Perioperative pupil size in low-energy femtosecond laser-assisted cataract surgery

Abstract

Purpose: To assess potential changes in pupil size during femtosecond laser-assisted cataract surgery (FLACS) using a low-energy laser system.

Methods: The pupil sizes of eyes undergoing FLACS were measured using the Ziemer LDV Z8 by extracting images from the laser software after each of the following steps: application of suction, lens fragmentation, and capsulotomy. Furthermore, the pupil diameters were measured based on preoperative surgical microscope images and after releasing the suction. Paired t-test and the two one-sided tests (TOST) procedure were used for statistical analyses. The horizontal and vertical pupil diameters were compared in each of the steps with preoperative values.

Results: Data were available for 52 eyes (52 patients, mean age 73.4 years, range 51-87 years). The equivalence between mean preoperative pupil size and status immediately after femtosecond laser treatment was confirmed (p<0.001; 95% confidence interval [-0.0637, 0.0287] for horizontal and p<0.001; 95% CI [-0.0158, 0.0859] for vertical diameter). There was statistically significant horizontal and vertical enlargement of pupil diameters between 0.15 and 0.24 mm during the laser treatment steps as compared with preoperative values (all p values <0.001).

Conclusions: No progressive pupil narrowing was observed using low-energy FLACS. Although a suction-induced, slight increase in pupil area became apparent, this effect was completely reversible after removing the laser interface.

Fig 1. Illustration of the difference in magnification when observing the pupil through the cornea (a) by microscope through the air–cornea interface versus (b) during liquid interface laser docking.

Fig 2. Changes in pupil diameters at different time points of low-energy Femtosecond-Laser-Assisted Cataract Surgery (FLACS) using the Ziemer LDV Z8.

Boxplots showing the vertical (a) and horizontal (b) pupil diameters (median, quartiles, minimum, and maximum) before surgery, immediately after application of suction, after completion of lens fragmentation, after completion of laser capsulotomy, and after release of suction.

Fig 3. Differences in the measures of the horizontal diameter (a) and vertical diameter (b) of the pupil before surgery and at the time point “released suction,” each measured on the same subject.

The mean differences and the 95% confidence intervals of the differences are within the equivalence range [−0.2, 0.2].