We work in a very tiny space of just a fraction of a milliliter: the volume of the anterior chamber is about 250 microliters (0.25 ml) and even if we add the volume of the posterior chamber, we are still under 1 ml. In this space we are constantly infusing fluid as we aspirate the cataract material, creating a delicate balance. And in some situations, there can be factors which will disrupt this balance and put the posterior capsule at risk for damage.
If there is surge, when the inflow of fluid is temporarily outstripped by the outflow of fluid, even for just a fraction of a second, the posterior capsule can come into contact with the metal phaco tip and rupture. This, of course, creates many complications such as vitreous prolapse, insufficient support for the IOL. We can adjust the phaco parameters to create more inflow and less outflow, but we also need an added measure of safety.
Using the smooth, backside of the chopper allows up to set up a barrier to keep the posterior capsule away from the metal phaco tip. This is especially important when aspirating the last nuclear piece because nothing is then weighing down the capsular bag. In this video, the patient has posterior pressure and the added challenge of a small anterior segment.
Click below to learn the technique of using the chopper to protect the capsular bag: