Fluid dynamics in the vitreous chamber during infusion in ophthalmic surgery: a numerical study

We numerically investigate the fluid dynamics of the infusion of balanced salt solution into the vitreous chamber during ophthalmic surgery. A 25-gauge vitrectomy set consisting of an infusion cannula and a vitreous cutter is inserted in a realistic model of a human vitreous chamber. As the vitreous cutter aspirates at a constant flow rate (7.5–20 ml min−1 in the present study), the corresponding infusion flow generates a high-velocity laminar jet (1.00–2.65 m s−1) causing high stress on the retina (pressure up to 1200 Pa) and mixing. We analyse the Lagrangian coherent structures and quantify mixing. Results show a vortex ring around the jet impingement region, in the posterior part of the chamber. At higher infusion rates (Re > 600), interacting hairpin vortices emerge as a result of an instability in the vortex ring. This disordered flow enhances mixing, potentially dispersing substances such as vital dyes, with consequences on visibility and surgery time. We quantify the overall mixing and its evolution with height, observing a smooth transition from an ordered flow to an unsteady disordered one with the flow rate. These findings may pave the way towards strategies to minimise complications while optimising efficiency, especially given the trend towards minimally invasive surgery with progressively smaller infusion cannulas.