Mechanized model to assess capsulorhexis resistance to tearing

Purpose: To evaluate a model of mechanically measuring resistance to tearing of a continuous curvilinear capsulorhexis (CCC) using the entire capsular bag of fresh human cadaver eyes isolated from the eyes after complete evacuation.

Setting: John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA.

Design: Experimental study.

Methods: After the cornea and iris were removed, a 5.0 to 5.5 mm anterior CCC was created. The nucleus was hydroexpressed and the capsular bag evacuated by irrigation/aspiration. A pair of metal shoetree-shaped fixtures, designed based on human lens geometric dimensions, were implanted separately in the capsular bag and assembled together with a screw nut. After complete zonulectomy, the fixture-capsular bag assembly was removed from the eye and loaded onto a mechanical tester. The fixtures were separated at a velocity of 7.0 mm/min in 0.15 μm intervals to stretch the CCC to its rupture point. Rupture load (N) and extension were measured and graphed.

Results: Testing of 23 donor eyes a mean of 69.04 hours ± 22.72 (SD) after death showed the following mean values: CCC diameter, 5.3 ± 0.12 mm; load, 0.39 ± 0.16 N; extension at CCC tearing, 5.85 ± 1.17 mm. There was a moderately strong negative correlation between donor age and load (P = .0018).

Conclusions: Previous mechanized methods of assessing CCC strength used excised anterior capsules or partially phacoemulsified crystalline lenses, yielding lower tension strength values. This force-displacement method may facilitate assessment of small differences between anterior capsulotomy techniques.