The mechanical properties of the human lens capsule following capsulorhexis or radiofrequency diathermy capsulotomy

J. E. Morgan, R. B. Ellingham, R. D. Young and G. J. Trmal
Bristol Eye Hospital, England.

OBJECTIVE: To quantify the biomechanical properties of the capsulotomy edge following continuous-tear circular capsulorhexis (CTCC) or radiofrequency (RF) diathermy capsulotomy. METHODS: A test apparatus was constructed that allowed controlled stretching of capsulotomy edges following CTCC or RF diathermy capsulotomy. The lens contents were removed by phacoemulsification to permit the implantation of probes that exerted a test force on the capsulotomy edge and were moved in diametrically 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 subsequently examined by scanning electron microscopy. RESULTS: The capsulotomy edge produced by CTCC was significantly stronger (P < .001) than that following 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 (+/-SD) increase in the capsulotomy circumference was significantly greater with CTCC at 53% +/- 14.5% compared with RF at 18% +/- 8.5% (P < .001). Scanning electron microscopy disclosed a smooth edge for the CTCC capsulotomy. In contrast, multiple irregularities were seen in the edge following 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.