Behaviour of the intraocular pressure during manual and vented gas forced infusion in a simulated pars plana vitrectomy

The purpose of the present is to measure and to compare the intraocular pressure (IOP) during manual and mechanical Perfluorodecalin (PFD) injection in 23 and 25-Gauge(G) simulated pars plana vitrectomy using a StellarisPC® vitrectomy system. A human eye model was developed and IOP recorded during infusion of PFD using three sensors, two located at the equator and one in an area corresponding to the macula (M) of the human eye. Three measurements were performed with 23 and 25G settings: during manual PFD injection by two vitreoretinal surgeons with different experience; during Venting Gas Forced Infusion (VGFI) of PFD at 8 psi and 12 mmHg of infusion; during VGFI of balanced salt solution at 30 mmHg of infusion in the closed eyeball model. The manual infusion of both surgeons (in particular that of the surgeon in training) showed IOP values significantly higher (p<0.0001) and more scattered than the VGFI. The average IOP recorded during VGFI at 8 psi and 12 mmHg was higher than the set one, with both 23G and 25G (29.03 and 27.56 mmHg respectively). In the closed eyeball model, the actual IOP was steady but higher than the 30 mm Hg set. In all the experiments, except for two observations, the IOP recorded at the sensor M was significantly higher than that at the equator. In conclusion, potential damage due to excessive IOP fluctuations can be minimized using the mechanical infusion. Mechanical infusion prevents sustained pressure overshoot but it introduces a systematic pressure offset.