Purpose: This study aimed to quantify the amount of silicone oil (SO) released across a variety of syringe and needle models routinely used for intravitreal injection. Methods: The release of SO was assessed in eight models of syringes, two of which were reported to be 'SO-free', and eleven models of needles with unknown SO content. To evaluate SO release within the context of anti-VEGF therapeutics, syringes were evaluated using aflibercept, bevacizumab, buffer, ziv-aflibercept and formulation buffer. All syringe tests were performed with or without agitation by flicking for syringes. Needles were evaluated without agitation only. Samples were fluorescently labelled to identify SO, and triplicate measurements were collected using imaging flow cytometry. Results: Seven out of 8 syringe models showed a statistically significant increase in the SO particle count after agitation. The two SO-free syringe models (HSW Norm-Ject, Daikyo Crystal Zenith) released the least SO particles, with or without agitation, whereas the BD Ultra-Fine and Saldanha-Rodrigues syringes released the most. More SO was released when the syringes were prefilled with formulation buffer than with ziv-aflibercept. Syringes filled with aflibercept and bevacizumab had intermediate levels. Agitation increased the release of SO into each of the drug solutions. Silicone oil (SO) was detected in all needles. Conclusions: Agitation of the syringe by flicking leads to a substantial increase in the number of SO particles. Silicone oil (SO)-free syringes had the best performance, but physicians must also be aware that needles are siliconized and also contribute to the injection of SO into the vitreous.

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