Selection of appropriate phaco settings imperative for success

Experienced cataract surgeons discuss popular surgical techniques and how refining power and vacuum settings can improve outcomes.

Phacoemulsification settings can greatly affect the safety of the procedure as well as visual outcomes. The levels of ultrasound power and vacuum needed to perform successful cataract surgery vary dramatically, depending on the surgical technique being used.

Ocular Surgery News spoke with several expert cataract surgeons who are adept at performing three popular techniques: “divide and conquer,” “stop and chop” and “phaco chop.” Sources discussed the advantages of these methods, their personal phaco settings and how beginning surgeons can fine-tune their own settings.

Louis D. “Skip” Nichamin

“The basic rule of thumb is to work at whatever fluidic setting achieves the most efficient lens removal at that stage of the surgery. But here’s the caveat: without creating unnecessary turbulence or surge,” OSN Cataract Surgery Section Member Louis D. “Skip” Nichamin, MD, said. “Except when we’re sculpting, we generally strive to have the highest fluidic settings that we can safely manage. For example, when evacuating chopped segments, we want to utilize flow for followability and max-out on vacuumto provide holding capabilities. The rate limiting factor becomes turbulence and post-occlusion surge.”

The upper threshold of vacuum depends on several factors, he said, including the phaco platform, the pump system, tubing compliance, needle caliber design, and incision size and leakage.

“Phaco settings come down to personal preference,” Dr. Nichamin said. “The surgeons responsible for refining the various techniques can offer their own settings to aspiring surgeons who can then modify them further. It’s a starting point that allows novice surgeons to emulate the same intraocular milieu, and then as they gain experience, tailor the settings to their own personal preferences.”

Divide and conquer

Uday Devgan

In the divide-and-conquer approach, surgeons use high phaco energy to score the nucleus with two grooves in the shape of a plus sign. After this sculpting phase, the lens is then mechanically broken into four segments and removed, OSN Cataract Surgery Section Member Uday Devgan, MD, FACS, said.

“You primarily use energy to cut the grooves into the nucleus. But then when you are ready to remove the segments, you want higher vacuum and higher flow so those pieces can come to your phaco tip,” he said.

Terence Devine, MD, has been performing divide and conquer for several years.

“I’ve done chopping techniques, and the ultimate goal is much the same: You want to reduce the nucleus into smaller pieces,” he said. “But if you’re just chopping, once you’re done dividing the lens into smaller pieces, you still haven’t removed any of the nucleus. Whereas with divide and conquer, the first step is to create a deep groove right through the middle of the nucleus. So you now have removed a substantial portion of the nucleus while it’s still in the bag and as far away from the cornea as possible.”

The advantage is that the ultrasound power is not applied near the cornea, he said.

“Also, by working in the posterior chamber and doing the emulsification directly against the nucleus, you’re allowing it to absorb a lot of the energy. So the nucleus is in direct contact with [the energy] as opposed to working in the iris plane or the anterior chamber,” he said.

“Another advantage is that you don’t need to use a large side-port instrument, like a chopper. I just use a Sinskey hook. Therefore you can reduce the size of the side-port incision to 0.5 mm. That minimizes leakage, which stabilizes the chamber, and it also heals perfectly and minimizes the chance of endophthalmitis,” he said.

Dr. Devine performs divide and conquer on all of his patients, regardless of small pupils, intraoperative floppy iris syndrome or partially subluxed lenses.

Micropulse offers fluidic innovation by Andy Moskowitz OSN STAFF WRITER Surgeons have long used a combination of fluidics and power modulation to remove cataractous lenses from the eye. While these two aspects of phacoemulsification are commonly regarded as separate issues, a recent advancement in power modulation is making it harder to isolate power from fluidics, William J. Fishkind, MD, told Ocular Surgery News. William J. Fishkind “Power and fluidics are merging,” he said. “Micropulse phaco is, in a sense, a power modification and a fluidics modification. It has a major influence on the fluidics side of the machines.” Micropulse is a power setting with extremely short alternating bursts of power and rest periods, Dr. Fishkind explained. Typically, innovations in power settings center around preventing thermal damage to the endothelium, but micropulse is “changing the way that pieces are managed at the tip” by allowing pre-occlusion phacoemulsification, Dr. Fishkind said. Occlusive phaco vs. pre-occlusion phaco In typical occlusive phaco, the phaco tip is occluded as it holds onto a nuclear fragment, blocking flow through the phaco needle and causing the vacuum to rise, Dr. Fishkind explained. “There’s a pent-up high vacuum there that’s ready to act, and the minute that the surge disappears, the vacuum’s going to go right to that preset, so fluid is going to flow like crazy,” he said. Once the fragment clears the phaco tip, there is a real risk of post-occlusion surge, he said. However, micropulse phaco, by enabling pre-occlusion phaco, “allows material to stay close to the phaco tip but not totally occlude it. So when you phaco a fragment, it never totally occludes, you never get the vacuum building to its maximum preset, you never get the flow stopping, and therefore you don’t get the occlusion and you don’t get the surge,” he said. The micropulse power setting is patented by Advanced Medical Optics and is available in its Signature platform, as well as in the Stellaris (Bausch & Lomb) and Infiniti Vision System (Alcon), Dr. Fishkind said. In the Signature, he added, AMO has improved micropulse with a feature called ICE (Improved Control and Efficiency.) “It’s little kick of power at the beginning of the power cycle that pushes material away from the phaco tip. It helps keep the lens pieces close to but not adherent to the tip and helps to foster pre-occlusion,” he said. “And Alcon has gone to torsional. Torsional is totally pre-occlusion phaco.” For more information: William J. Fishkind, MD, FACS, is a clinical professor of ophthalmology at the University of Utah. He can be reached at 5599 N. Oracle Road, Tucson, AZ 85704; 520-293-6740; fax: 520-293-6771; e-mail: wfishkind@earthlink.net. Andy Moskowitz is an OSN Staff Writer who covers all aspects of ophthalmology.

