Purpose: Classification and quantification of swirling lens fragments during phacoemulsification with or without using the capsulorhexis flap as an additional endothelial protective shield. Also, to determine the effects on endothelial cell count (ECC) and central corneal thickness (CCT) caused by fragments during cataract surgery. Methods: Patients with dense cataracts scheduled for surgery were randomized into study and control groups (2:1). In the study group, the anterior capsule ‘flap’ from the capsulorhexis was used as an endothelial protection shield during phacoemulsification. The control group underwent standard surgery. During surgery, intra-operative optical coherence tomography was performed to score swirling lens fragments that hit the corneal endothelium. CCT and ECC were measured at several time points before and after surgery. Results: In total, 176 fragments in 49 eyes of 49 patients came in contact with the corneal endothelium. The mean number of fragments was 2.8 in the study group and 4.8 in the control group. There was no statistically significant change of ECC between the groups. Mean CCT increased by 16.6 µm in the study group and by 42µm in the control group 1 day postoperatively. There was no significant difference between the groups regarding the increase in CCT. Conclusions: No significant benefit concerning ECC or CCT was found in the study group compared to the control group, meaning that we were not able to prove that using the capsulorhexis flap as a protection shield is a sufficient method of protecting the corneal endothelium.