increased as well within all SiO probes, but no significant differences between the two SiO types were found.

As cholesterol concentrations increased and LMWC D4 decreased similarly in both SiO brands, their stability might be regarded as equal. The smallest LMWC molecules (D4) appear to have the greatest capability to diffuse into the surrounding ocular tissues. The low grade of emulsification (12.9 %) in our patients could not be related to LMWC or cholesterol changes.