Abstract
Purpose :
Trocar cannulas have gained widespread use in retinal surgery but have never been studied for gas or air injection in pneumatic retinopexy. The purpose of this study is to assess the potential effectiveness of trocar cannulas in producing more consistent large air bubbles and minimizing small bubbles during intravitreal air injection.
Methods :
Intravitreal injection of air was performed on 36 porcine eyes split into three study groups: 1) standard technique using a 27-gauge needle, 2) a 27-gauge straight cannula in a 27-gauge valved trocar and 3) a 30-gauge cannula in a 27-gauge valved trocar. 0.4 mL of air was injected intravitreally into each eye. Intraocular pressure (IOP) was measured immediately following injection using a Tono-Pen XL (Reichert, NY USA). The number of intravitreal air bubbles after injection was counted by two observers (JG and MC). Two-tailed t-tests were used to assess for the difference in IOP and in the number of intravitreal air bubbles after injection.
Results :
Intravitreal injection using the 27-gauge needle resulted in a mean IOP of 25.6 mmHg and 1.83 intravitreal air bubbles. 6/12 (50%) of the injections resulted in one large air bubble. Mean IOPs were significantly lower after intravitreal injection using the 27-gauge cannula (10.3 mmHg, p < 0.0001) and the 30-gauge cannula (12.8 mmHg, p = .0002) compared to needle injection. The mean number of intravitreal air bubbles produced using the 27-gauge cannula (2.67, p = .319) and the 30-gauge cannula (2.92, p = .169) was not significantly different when compared to the 27-gauge needle. 6/12 (50%) of the 27-gauge cannula and 3/12 (25%) of the 30-gauge cannula injections resulted in one large bubble.
Conclusions :
Post-injection IOPs were significantly less when using a trocar cannula compared to a 27-gauge needle for intravitreal air injection. Air may have leaked out of the trocar-cannula interface, during cannula removal, or during trocar removal, which may have caused the lower IOPs. These lower IOPs after trocar cannula injection likely correlated with a smaller volume of air that remained in the vitreous cavity, which suggests that there is no advantage to utilizing this method to improve the likelihood of single large bubble formation. However, lower IOP might reduce the need for paracentesis, which is often required following the procedure.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.