New method for measuring capsulorhexis resistance to tearing

This study describes a new model for mechanically measuring the resistance of the continuous curvilinear capsulorhexis (CCC) to tearing in human cadaver eyes. The model uses the entire capsular bag, which is isolated from the eye after complete evacuation. Other mechanized methods of assessing CCC strength use excised anterior capsules or partially phacoemulsified crystalline lenses, which the authors say yield lower tension strength values. The main objective of this new method is to simulate forces that the capsular bag-CCC edge may withstand during phacoemulsification maneuvers, such as hydrodissection, chopping, cracking and IOL implantation. With femto-phaco coming, this is going to be very important.

The authors tested 23 donor eyes a mean of 69.04 hours after death. 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 mm intervals to stretch the CCC to its rupture point.

The results of this testing found a mean CCC diameter of 5.3 ± 0.12 mm, mean load of 0.39 ± 0.16 N and mean extension at CCC tearing of 5.85 ± 1.17 mm. There was a moderately strong negative correlation between donor age and load (P = 0.0018).

The authors conclude that the testing method they describe may facilitate assessment of the biomechanical properties of the CCC edge and small differences between various anterior capsulotomy techniques.