Comparison of Maximum Stretch Forces between Femtosecond Laser-Assisted Capsulotomy and Continuous Curvilinear Capsulorhexis

Abstract

The current study reports comparing the postoperative mechanical properties of the anterior capsule between femtosecond laser capsulotomy (FLC) and continuous curvilinear capsulorhexis (CCC) of variable size and shape in porcine eyes. All CCCs were created using capsule forceps. Irregular or eccentric CCCs were also created to simulate real cataract surgery. For FLC, capsulotomies 5.3 mm in diameter were created using the LenSx® (Alcon) platform. Fresh porcine eyes were used in all experiments. The edges of the capsule openings were pulled at a constant speed using two L-shaped jigs. Stretch force and distance were recorded over time, and the maximum values in this regard were defined as those that were recorded when the capsule broke. There was no difference in maximum stretch force between CCC and FLC. There were no differences in circularity between FLC and same-sized CCC. However, same-sized CCC did show significantly higher maximum stretch forces than FLC. Teardrop-shaped CCC showed lower maximum stretch forces than same-sized CCC and FLC. Heart-shaped CCC showed lower maximum stretch forces than same-sized CCC. Conclusively, while capsule edge strength after CCC varied depending on size or irregularities, FLC had the advantage of stable maximum stretch forces.

Figure 1

Representative shapes of irregular-shaped continuous curvilinear capsulorhexis (CCC). Three types of irregular CCC—heart-shaped (a), teardrop-shaped (b) and eccentric (c)—are shown. (d), (e), and (f) show the location of 2 jigs pulling capsule edges (arrows).

Figure 2

Images of the capsule stretch experiment. Two L-shaped jigs are inserted into the capsule opening (a); one side is pulled at constant speed (b).

Figure 3

Comparison of capsule opening circularity among the FLC group and the small CCC, middle CCC, and large CCC subgroups. There were no significant differences among the groups. FLC: femtosecond laser capsulotomy; CCC: continuous curvilinear capsulorhexis.

Figure 4

Results of the capsule stretch experiments. Association between stretch distance and stretch forces during the capsule stretch experiments in the CCC group (a) and FLC group (b) is shown. There were large variations in maximum stretch force and maximum stretch distance within the CCC group, while there was less variation in the FLC group in this regard. The average maximum stretch force and the coefficient of variation (CV) in each group are shown (c). There were no differences in mean stretch force between the CCC group and the FLC group (d). However, the middle CCC subgroup showed higher stretch forces than the FLC group (e). ^∗p < 0.05.

Figure 5

Comparison of circularity (a) and stretch force (b) among the CCC subgroups and the FLC group. The heart- and teardrop-shaped CCC subgroups showed significantly lower circularity than the middle CCC subgroup and FLC group. The maximum stretch force in the teardrop-shaped CCC subgroup was significantly lower than those in the middle CCC subgroup, FLC group, and eccentric CCC subgroup. The maximum stretch force in the heart-shaped CCC subgroup was significant lower than that in the middle CCC subgroup. ^∗p < 0.05, ^∗∗p < 0.001, and ^∗∗∗p < 0.0001.

Figure 6

The correlation between eccentric distance and maximum stretch force in the eccentric CCC subgroup. There was a significant negative correlation between eccentric distance and maximum stretch force (r = −0.7785, p = 0.0279).