Anterior chamber stability during bimanual irrigation and aspiration: Theoretical and experimental analysis

Purpose: To determine the requirements for maintaining a stable anterior chamber during bimanual irrigation and aspiration (I/A) using side-port cannulas. Setting: Cole Eye Institute, The Cleveland Clinic Foundation, Cleveland, Ohio, USA. Methods: A theoretical fluid dynamic model of the closed I/A system was developed. Model predictions were compared with experimental flow measurements made on the Alcon Legacy 20000 system using a number of commercial and custom I/A cannulas. Results: Bore diameter, length, and orifice size determine the pressure-flow relationship of cannulas. Four of 18 tested irrigation cannulas were able to maintain anterior chamber stability when used with a 23-gauge/0.3 mm orifice aspiration cannula and maximum aspiration settings. All 4 had a 21-gauge lumen diameter. A shorter cannula length also contributed to higher flow. Conclusions: Anterior chamber stability during bimanual I/A required the irrigation system to have lower flow resistance than the aspiration system, which can be provided by using cannulas with larger lumen diameters and shorter lengths. Special cannula designs can provide these characteristics without requiring larger sideport incisions.