corneal endothelial cell loss after phacoemulsification in relation to hydrodynamic parameters: low versus high vacuum techniques

purpose: to evaluate the effect of vacuum and flow rate on endothelial cell loss after high versus low vacuum phacoemulsification. methods: this randomized clinical trial was performed on 60 eyes of 60 patients with moderate lens opacity (nuclear sclerosis 3+). all surgeries were performed by one experienced surgeon using stop and chop technique with sovereign white star machine (amo). patients were randomly assigned to high and low vacuum techniques in equal numbers. the machine was set on 400 mmhg vacuum and 40 ml/min flow rate in the high vacuum group and on 200 mmhg vacuum and 20 ml/min flow rate in the low vacuum group during the chop stage. all other parameters were similar in both groups. phacotime multiplied by average ultrasound power was defined as total ultrasound energy. specular microscopy was performed before and 1, 6 and 12 weeks after the operation. results: after 12 weeks, mean endothelial cell loss was 9.0±4.0% versus 9.6±4.6% in the low and high vacuum groups, respectively (p=0.6). mean ultrasound power was 9.2±4.3% and 13.1±4.6% in the low and high vacuum groups, respectively (p=0.001). mean phacotime was 1.28±1.0 minutes in the low vacuum group versus 0.88±0.6 minutes in the high vacuum group (p=0.04). total ultrasound energy and total fluid volume used (turbulence) during phacoemulsification was similar between the two study groups. total ultrasound energy was the most powerful predictor of endothelial cell loss (r2=0936, p=0.001), but turbulence was not a significant predictor (r2=0.924, p=0.1).  conclusion: no significant difference in endothelial cell loss was found between low and high vacuum techniques. this study supports advice to junior surgeons to choose lower hydrodynamic phaco machine parameters; experienced surgeons can choose higher parameters to reduce phacotime.