Introduction

The presence of silicone oil (SO) droplets in the vitreous, even though frequently considered harmless, has been reported in 0.03–1.7% of eyes receiving intravitreal injections [1].

The source of these droplets is supposedly the syringes, since they are coated with SO in order to facilitate the gliding of the plunger [2]. However, it is uncertain the role the needles might have. Therefore, this study assessed whether two models of needles contained SO.

Materials and methods

One hundred samples each of two models of needles (Fig. 1) from the same manufacturer were studied: BD PrecisionGlide 26-gauge (Becton-Dickinson, Curitiba, Brazil, lot # 8234979, ref # 300110) and 30-gauge needle (lot # 8165866, ref # 990193). The metallic part of the needle was removed from the plastic hub. Groups of 50 samples were immersed in 50 mL of chloroform (99.8%, Anidrol, São Paulo, Brazil) for 30 min under ultrasound, 40 kHz (USC-4800, Unique, São Paulo, Brazil). Then the chloroform was evaporated in a water bath (TE-056, Tecnal, São Paulo, Brazil) followed by an oven (Q-314M212, Quimis, São Paulo, Brazil) at 105 °C. After cooling, the mass of the extract was verified by an analytical scale (AB204-S, Mettler Toledo, Switzerland). The dry extract was assessed by Fourier-transform infrared spectroscopy (Nicolet iS10, Thermo Electron Scientific Instruments, Madison, WI), with band ranging from 4000 cm−1 to 400 cm−1, resolution of 4 cm−1, and 32 scans.

Fig. 1
figure 1

BD PrecisionGlide needles. a 30-gauge needle; b 26-gauge needle

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Results

Analysis of the material indicated the presence of polysiloxane (i.e., SO) in both needles (Fig. 2). The following characteristic bands were found: 2960 cm−1, stretching vibrations of CH3 in Si-CH3; 1260 cm−1, bending vibrations of CH3 in Si-CH3; 1090 cm−1 and 1020 cm−1, asymmetric stretching vibrations of Si-O-Si; 800 cm−1, stretching vibrations of Si-C in Si-CH3 [3].

Fig. 2
figure 2

Fourier-transform infrared spectroscopy showing characteristic bands corresponding to polysiloxane, i.e., silicone oil, in both BD PrecisionGlide needles. a 30-gauge needle; b 26-gauge needle

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Both 30- and 26-gauge needles contained on average 1 and 1.5 mg, respectively, of polysiloxane for every 50 samples, yielding an estimate of 20 and 30 μg, respectively, per unit.

Discussion

SO is a lubricant commonly used in medical catheters, syringes, and needles to aid comfort during insertion and control during the delivery of medication. The main concern about SO in the eye is that it may cause symptomatic floaters. A report from the American Society of Retina Specialists showed that 5.2% of US retina specialists have performed vitrectomy to remove SO droplets after intravitreal injection of bevacizumab [4]. This is undesirable due to the inherent risks of invasive procedures.

Our suspicion for the presence of SO in needles follows from a separate study where we identified rare SO droplets in fluid ejected from a silicone-free syringe via a BD PrecisionGlide needle (unpublished data). The current analysis confirms that SO is present in two needle models; in other words, the use of silicone-free syringes does not completely eliminate the risk of SO droplets in the vitreous so long as the needle contains SO.

In conclusion, ophthalmologists should be aware that needles tend to be coated with SO and there is a potential risk of displacing some droplets into the eye.