Minimizing Errors During Intravitreal Injections: Analysis of the Residual Volume of Various Small Coupled Syringes/Needles and Characterization of the Vitreal Reflux

Abstract

Purpose: : Drugs have been routinely administered through intravitreal injections (IVT) for the therapy of various vitreoretinal diseases. However, therapeutic flaws may arise, as the amount of intravitreal-injected drug may not be accurate for several reasons. The objectives of this study are: 1. to assess the residual volume (RV) within the syringe/needle after their empting; and 2. to analyze the amount and composition of vitreal reflux after IVT.

Methods: : Five different pairs (BD® syringe/needle) were weighed totally empty and filled in with 0.1mL of distilled water. After unloaded, they were weighed once more to assess the RV. These measurements were taken five times for each pair, using a high precision balance (Ohaus® AS-200, OHAUS, Pine Brook, NJ, USA). To analyze the amount and composition of the reflux, 0.1 mL of Trypan Blue (TB) (0.5mg/mL) was injected in enucleated pig’s eyes using 27, 30 or 31 gauge needles with tunneled or perpendicular incisions. Enucleated bovine eyes were also injected with 0.25ml of TB using 27 and 30 gauge needles with tunneled or perpendicular incisions. In both experiments, the amount of reflux was measured by the largest length of the reflux fluid, while a grading of 0 to ++++ was used to describe the presence of TB in the reflux. Procedures were done by the same examiner.

Results: : The RV analysis showed that the group 28G-12.7mmx0.3mL induced the smallest volume (0.62µL ± 0.15), while the 30G-8mmx1mL caused the largest RV (6.80µL ± 0.39)(p < 0.001). When the first pair was compared to 30G-12.7mm x 0.3mL group, the difference was not significant (p ≈ 1.0). Another insignificant difference (p = 0.07) was found between 29G-12.7mmx1mL (5.08µL ± 0.37) and 31G-8mmx0.5mL (5.38µL ± 0.10) groups. The results for the reflux studies are summarized in the table below.

Conclusions: : Long needles attached to smaller syringes may offer a smaller chance of RV after IVT in this experimental set-up. Analyzing the reflux, the gauge may be an important factor for both types of scleral incisions, although less reflux may occur with the tunneled type.

Keywords: injection • vitreoretinal surgery • drug toxicity/drug effects