Pre-occlusive technique increases safety over standard phaco

Pre-occlusion phacoemulsification reduces amount of vacuum rise during cataract surgery, eliminating post-occlusion surge.

Issue: July 1, 2005

ByErin L. Boyle

Micropulse phaco technology can be used to stop occlusion surge from occurring in cataract surgery, increasing the safety of the procedure, according to William J. Fishkind, MD.

Dr. Fishkind devised what he calls the pre-occlusion phaco (POP) technique to minimize vacuum rise. For nearly 3 years, he has performed the POP technique using the WhiteStar technology on the Sovereign by Advanced Medical Optics with positive results. He said many surgeons most likely already use a similar technique when performing cataract surgery but do not have a term for it.

“POP means better control, more comfort during the phaco, less phaco power delivered to the anterior segment, less surges, less trampolining of the posterior capsule, and less torn capsules and vitrectomies – ie, better control,” Dr. Fishkind said. “Postoperatively, the corneas are clearer, there’s less endothelial cell loss, more rapid stabilization of vision.”

All of these factors together mean the POP technique provides a greater degree of safety compared to standard phaco techniques, Dr. Fishkind said. By decreasing the amount of power delivered to the anterior segment, the amount of damage to the endothelium and the blood aqueous barrier is decreased, while surgeon control is increased. He said that by eliminating surge the chamber stays more stable, resulting in fewer torn posterior capsules and vitrectomies.

Two images of a fragment adjacent to a phaco tip. Though the pictures are similar, note the difference in dynamics. In the left image, the vacuum is approaching the preset limit of 250 mm Hg and there is no flow. In the right image, with the POP technique, the vacuum is 107 mm Hg with a preset limit of 250 mm Hg, and there is aspiration flow.

Images: Fishkind WJ

“It turns out that if one thinks about what governs the way one does cataract surgery, surge becomes a major consideration in the quality of the procedure and the comfort the surgeon has in doing the procedure and, indeed, the number of complications – ie, torn posterior capsules, subsequent damage to the vitreous face and vitrectomy,” Dr. Fishkind said. “They all tie together.”

Occlusion phases

According to Dr. Fishkind, the fluidics of phaco can be thought of in three phases: pre-occlusive, occlusive and post-occlusive.

In the typical occlusive mode of phaco, the phaco tip is occluded as it holds onto a nuclear fragment, he said. The fragment blocks flow through the phaco needle, causing the vacuum to rise. When the surgeon applies phaco power, the fragment is emulsified and aspirated. The most dangerous part of the procedure is when the fragment clears the phaco tip and the occlusion is broken, Dr. Fishkind noted, leading to post-occlusive surge.

“Once sculpting is done and we’re working on fragments, when the fragment comes to the phaco tip, it occludes the tip. When it occludes the phaco tip, vacuum goes to its maximum preset and flow goes to zero,” Dr. Fishkind explained. “If a surgeon then puts his foot on the foot pedal in phaco position 3 and applies phaco power, the power then emulsifies that fragment, and at the moment of emulsification inflow through the phaco needle exceeds the ability to fill the anterior chamber, and outflow through the phaco needle exceeds inflow into the anterior chamber. Therefore, the chamber shallows.”

The post-occlusive phase is initiated by the surge that shallows the chamber, he said. The degree of surge varies depending upon the setting, but it happens every time, he noted.

But in Dr. Fishkind’s POP technique, the rough transition from the occlusive to the post-occlusive phase is avoided. The surgeon starts to emulsify the nuclear fragment in the pre-occlusive phase, before achieving complete occlusion. Because the phaco tip is not occluded, the vacuum does not rise nearly as high, rendering post-occlusion surge impossible, he said.

“Now you can use lower amounts of power,” Dr. Fishkind said. “For example, using the Sovereign system, I never go over 30% power, even in the hardest of nuclei.”

Preventing surge

Many types of phaco tips on the market can be used for the POP technique, according to Dr. Fishkind. He said what sets his technique apart from others is the use of short micropulse bursts of ultrasonic power on the Sovereign with WhiteStar, which essentially holds the fragment of cataractous material thousandths of a millimeter away from the phaco tip.

“By holding it away, you never allow occlusion to occur, and therefore, you never allow surge to occur,” he said.

Occlusion is still used for some purposes, such as grasping large fragments that are in the equator of the capsular bag and moving them to the iris plane for emulsification.

“You want occlusion there. Occlusion isn’t a bad word,” Dr. Fishkind said. “It’s just at this step, during emulsification of fragments, that’s when we want to switch to pre-occlusive phaco.”

The technique requires a great deal of cavitational energy and probably some jackhammer effect, Dr. Fishkind said. Also, there is a summation of the phaco tip movement and the fragment movement, he said, allowing phaco efficiency to rise and rendering it easer to emulsify harder fragments in less time with less power.

For Your Information:
William J. Fishkind, MD, is a clinical professor of ophthalmology at the University of Utah, Salt Lake City. He can be reached at 5599 N. Oracle Road, Tuscon, AZ 85704; 520-293-6740; fax: 520-293-6771. Dr. Fishkind has a direct financial interest in the AMO Sovereign system and is a paid consultant for AMO.
Erin L. Boyle is an OSN Staff Writer who covers all aspects of ophthalmology.