Impact of lens density and lens thickness on cumulative dissipated energy in femtosecond laser–assisted cataract surgery

To evaluate the required cumulative dissipated energy (CDE) to fragment the crystalline lens in femtosecond laser–assisted cataract surgery (FLACS) in relation to lens density and lens thickness. Consecutive eyes that underwent FLACS between September 2014 and March 2017 by a single surgeon using in all cases the same femtosecond laser and phacoemulsification platform were included in our retrospective study. Prior to surgery, corrected distance visual acuity (CDVA), optical biometry corneal, and crystalline lens tomographies were performed to assess anterior chamber depth (ACD), axial length (AL), and crystalline lens parameters (i.e., lens density, thickness, and nucleus staging (NS)). After surgery, CDE was calculated and analyzed in relation to lens density (LD) and lens thickness (LT). Zero ultrasound expenditure cases were recorded and their occurrence analyzed. The chart review identified 236 eyes of 200 patients, 98 males and 102 females aged 65± 15 years which were included in the study. Mean LD was 11.26 ± 2.05 pixel intensity units (range 7.30–18.80), and the mean LT was 3417 ± 405.17 μm (range 2545–4701). LD and LT correlated moderately (r = 0.50, p < 0.001) and weakly (r = 0.23, p < 0.001), with post-laser CDE. Higher LD and LT were also associated with lower rates of zero phaco (eyes in which no phacoemulsification energy was necessary). Furthermore, NS (r = 0.528, p < 0.001) and CDVA (r = − 0.3524, p < 0.001) also correlated with CDE. Higher LD, LT, NS values, and low CDVA are associated with higher ultrasound expenditure (CDE—cumulative dissipated energy) and with lower rates of zero ultrasound expenditure during FLACS.