Customizing the settings for cataract surgery leads to improvements in both surgical safety and efficiency. This strategy implies operating in a manner that provides you with greater control and minimizes wasted effort or time. Although the available technologies differ by manufacturer, the general principles by which you can manipulate these technologies to improve safety and efficiency are similar.
ANALYZING THE VARIABLES
You can customize two main attributes of phaco technology: (1) the fluidics of the procedure and (2) the delivery of phaco energy.1 Fluidics is affected by vacuum level, rise time/flow rate, and infusion pressure or bottle height. Phaco energy can be varied through changes in tip design or by manipulating the time interval, direction (horizontal or longitudinal), or stroke length that is delivered.
Phaco settings may be customized depending on the lens’ density, for a particular surgical situation such as pseudoexfoliation or a shallow anterior chamber, or for a specific surgical technique such as chopping or divide and conquer.
The goals of customizing fluidics include achieving sufficient holding power (ie, vacuum) to allow for the efficient removal of nuclear material; maintaining a deep, stable chamber; limiting fluid flow; and preventing postocclusion surge. Alterations in fluidics that improve the mechanics of one of these goals have the potential to alter one or more of the others.
Although the aspiration flow rate and vacuum levels may be adjusted, surgeons rarely consider changing bottle height as a way of customizing phaco settings. In certain clinical settings, however, the bottle height should be varied. For example, in the setting of a zonular dialysis or capsular rupture, lowering both the bottle height and flow rate will allow you more control. Conversely, the occasional patient cannot lie flat and has to undergo surgery while seated or semi-recumbent. In such cases, it is worth recalling that the reference point for zero height of the infusion bottle is the tray on the phaco machine. The bottle is therefore artificially lowered by whatever height the patient’s head is above the phaco machine’s tray. In this case, the bottle can be raised additionally with either an extension pole or separate IV pole, or the flow rate has to be reduced accordingly.
Raising the bottle height tends to produce a deeper and more stable chamber. When combined with appropriate incision construction and phaco tip design, fluid outflow through the incision can still be minimized.
The rate at which “things” occur depends on your using the fluidics of the particular phaco system. By speed, most surgeons are actually referring to how quickly nuclear material can be brought to the phaco tip. Many will instinctively assume that this speed is related to vacuum, but the rate at which things occur depends on the type of pumping system used.
Either you vary the flow rate or the vacuum limit, depending on whether you are using a flow-type pump (peristaltic) or a direct-vacuum pump (venturi/ diaphragm). The former directly controls the flow of fluid out of the eye with a higher pumping speed to create a greater flow rate. Many surgeons refer to this concept as the aspiration flow rate. With flow pumps, vacuum is not created until the phaco tip is occluded by cataractous material. Shorter rise times to maximum preset vacuum levels are achieved with higher flow rates. With a venturi or direct-vacuum pump, you can set the vacuum limit. Again, vacuum is not created until the tip is occluded. Then, the vacuum will build at a rate that is proportional to the vacuum limit.
In addition to the efficient attraction of nuclear material to the tip, customizing fluidic settings achieves two other related efficiencies. Higher vacuum settings improve holding power, which decreases retropulsion and leads to the more efficient use of phaco energy. Higher vacuum levels also increase your ability to remove nuclear material with vacuum alone by mechanical deformation and shearing of the lenticular material at the phaco tip.
By hastening the movement of lenticular material to the phaco tip, higher flow rates and vacuum speeds should be a beneficial adjustment, because they will allow you to perform surgery more expeditiously and with fewer extraneous movements. Balancing the advantages of greater rapidity is that the phaco tip will also attract both the posterior capsule and iris with greater ease. Again, these undesirable effects can be minimized by alterations in fluidics as well as the machine’s and system’s design.
Modern phaco platforms all employ sophisticated sensors and/or strategies to minimize postocclusion surge. These include decreasing the pumping speed or vacuum limit as maximum levels are achieved, venting the vacuum system, and using stiffer, low-compliance tubing. All of these measures permit higher vacuum levels while maintaining stable chambers.
Phaco Energy’s Delivery
Early-generation phaco machines had a simple way of customizing the delivery of energy: it was either on or off, with 100% delivery of energy via machine control. Modern phaco systems allow you to vary the amount of energy delivered, the time intervals for the energy’s delivery delivery and cessation, and even the direction of energy’s delivery (horizontal vs longitudinal). Customizing these variables is directed toward maximizing the efficiency with which nuclear material is removed while minimizing retropulsive forces and the total energy delivered to the anterior segment.2,3
HOW DO YOU PHYSICALLY ALTER AND CUSTOMIZE YOUR SETTINGS?
Because each cataract procedure can have its own nuances, it can be difficult to assess how much an alteration in any of the aforementioned parameters affected a specific change in your surgical experience. One approach to customizing settings is to begin with either your current settings or the manufacturer’s suggested ones and then to vary them by 10% at a time. After each incremental change, perform five to 10 surgeries to allow intraindividual case experiences to even out and then evaluate how the new settings are or are not helping to improve efficiency. If the adjustments prove beneficial, then you can again increase them by 10% and repeat the process. Digital or video recording of these surgeries can greatly enhance the evaluative process.
By using this incremental approach, you can achieve significant gains in safety and efficiency. After three iterations of these changes, because of compounding, you will have achieved a greater than 30% alteration in your phaco settings. At this point, it can be helpful to compare the 30%+ settings to your original settings so that you can fully assess any improvements in safety and efficiency.
Modern phaco machines allow surgeons to adjust multiple parameters to perform surgery with both improved safety and efficiency. A broad understanding of these parameters along with incremental adjustments will allow the individual surgeon to customize the phacoemulsification such that it is best suited to his or her technique and the specific patient.
Richard Tipperman, MD, is a member of the active teaching staff at Wills Eye Hospital in Philadelphia. Dr. Tipperman may be reached at (484) 434-2716; firstname.lastname@example.org.
- Packer M,Fishkind WJ,Fine IH,et al.The physics of phaco:a review.J Cataract Refract Surg.2005;31(2):424-431.
- Chen M,Sweeney HW,Luke B,et al.A retrospective randomized study to compare the energy delivered using CDE with different techniques and Ozil settings by different surgeons in phacoemulsification [published online ahead of print July 14,2009].Clin Ophthalmol.2009;3:401-403.
- Zeng M,Liu X,Liu Y,et al.Torsional ultrasound modality for hard nucleus phacoemulsification cataract extraction [published online ahead of print June 20,2008].Br J Ophthalmol.2008;92(8):1092-1096.