Intraocular lens changes after short- and long-term exposure to intraocular silicone oil. An in vivo study

Silicone oil frequently is used as a vitreous substitute after complex vitreoretinal procedures. The authors sought to study the effect of short- and long-term exposure to silicone oil on polymethyl methacrylate (PMMA, MC60BM; Alcon, Ft. Worth, TX), silicone (SI-30NB; AMO, Irvine, CA), and soft acrylic (MA60BM; Alcon) intraocular lenses (IOLs).

An experimental animal study.

Forty-one New Zealand white rabbits underwent lensectomy, vitrectomy, capsulotomy, and placement of one of the three types of IOLs into the ciliary sulcus. All lenses were weighed before implantation and 24 hours after explanation. In the short-term study, an fluid-air exchange was performed followed by the use of silicone oil (1000 centistokes) to coat the posterior lens surface. Immediately thereafter, an air-fluid exchange was performed and the remaining silicone on the posterior lens surface was aspirated or wiped or both for 1 minute using a soft-tipped extrusion cannula for 1 minute. In the long-term study, the posterior segment was filled with 1000 centistokes silicone oil after fluid-air exchange. Animals were observed by slit-lamp biomicroscopy and photographed at 1 week, 1 month, and 3 months after surgery. At 3 months, all animals underwent silicone-fluid exchange, an attempt to manually remove any remaining silicone oil, and lens explanation.

In the short-term study, no silicone oil remained after manual wiping and/or aspiration in any of the four rabbits implanted with PMMA or acrylic IOLs. In the animals with silicone IOLs, a significant amount of silicone oil remained on the posterior lens surface of all lenses (P < 0.01 for silicone vs. acrylic and silicone vs. PMMA). No statistically significant difference was found when comparing the lens weights in each group before and after implantation. In the long-term study, aqueous droplet formation was found on the posterior lens surface of six of nine PMMA IOLs and ten of ten silicone IOLs at 3 months. No opacities were observed in the group with acrylic IOLs (P < 0.001 for acrylic vs. silicone, P = 0.0018 for acrylic vs. PMMA, and P = 0.047 for PMMA vs. silicone). Adherent silicone oil remained on two of nine PMMA IOLs and on none of ten acrylic IOLs. In contrast, a significant amount of silicone oil remained on the posterior lens surface of ten of ten silicone IOLs (P < 0.001 for silicone vs. acrylic and silicone vs. PMMA). Furthermore, there was a statistically significant increase in lens weights before and after implantation in the silicone IOL group but not in the PMMA or acrylic group (P < 0.01).

It is extremely difficult or impossible to remove remaining silicone oil from the posterior surface of a silicone IOL after short- or long-term exposure to silicone oil. This oil may interfere with the surgeon's view of the retina and may diminish the patient's visual acuity. In contrast, oil is readily removed from the posterior surface of an acrylic IOL. The authors therefore recommend the use of a soft acrylic or PMMA IOL over a silicone IOL when choosing a lens for implantation in patients who may require vitreoretinal procedures with silicone oil tamponade.