Strength of the lens capsule during hydroexpression of the nucleus.

In planned extracapsular cataract extraction, hydroexpression of the nucleus has been introduced to facilitate nucleus delivery when performing capsulorhexis. The hydroexpression technique induces a fluid pressure in the capsular bag, which may rupture the posterior capsule. In a human cadaver eye model the pressure at the capsule's rupture point was determined in 16 cadaver eyes and compared to the fluid pressure in the capsular bag during hydroexpression of the nucleus in 32 eyes. The posterior capsule was able to withstand a pressure of 59 +/- 10 mm Hg (mean +/- SD) without rupturing. During hydroexpression of the nucleus the pressure was less than 12 mm Hg (3 mm Hg to 12 mm Hg) when the diameter of the capsulorhexis opening was 5.5 mm or more (measurement in the anterior chamber). Thus hydroexpression of the nucleus seems to be a safe technique when the diameter of the capsulorhexis is 5.5 mm or more.