RESISTANCE OF THE HUMAN POSTERIOR LENS CAPSULE AND ZONULES TO DISRUPTION

Purpose: To determine the resistance of the human posterior lens capsu le and zonules to disruption during cataract surgery. Setting: Wet lab at Walkergate Hospital, Newcastle upon Tyne, England. Method: Human d onor eyes were obtained after removal of a corneoscleral disc. lens ex traction was performed by an extracapsular technique leaving an intact capsular bag. The resistance bi the zonules and posterior capsule to disruption by aspiration was measured in each eye, and the resistance of the zonules to damage from direct mechanical stretch was determined . Results: Posterior capsules tolerated a median suction pressure of 2 00 mm Hg (range 150 to 300 mm Hg) before disruption. Values for female eyes were slightly greater than for male; no significant correlation with age was shown. The zonular fibers tolerated a median suction pres sure of 200 mm Hg (range 150 to 300 mm Hg). The median mechanical zonu lar stretch tolerance was 3.00 mm (range 2.75 to 4.00 mm). No signific ant correlation was found between zonular suction tolerance or stretch tolerance and sex or between suction tolerance and age, but a negativ e relationship was noted between maximum tolerated stretch and age. Co nclusion: Setting the maximum aspiration pressure during irrigation/as piration to 150 mm Hg should help prevent capsular or zonular rupture. If more powerful aspiration is required, it should be used with great care so as not to engage the capsule.