Parameters affecting anterior capsulotomy tear strength and distension

Authors: Sheraz M. Daya, MD, FACP, FACS, FRCS(Ed),  Soon-Phaik Chee, FRCOphth, FRCS(Ed), FRCS(G), MMed(S’pore), Seng-Ei Ti, FRCS(Ed), MMed(S’pore),  Richard Packard, MD, FRCS, FRCOphth, David H. Mordaunt, PhD

Purpose

To study the effects of anterior capsulotomy diameter and discontinuity on tear threshold load and distension for the technique of continuous curvilinear capsulorhexis (CCC).

Setting

Singapore National Eye Centre, Singapore, and CapsuLaser Inc., Livermore, California, USA.

Design

Two separate randomized pairwise cadaver eye preclinical studies.

Methods

Capsulotomies were performed in 40 cadaver eyes of 20 donors using CCC. The pairwise comparisons were divided into 2 study groups: Study A: Continuous versus discontinuous capsulotomies; Study B: Capsulotomy diameter of 5.0 mm and smaller versus diameters of 5.2 mm and larger. A shoe-tree method was used to apply load to the capsulotomy rim, and the Instron tensile stress instrument measured threshold load and distension to initiate a capsular tear. Wilcoxon matched-pairs signed-rank tests were performed to assess statistical superiority.

Results

In Study Group A, all pairs demonstrated that continuous capsulotomies were better than discontinuous capsulotomies for both the anterior tear threshold load and distension (P < .01). In Study Group B, 80% of the pairs demonstrated that diameters of 5.2 mm and larger were better than those of 5.0 mm and smaller diameter (P < .05).

Conclusions

Anterior capsulotomies behave as nonlinear elastic (elastomeric) systems when exposed to an external load and distension. This study demonstrated that continuous circular capsulotomies were more resistant to anterior tears than discontinuous capsulotomies. A point of irregularity or a defect in a capsulotomy rim has a high probability of being the tear initiation point. Furthermore, larger diameter capsulotomies were more resistant to anterior tears than smaller capsulotomies.