The use of silicone oil in vitreoretinal surgery may result in higher IOP levels. Photo: Alan Franklin, MD, PhD. Click image to enlarge.

Silicone oil is a commonly used vitreous substitute for complicated vitreoretinal cases, such as tractional retinal detachment or proliferative vitreoretinopathy, but certain complications associated with the polymer can be quite serious and result in glaucoma and anterior segment problems. Case reports have noted instances of silicone retinotoxicity with central vision loss and of subretinal and intracranial migration. “The removal of silicone oil is usually recommended as soon as possible to avoid or reverse these complications,” wrote the authors of a recent paper published in Acta Ophthalmologica. “However, in certain cases, removal of silicone oil is also associated with complications including recurrent retinal detachment and hypotony.”

“Although long-term complications of silicone oil tamponade after pars plana vitrectomy (PPV) have been known for quite [some] time, silicone oil remains one of the favorite agents for long-standing vitreous replacement,” the researchers wrote. “However, when discussing the safety of silicone oil as an endotamponade, the risk of complications cannot be neglected. A total of 921 adverse events associated with the use of silicone oil were reported in our analysis.”

Their review of literature published between 1994 and 2020 compared the complications associated with silicone oil use after PPV in patients with different underlying diseases. A total of 4,717 patients from 43 studies who received silicone oil and other vitreous tamponades, including placebo, during PPV were included in the analysis. “Our data were collected from studies published after 1994, when the FDA approved the use of silicone oil as a vitreous substitute,” the authors pointed out.

All studies made comparisons between silicone oil and other tamponades such as gases (SF6, C2F6, C3F8), heavy silicone oil or placebo. The researchers also included a secondary outcome to compare complication rates in terms of oil viscosity used (1,000 to 2,000 cst vs. 5,000 cst). Mean duration time before silicone oil removal was 4.35±3 months in their review. They reported significant differences between silicone oil and other agents, with regard to intraocular hypertension and retinal redetachment (RRD) rate. No differences were reported in other complication rates.

Here are some of the findings:

• A non-significantly higher emulsion rate was found in low viscosity silicone oil, with comparable complications in both groups.

• The difference between hypotony in both groups (2.76% of eyes filled with silicone oil) was not significant.

• There were no differences between low and high silicone oil viscosity (3.25% and 5.97% of patients reported hypotony, respectively).

• A majority of studies reported an 8% to 12% range for RRD recurrence after removal of silicone oil.

• RRD occurred in 14.6% of eyes filled with conventional silicone oil and in 17.81% of eyes filled with other agents. RRD risk was statistically significantly lower in silicone oil eyes, but this finding is in contrast with two previous studies.

• Cataract progression was reported in 42.7% of eyes filled with silicone oil.

• No significant differences in vision loss were found between patients with silicone oil and those with other agents, but the researchers noted that about 25% of PPV cases can lose vision postoperatively with any tamponade agent.

“The true incidence of ocular hypertension after silicone oil injection is difficult to ascertain because the baseline and intraoperative characteristics are diverse among patients included in the different analyses,” they wrote. “The reported incidence of raised IOP varies from 3% to 40% in patients receiving conventional silicone oil tamponade and from 14% to 30.7% in patients with heavy silicone oil. In this study, the risk of raised IOP after surgery in the silicone oil group and in the other tamponades was 15% and 10.87%, respectively. We found that silicone oil has a statistically significant greater effect on raising IOP than other agents.”

The researchers noted that the long-term IOP increasing effect of silicone may depend on the open-angle mechanism and presence of silicone oil in the anterior chamber. “[This] may contribute significantly to IOP increase, blocking the outflow pathway through the trabecular meshwork,” they explained.

The researchers concluded that there was a higher risk of raised IOP with silicone oil in different surgical histories. “This result should be more of a consideration when selecting silicone oil as an endotamponade in patients with a history of glaucoma,” they wrote. “It also demonstrates that silicone oil has favorable outcomes in terms of lower risk of RRD. In the risk of bad outcomes that can cause severe visual impairment, we didn’t find any differences. However, it’s still unclear when the silicone oil is required and how to use it efficiently to minimize the related complications.”