When the iris prolapses through the incision, it is due to one principal issue: a gradient whereby the pressure behind the iris is higher than in front of it. There are other factors which influence this such as iris tone (or lack thereof such as in floppy iris syndrome) or a poorly constructed incision, but still the pressure gradient is required to cause the iris prolapse.
One way of equalizing the pressure gradient is to increase the pressure in front of the iris by injecting viscoelastic. This does balance the posterior pressure temporarily, but once the viscoelastic is washed away, the iris prolapses again.
A better approach is to release the pressure gradient which is often caused by trapped fluid. In this case, the hydro-dissection caused an increased pressure within the capsular bag. By using the cannula to tilt the nucleus out of the bag, we immediately eliminated the pressure gradient and the iris was easily reposited back in to the anterior chamber, where it remained throughout the case. Note that this did cause a loss of some pigment from the posterior part of the iris at the sub-incisional area. While this is seen on retro-illumination due to the microscope settings, it fortunately did not result in any symptoms.
Click below to learn how iris prolapse was tamed at the beginning of surgery: