Effect of lens thickness and nuclear density on the amount of laser fragmentation energy delivered during femtosecond laser–assisted cataract surgery

Abstract

Purpose To study the influence of lens thickness and nuclear density on the amount of laser fragmentation energy delivered during femtosecond laser–assisted cataract surgery. Setting Ain Shams University and Al-Watany Eye Hospital, Cairo, Egypt. Design Retrospective case series. Methods This study included eyes of patients with primary cataract of different nuclear densities that had femtosecond laser–assisted cataract surgery using the Catalys Precision system. Variables studied included preoperative lens thickness measured by spectral-domain optical coherence tomography, nuclear density using the Lens Opacities Classification System III, pupil size, laser fragmentation energy, total laser energy, and transversal ultrasound time (Ellips FX). Patients were divided according to the preoperative lens thickness as follows: lens thickness more than 4.8 mm (Group 1) and lens thickness 4.8 mm or less (Group 2). Results The study included 192 eyes of 120 patients. The amount of laser energy for fragmentation was statistically significantly higher in Group 1 than in Group 2 (5.9 J ± 1.5 [SD] versus 4.5 ± 1.8 J) (P < .001). Laser fragmentation energy and total laser time had a strong positive correlation with lens thickness (r = 0.53, P < .001) but not with nuclear density or pupil size. Lens thickness was positively correlated with age (r = 0.42, P < .001) but not with nuclear density. Conclusions The preoperative lens thickness, not density, determined the amount of laser energy delivered. The laser might deliver unnecessary energy for softer and thicker nuclei while delivering less energy for thinner but harder nuclei.