Pressure instability could explain pumping phenomena in cataract surgery

Instability in the pressure line could explain the pumping phenomena sometimes reported during cataract surgery, according to Carlos Verges, Jorge Cazal and Cosme Lavin of the Department of Ophthalmology, Institut Universitari Dexeus, Barcelona, Spain.

The researchers' aim was to analyse pre- and post-occlusion changes in pressure-volume using a collapsible artificial anterior chamber connected to the Sovereign ICE console. The phacoemulsification irrigation and aspiration tubes were connected to a compliant artificial anterior chamber, and digital recordings of chamber pressure and volume were performed during pre-occlusion, occlusion and post-occlusion terms.

Each of the three different flow rates (20, 28 and 35 ml/min) used during pre-occlusion recorded a stable line without pumping phenomena being observed. Occlusion showed a spike of increased pressure with a tendency to restore the basal line with differences in pressure and time depending on the vacuum preset. There were two distinct steps on the post-occlusion graph: first the chamber pressure drops depending on the flow and vacuum parameters, never reaching negative values and then a pressure increase occurs restoring the basal line. With a flow setting of 35 ml/min and vacuum level of 400 mmHg, it showed a tendency to increase the pressure over the basal line, with two or three waves more until the basal line recovery.

Verges and his co-workers believe that the collapsible anterior chamber model is able to accurately show variations in pressure-volume related to events that occur in a real eye during cataract surgery. They found that instability in the pressure line was only recorded when there is high vacuum and high flow during post-occlusion recovery. This instability could explain the pumping phenomena reported during cataract surgery.

Ophthalmology Times Europe reporting from the XXIV Congress of the ESCRS, London, 9-13 September, 2006.