Even when a 32-gauge needle was used, intravitreal injection posed a risk of introducing contamination directly into the eye. However, of all the needle gauges studied, the 27-gauge needle posed the greatest risk.
Japanese researchers used two experimental models of vitreous contamination in enucleated porcine eyes to detect and measure the introduction of such contamination into the eye after intravitreal injection. They published the results of their study in the October, 2016, issue of Retina.
In one experimental model, the researchers applied fluoresbrite carboxylate microspheres to the surface of the conjunctiva to detect the introduction of contamination into the eye during intravitreal injection. They then injected a solution of saline, 0.05 mL, into the eye by using a 27-gauge (G), 30-G, or 32-G needle. They used an intraocular fiber catheter to monitor the injections.
In another experimental model, the researchers applied condensed microspheres to an excised sheet of porcine sclera, then injected a solution of saline, 0.05 mL, from the top of an applied microsphere through the sclera and collected a sample. They used fluorophotometry to measure the fluorescence strength of the samples.
The researchers detected fluorescent microspheres in all 10 eyes injected with 27-G needles. In contrast, they detected these microspheres in 9 of 10 eyes injected with 30-G or 32-G needles. Furthermore, they found significantly greater fluorescence strength in the 27-G needle group than in the 30-G or 32-G needle groups (P < 0.01 for both comparisons).
In addition, they found significantly greater quantification study values for all needle gauges than for controls (P < 0.01).
In light of these findings, the researchers concluded that, even when a 32-G needle was used, intravitreal injection posed a risk of introducing contamination directly into the eye. However, they concluded that the 27-G needle posed the greatest risk of contamination of all the needle gauges they studied using these experimental models.