Accuracy, Precision, and Residual Volume of Commonly Used Syringes for Intravitreal Injections and the Impact on Intraocular Pressure.

PURPOSE: To compare accuracy, precision, and residual volume of commonly used syringes for intravitreal injections (IVIs) and to assess the intraocular pressure (IOP) rise by variations in volumes delivered. DESIGN: Experimental laboratory study. SUBJECTS: No subjects were involved in this study. METHODS: We tested 8 syringe models with 2 different needle setups, with 2 different solutions (distilled water or glycerin) and target volumes (50 and 70 µL). To obtain the delivered and residual volumes, we weighed the syringe-needle setups with scale before liquid withdrawal, with liquid, and after liquid release. We also created an experimental eye model to determine the transient rise in IOP following stepwise 10-µL increases in injection volumes. MAIN OUTCOME MEASURES: Delivered and residual volumes, IOP rise. RESULTS: We tested a total of 600 syringe-needle setups. Becton Dickinson (BD) Ultra-Fine (0.34 ± 0.28 µL), Zero Residual (1.53 ± 1.15 µL), and Zero Residual Silicone Oil-free (1.40 ± 1.16 µL) syringes showed the lowest residual volume (P < 0.001) in comparison with the others (range: 24.86 ± 1.78 µL for Injekt-F to 51.97 ± 3.37 µL for Omnifix-F). The most accurate setups were (percentage deviation from target volume): Zero Residual Silicone Oil-free (+ 0.70%), Zero Residual 0.3 ml (+ 4.49%), BD Ultra-Fine (+ 7.83%), Injekt-F (9.42%), Norm-Ject (+ 15.88%), Omnifix-F (+ 16.96%), BD Plastipak Brazil (+17.96%), and BD Plastipak Spain syringes (+ 19.41%). There was a statistically significant difference between the Zero Residual Silicone Oil-free syringe and all other syringes (P < 0.0001), except for the Zero Residual 0.3-ml syringe (P = 0.029). The coefficient of variation was low for all syringes. The modeled IOP rise ranged from 32.3 (standard deviation [SD], 1.4) mmHg for 20-µL injection volume to 76.5 (SD, 1.0) mmHg for 80-µL injection volume. For the standard 50-µL injection volume, the peak pressure was 50.7 (SD, 0.1) mmHg, and the pressure rise duration was 28 (SD, 2) minutes. CONCLUSIONS: There were significant differences in accuracy and residual volume between syringes, whereas they showed a high precision. Volume excess results in a considerable increase in IOP rise after injection. These findings may provide a relevant overview to clinicians and to both device and drug manufacturers regarding pharmacoeconomic, safety, and efficacy issues. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

A Multi-Lumen Glaucoma Stent With Titratable Pressure-Lowering Effect: A Proof of Concept Study.

Purpose: To explore the feasibility of a glaucoma stent with a titratable pressure-lowering effect. Methods: This was an in vitro study. We created a resin stent with a micro-precision three-dimensional printer. It represented a cylinder with one primary and two secondary lumina. The inner opening of each secondary lumen was sealed with a membrane. We used a surgical eye model to simulate implantation of the stent and a laser procedure analogous to argon laser trabeculoplasty (ALT) to ablate each membrane. To study the fluid dynamics, we used a high-precision syringe pump and measured the steady-state pressure for one, two, and three lumina in parallel at flow rates of 2.5, 5.0, and 10.0 µL/min. Results: The stent could be implanted into the eye model and visualized in the anterior chamber angle. Coloring the membrane facilitated laser membranotomy, and a 0.1-second laser pulse with 250-mW power was enough to ablate one membrane. The steady-state pressure for one lumen increased linearly with increasing flow rate, in accordance with the Hagen-Poiseuille equation. Two and three lumina in parallel decreased the pressure by factors of 2.1 and 3.2, respectively, in accordance with the electronic-hydraulic analogy and Ohm's law applied to parallel resistors. Conclusions: The study presents proof of concept for a glaucoma stent with multiple lumina, which can be separately opened with an ALT-like procedure to induce a predictable, stepwise increase in pressure-lowering effect. Translational Relevance: The glaucoma stent in this experimental study can be reproduced in a biocompatible material and further studied in vivo.