Intravitreal drug dispersion and needle gauge

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Intravitreal injections (IV) have become the main treatment for many ocular diseases. At present, IV are supplied with a 27G, 30G needles. Reduced ocular discomfort and scleral penetration forces have been reported after using smaller gauge needles. However, smaller inner diameter implies increased fluid speed and intraocular turbulence that may result in retinal harm


IV were injected with 0.05 mL Indian ink using 27, 30 and 32 G needles. After the injection the eyes were divided in groups and the vitreous was photographed. Three masked observers scored Indian ink dispersion within the vitreous gel from 1 (completely localized) to 4 (complete dispersion).


Intra-observer and inter-observer reproducibility was between 0.78 and 0.95 and between 0.93 and 0.95, respectively (intra-class correlation coefficient). The average Indian ink dispersion scores for 27, 30 and 32 G needles were 3.4, 2.5 and 1.8 respectively (p=0.07 for 27 vs. 32 G; p= 0.71 for 27G vs. 30G; p=0.15 for 30G vs. 32G; Student t test for unpaired data)


The inner flow is four times faster in thinner needles, considering that the plunger slides with similar speed. We might expect that flow through the thinner needle would induce more turbulence within the vitreous gel; however, the pattern of intravitreal distribution of Indian ink suggests that the injected fluid and the turbulence were confined to a small bag in the area where smaller gauges were used. The results of this work suggest that 32G needles do not increase turbulence of injected fluid. Limited turbulence may be of even greater interest in elderly eyes with liquefied vitreous gel, reducing mechanical retinal damage

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