Elasticity of the Capsulorhexis and Delivery of the Nucleus

Abstract

OBJECTIVE:To study the stretching capacity of the capsulorhexis to determine the minimum diameter which will permit safe nucleus delivery in planned manual extracapsular extraction (ECCE). STUDY DESIGN: The stretching capacity of the capsulorhexis was measured by pulling up the two opposite sides of the anterior capsulotomy rim with two lens manipulator button hooks until the limit of stretching was reached and it ruptured. The procedure was videotaped and different measurements performed on the TV screen. Thirty-three human eye-bank eyes ranging from 11 to 82 years (mean 45.2 years) were used. Three age groups were selected; 11–27 years (mean: 18.9), 40–61 years (mean: 52.3), and 70–82 years (mean: 74.5). MAIN OUTCOME MEASURES: The diameter of the lens before capsulotomy, diameter of the unfilled capsular bag, and diameter of the capsulorhexis were measured before and after delivery of the nucleus. The perimeter of maximum circumference nucleus section, minimum oval nucleus section, and oval nucleus section tilted 30° were calculated. The perimeters of the unstretched and maximally stretched capsulorhexis were also calculated. RESULTS: The mean increase in stretched borderline perimeter, relative to the unstretched one, was 65.7%. These values were different in the three age groups studied, the younger group having a significantly higher mean increase in elasticity (75.9%) with respect to the other adult group (60.8%) and older group (58.4%). According to these results the diameter of a capsulorhexis between 4.0 and 5.5 mm could be increased to allow delivery of a nucleus of 8.3 mm through its smaller or larger section. CONCLUSION: Considering the stretching capacity of the capsulorhexis when suitable manoeuvres were performed to permit the release of the nucleus, through one of its lesser elliptical sections, an anterior continuous circular capsulotomy of 4.5 ± 0.5 mm in diameter should theoretically be sufficient to deliver almost all nuclei.