Experimental model of intravitreal injection techniques.

PURPOSE: To evaluate the amount of drug reflux and vitreous leakage from the needle tract after various intravitreal (IVT) injection techniques in porcine cadaver eyes.
METHODS: The reflux after IVT injection was quantified by methylene blue injection through the pars plana of fresh pig eyes (0.05 mL per eye, n = 150) and the vitreous incarceration measured after balanced salt solution (BSS) IVT injection (0.05 mL per eye, n = 150) into eyes with vitreous previously stained with methylene blue. Blue spots observed on the ocular surface after injection quantified both reflux and vitreous incarceration. We tested different needle sizes (27, 30, and 32 gauge) and different techniques (depth and speed of injection). We used an ocular endoscope to observe the flow and diffusion of injected methylene blue and the vitreous incarceration at the puncture site after IVT injection using the different techniques.
RESULTS: Thirty-gauge needles showed less drug reflux than the 32-gauge or 27-gauge needles (P < 0.01). Thirty-two-gauge needles demonstrated less incarceration of vitreous at the tract site (P < 0.01), but with the endoscope, all needle tracts showed vitreous incarceration at their internal aspect. Deep IVT injection showed less reflux than superficial IVT injection, but vitreous incarceration did not differ. The delay between the scleral puncture and the injection did not modify the reflux or the vitreous incarceration.
CONCLUSION: Thirty-gauge needles and deep placement of the needle tip into the vitreous before injection may reduce reflux and vitreous incarceration. This could maximize the therapeutic effect of IVT injection and may decrease the rates of severe complications such as retinal detachment and endophthalmitis.