Efficiency of radiused, non-radiused tips for phaco explored in study

Take Home

Radiused and non-radiused phacoemulsification tips were equivalent in efficiency for removing lens fragments during micropulse longitudinal and transversal/longitudinal phacoemulsification procedures. Non-radiused tips were more efficient with torsional action.

A cataract case is presented using a radiused tip with aspiration of the posterior capsule, but no capsule break. (Video courtesy of William R. Barlow, MD)

By Lynda Charters; Reviewed by William R. Barlow, MD

Salt Lake City-A comparison of radiused and non-radiused phacoemulsification tips indicated that both were equivalent in efficiency for removing lens fragments when micropulse longitudinal and transversal/longitudinal (elliptical) phacoemulsification procedures were performed. Non-radiused tips were more efficient with torsional action.

“It has always been assumed that a radiused tip sacrificed efficiency in the name of safety,” William Barlow, MD, commented. “This study undermines that premise, showing that with elliptical and micropulse longitudinal phaco, a radiused tip is not inferior with respect to efficiency and may enhance both efficiency and safety.”

The radius (Dewey) tip has a rounded-edge design and the theory behind the design is that it reduces the risk of damage to accidentally aspirated ocular structures, such as the capsule and iris.

Dr. Barlow-assistant professor, John A. Moran Eye Center, University of Utah, Salt Lake City-recounted that the published rate of posterior capsule rupture in recent literature during procedures performed by residents is 3% to 7%, and for attending surgeons it is 1%. However, the concern is that radiused tips may reduce the efficiency of phacoemulsification by increasing phaco energy and surgical time, he explained.

In contrast, the non-radiused tip has a sharp edge. In theory, the sharp edge is better designed to cut and break down material, thus enhancing efficiency by reducing required phaco energy and surgical time.

Examining the study

An in vitro study published in June 2010 in the American Journal of Ophthalmology reported a significant (p <0.0001) reduction in the rates of capsular breakage when the radiused tip was used in cadaver capsules.

Dr. Barlow and colleagues conducted an in vitro laboratory study in which porcine lenses were harvested within 48 hours of arrival, hardened by soaking in formalin for 2 or 3 hours followed by soaking in balanced saline solution (BSS) for 24 hours. The lenses were cut into uniform 2-mm cubes, stored in BSS, and used within 36 hours, he said.

The lenses were treated in this manner because the investigators found in a previous study that following soaking in formalin, these lenses have properties similar to 3 to 4+ nuclear sclerotic human cataracts in crush and phacoemulsification properties, he explained.

The following parameters were used:

·      For all lenses, the flow rate was 40 mL/min with a bottle height of 50 cm with a peristaltic pump.

·      For torsional ultrasound using the Infiniti system (Alcon Surgical) with the Orzil torsional hand piece (0.9 mm, 30-degree bevel, 30-degree bend), the settings were 50% power (longitudinal), 100% amplitude (torsional), and 550 mm Hg vacuum.

·      For transversal/longitudinal blend ultrasound procedures using the AMO WhiteStar Signature phacoemulsification system with the Ellips Transverse Ultrasound hand piece (0.9 mm, 30-degree bevel, 30-degree bend), the settings were 550 mm Hg vacuum and 50% continuous power.

·      For longitudinal ultrasound, the WhiteStar Signature phacoemulsification system was used (0.9 mm straight tip with a 30-degree bevel), the settings were micropulse 50% power, 6 ms on and 12 ms off (duty cycle). 

An individual lens cube was placed inside a chamber filled with BSS and the time required for phacoemulsification of the cube was recorded. If the cube bounced from the tip during phacoemulsification, a “chatter” event was recorded. This was repeated 20 times for each experimental group.

Diving deeper

Dr. Barlow reported that for the torsional ultrasound procedures, there were significant (p <0.05 for both comparisons) differences in efficiency in favor of the non-radiused tip. With lenses soaked in BSS for 2 hours, phacoemulsification with the non-radiused tip took 1.18 ± 0.69 seconds and with the radiused tip 2.14 ± 1.94 seconds. With the lenses soaked for 3 hours, the respective times were 2.52 ± 1.99 seconds and 5.07 ± 4.2 seconds.

For the transversal/longitudinal blend ultrasound procedures, with the lenses soaked for 2 hours and 3 hours, there were no significant differences between the tip performances. In the lenses soaked for 2 hours, the respective times were 0.91 ± 0.54 and 0.90 ± 0.60 seconds, and with the lenses soaked for 3 hours, the times were 3.08 ± 2.29 and 2.97 ± 1.59 seconds.

For the longitudinal with micropulse ultrasound procedures, with the lenses soaked for 2 hours, the times were 1.29 ± 1.35 and 1.06 ± 0.63 seconds and with the lenses soaked for 3 hours 6.22 ± 4.91 and 5.00 ± 2.65 seconds.

There was no difference in chatter in any groups.

“The radiused tip was equivalent in efficiency and chatter events during the transversal/longitudinal blend and micropulse longitudinal procedures,” Dr. Barlow said. “There was a trend toward benefit with the radiused tip that did not reach significance.”

He pointed out, however, that with torsional ultrasound, the efficiency was significantly better with the non-radiused tip with no difference in chatter events.

Meaning behind the research

Why do these differences exist with some phaco modalities but not with others? Dr. Barlow suggested that “he difference in efficiency seen with the radiused tip between differing forms of phaco is likely related to the primary motion of the tip.

“With longitudinal motion, a sharp tip is not required to mechanically break down material, whereas with primarily torsional motion it appears that a sharp tip conveys an advantage with the shaving action that occurs with this motion,” Dr. Barlow said. “ Cavitational energy also may be more efficiently presented to material with longitudinal motion, and it is possible that a radiused tip may generate a greater amount of cavitation relative to a sharp tip with longitudinal action.”

William R. Barlow, MD

E: william.barlow@hsc.utah.edu

Dr. Barlow has no financial interest in any aspect of this report. The study was supported by an unrestricted grant from Research to Prevent Blindness, Inc. The tips were donated by Microsurgical Technology, Inc.