THE MECHANICAL-PROPERTIES OF THE HUMAN LENS CAPSULE FOLLOWING CAPSULORHEXIS OR RADIOFREQUENCY DIATHERMY CAPSULOTOMY

Objective: To quantify the biomechanical properties of the capsulotomy edge following continuous-tear circular capsulorhexis (CTCC) or radio frequency (RF) diathermy capsulotomy. Methods: A test apparatus was co nstructed that allowed controlled stretching of capsulotomy edges foll owing CTCC or RF diathermy capsulotomy. The lens contents were removed by phacoemulsification to permit the implantation of probes that exer ted a test force on the capsulotomy edge and were moved in diametrical ly opposite directions using computer-controlled stepping motors. The magnitude of the force was measured during the capsule stretch, which allowed precise determination of the degree of capsular distention at the time of capsular rupture. Selected capsular edges were subsequentl y examined by scanning electron microscopy. Results: The capsulotomy e dge produced by CTCC was significantly stronger (P<.001) than that fol lowing RF. The mean (+/-SD) force to achieve capsule rupture was 0.15/-0.06 N with CTCC compared with 0.02+/-0.01 N with RF. The mean (+/-S D) increase in the capsulotomy circumference was significantly greater with CTCC at 53%+/-14.5% compared with RF at 18%+/-8.5% (P<.001). Sca nning electron microscopy disclosed a smooth edge for the CTCC capsulo tomy. In contrast, multiple irregularities were seen in the edge follo wing RF. Conclusions: Continuous-tear circular capsulorhexis provides a stronger capsulotomy and is the preferred method in routine cataract surgery. However, RF diathermy capsulotomy may have a useful role in conditions unfavorable to the safe completion of CTCC.