The hydrodissection is critical for freeing the adhesion between the capsule and lens cortex.  The hydrodissection cannula has a flattened tip to force the spread of fluid in the plane of dissection.  To achieve true cortical cleavage the tip must be placed just under the edge of the capsule. The fluid wave can be observed to pass behind the nucleus to opposite where the fluid wave was started.  A second hydrodissection can be performed 90 degrees to the first wave.  Evidence of adequate dissection can be seen as a slight rising of the nucleus and gentle rotation.