Eyeworld

Optimizing machine settings for routine, complex, and femto phaco cases 2 Experts share phacodynamics fundamentals valuable to all cataract surgeons, regardless of their experience levels A s fluidics and ultra- sound priorities evolve during the stages of phacoemulsification, it is essential to under- stand the phacodynamics of the process. Phacoemulsification ma- chines must be powerful enough to remove cataracts, but the ante- rior chamber must remain stable. "We need to prevent surge, and we always want to minimize damage to the cornea and decrease heat production," said Bonnie An Henderson, MD, clinical professor of ophthalmology, Tufts Univer- sity School of Medicine, and in private practice with Ophthalmic Consultants of Boston. Peristaltic versus venturi pumps Phacoemulsion systems rely on peristaltic and venturi pumps. Peristaltic pumps enable surgeons to set vacuum limits independent of flow (Figure 1). "You can access high vacuum limits and have a moderate flow and low vacuum, so you can have greater safety with thermal production," she said. However, surgeons need to understand what is happening so they can adjust flow and vacuum separately. "The venturi pump is not occlusion dependent, so you can actually have vacuum without occluding the tip," Dr. Henderson said (Figure 2). The venturi pump can have a rapid rise time. Pieces follow the flow to the tip in the center of the eye and can be vacuumed without full occlusion. However, flow de- pends on the vacuum level. Surge can be controlled with a higher bottle height, deepening the chamber, or with a reduced aspiration flow rate or vacuum preset. Some machines have auto- matic systems that help prevent surge or an aspiration bypass port allowing flow to continue when the tip is occluded, Dr. Henderson explained. Understanding phacodynamics Figure 2. Venturi pump advantages and disadvantages Source: Bonnie An Henderson, MD • Advantages • Not occlusion dependent • One variable to change • Rapid rise time • Can keep tip in center, pieces follow • Disadvantages • Flow dependent on vacuum level Figure 1. Peristaltic pump advantages and disadvantages Source: Bonnie An Henderson, MD • Advantages • Can set vacuum limits independent of flow • Access to high vacuum limits • Allows for moderate flow with low vacuum to increase thermal safety during sculpting • Disadvantages • Need to adjust both flow and vacuum limit to optimize settings " Our goal is to remove a cataract using enough power to be efficient, but not using more power than necessary. " Lisa Park, MD Peristaltic pump vacuum and flow Flow pumps directly control flow and indirectly control intraocular pressure (IOP) and vacuum. If there is no pump flow with an open-pinch valve, the bottle height controls the IOP; when the flow pump starts, there is flow into the anterior chamber, which reduces the IOP in the anterior chamber, said Ken- neth L. Cohen, MD, Sterling A. Barrett distinguished professor, Department of Ophthalmology, University of North Carolina at Chapel Hill. At a low flow rate, IOP is reduced; the aspiration line pres- sure decreases. The differential between the 2 pressures moves the fluid, he explained. When flow increases, IOP decreases more, and a negative pressure, vacuum, occurs in the aspiration line, increasing this differential. With partial occlusion, the flow decreases into the anterior

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