Stop and chop

Dr. Nichamin performs the stop-and-chop method on ultra-hard cataracts, which account for about 1% to 2% of his cases, he said.

The method is similar to divide and conquer. Surgeons first apply phaco power to sculpt and weaken the nucleus before separating it mechanically into segments.

“Before we commence chopping, we first create a central limited but deep bowl, essentially sculpting out the core of the rock-hard nucleus. What that affords us is that our first chop will be carried out on a much weaker structure,” Dr. Nichamin said.

Surgeons use higher power settings during the sculpting phase with lower flow and vacuum and then switch to higher levels of vacuum when removing the chopped segments.

“The difficulty in trying to primarily chop a rock-hard lens is that, not only is it extraordinarily dense, it is typically extremely large. The amount of physical energy needed to divide the lens can, unfortunately, impart damaging energy to the zonules and capsule. If one were to first de-bulk the central nucleus, yet leave enough peripheral nucleus to adequately impale the phaco needle, subsequent cleavage planes can be created using much less force and thereby imparting less trauma to the zonular capsular network,” he said.

Bottle height measurements often incorrect According to Terence M. Devine, MD, calculating bottle height is not as simple as checking the number on the machine’s panel. “Most surgeons set the bottle height on the panel, and a number comes up, 80 or 100 or 120 or whatever it is, and they think that’s the bottle height, and it’s not,” Dr. Devine said. “Remember, bottle height is measured from the fluid level and the drip chamber to the patient’s eye.” Phaco machines have an internal reference point that assumes the location of the patient’s eye. If the eye is actually higher or lower than this reference point, the number on the panel is incorrect, he said. If, for example, a surgeon sets the bottle height at 100 cm and unintentionally raises the patient’s eye 10 cm above the machine’s reference point, then the true bottle height is 90 cm. “Those reference points differ from one machine to another,” he said. “It’s a useful exercise to at least once get out the measuring tape and see where they’re really at compared to where the machine says it is for the normal sitting position.”

Phaco chop

For the other 98% of cases, Dr. Nichamin uses the straight phaco-chop method. The technique is also used by OSN Cataract Surgery Section Member I. Howard Fine, MD.

I. Howard Fine

“For chop settings, we use high vacuum and lower power. We embed the tip into the lens and hold it with high vacuum, which we call ‘lollypopping’ the lens. With the lens held in place, we then chop it and evacuate the pieces,” he said.

Dr. Fine pioneered a version of phaco chop and published a report in the Journal of Cataract and Refractive Surgery in 2001.

“We showed that with power modulations you could reduce the energy to less than 1/1000 of what had been used previously and do better with respect to clear corneas and uncorrected visual acuities in the immediate postop period,” he said. “After that, power modulations became a big issue. Lower power is where we were all headed. Chopping is an important way to achieve that because you use mechanical forces to disassemble the nucleus, rather than grooving and cracking with ultrasound energy. What we have achieved is basically low power, high vacuum removal of cataracts.”

Keeping a low level of ultrasound power is necessary to ensure a complete and quick visual recovery after surgery, Dr. Devgan said.

“Any phaco energy in the eye damages the corneal endothelium. Average cataract surgery causes 10% of the corneal endothelial cells to be lost. People start off with 3,500 cells/mm², but that number decreases with time. An 85-year-old person may have about 1,500 cells, and they need 800 to 1,000 cells or more for the cornea to stay clear. Any less than that and the cornea starts to decompensate, and then they need a transplant. So if you’re performing surgery on an 85-year-old patient with a dense cataract, you can easily push him over,” he said.

In younger patients, excessive phaco energy can delay visual recovery. “People want instant gratification with their vision,” Dr. Devgan said.

For more information:

• Uday Devgan, MD, FACS, can be reached at the Maloney Vision Institute, 19021 Wilshire Blvd. #900, Los Angeles, CA 90024; 310-208-3937; fax: 310-208-0169; e-mail: devgan@ucla.edu; Web site: www.maloneyvision.com. Dr. Devgan has no direct financial interest in the products mentioned in this article, however, he is a paid consultant for Advanced Medical Optics, Allergan, Bausch & Lomb, eyeonics inc., Ista Pharmaceuticals and Staar Surgical.
• Terence M. Devine, MD, can be reached at 1 Guthrie Square, Sayre, PA 18840; 570-888-5858; fax: 570-882-3236; e-mail: devine_terence@guthrie.org.
• I. Howard Fine, MD, can be reached at 1550 Oak St., Suite 5, Eugene, OR, 97401; 541-687-2110; fax: 541-484-3883; e-mail: hfine@finemd.com; Web site: www.finemd.com. Dr. Fine is a paid consultant for Advanced Medical Optics and Bausch & Lomb.
• Louis D. “Skip” Nichamin, MD, can be reached at Laurel Eye Clinic, 50 Waterford Pike, Brookville, PA 15825; 814-849-8344; fax: 814-849-7130; e-mail: nichamin@laureleye.com. Dr. Nichamin is a medical monitor for Bausch & Lomb.

Reference:

• Fine IH , Packer M, Hoffman RS. Use of power modulations in phacoemulsification. Choo-choo chop and flip phacoemulsification. J Cataract Refract Surg. 2001;27:175.

• Andy Moskowitz is an OSN Staff Writer who covers all aspects of ophthalmology.