Transvitrectomy injection of low-viscosity substances

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Sir, Ghosh et al.1 present three cases of inadvertent trypan blue injection into the subretinal space and suggest an alternative safer method of injection into the vitreous cavity using a backflush flute. Low-viscosity substances such as stains, triamcinolone, and heavy liquids are commonly used during vitrectomy surgery. We would like to suggest an alternative method of injecting any of these substances—that of injection through the vitrectomy probe itself. A three-way tap is inserted into the distal split point in the aspiration tubing of the vitrectomy probe and a syringe containing the low-viscosity substance is attached (Figure 1). To allow injection, the three-way tap is turned to close off the aspiration line to the vitrectomy pump and the substance injected via an assistant, with the surgeon directing the port of the probe to the desired location. After injection, the three-way tap is again turned off to the line, allowing active aspiration from the eye. Figure 1 Three-way tap turned towards aspiration line for transvitrectomy injection. The advantages of the system are that the injection is directed through the side port of the probe and hence not directly towards the retina, thus reducing the risk of subretinal injection. Furthermore, the injection can be directed to the area of interest, for example, peripheral membranes. There is no need to enter and exit the eye for injection or aspiration of the injected substance, thus reducing potential retinal tear formation and pathogen entry into the eye. A couple of points regarding the technique are worth observing. There is some dead space between the injection point on the three-way tap and the cutter port. With the set-up we have used this is ∼0.45 ml. This volume is irrelevant in terms of heavy liquids and diluted triamcinolone, but is more significant with low-volume membrane stains. We have, however, found that there is sufficient volume in the stains we have used to provide adequate staining. It is also important for the three-way tap to be primed with the infusion solution at the start of the case to avoid air injection during injection, which is important when injecting into a fluid-filled eye. In conclusion, this is a simple and safe technique that reduces instrument exchange and improves surgical flow.