July 2010

 

CATARACT/ IOL

 

Options abound: phaco for everyone


by Matt Young EyeWorld Contributing Editor

 

 
MICS performed with the Infiniti system (Alcon, Fort Worth, Texas); incision size 0.7 mm

Implantation of a MICS IOL (Acritec 48S; Carl Zeiss, Dublin, Calif.): incision size 1.65 mm.

Source: Jorge L. Alió, M.D.

Bimanual micro-incision cataract surgery (MICS) is once again going head-to-head with micro-coaxial phacoemulsification surgery in research with new technology in the mix: torsional phaco. The research, published online in February in Acta Ophthalmologica, finds torsional favors the micro-coaxial approach but still works well with both types of procedures. “Torsional ultrasound is more efficient and has less incision injury in micro-coaxial phacoemulsification than in bimanual phacoemulsification,” reported study co-author Yizhi Liu, M.D., Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China. “However, visual rehabilitation and endothelial cell loss were comparable in both phaco groups.”

A closer look

Researchers analyzed 42 patients who underwent bimanual phacoemulsification with a torsional modality and 40 patients who underwent micro-coaxial torsional phaco. Micro-coaxial phaco inched ahead over rival bimanual significantly in terms of ultrasound time (57 seconds versus 85 seconds, respectively), cumulative dissipated energy (10 versus 14), and balanced salt solution volume (55 mL versus 75 mL). Ultrasound time and phacoemulsification energy are gauges of how efficient the ultrasound procedure is, wrote Dr. Liu, who then suggested a reason why micro-coaxial came out ahead in these regards. “We attribute this disparity to the low vacuum levels used (250 mm Hg) during phacoemulsification,” Dr. Liu reported. “In the bimanual phaco group, wound leakage is necessary to cool off the sleeveless phaco tip, yet the leakage can also lead to anterior chamber instability to some extent. To maintain the anterior chamber stability and avoid intraoperative complications, low vacuum level was required in bimanual phaco. With low vacuum and aspiration rates, more ultrasound time and energy are needed during the phacoemulsification process; thus, torsional ultrasound efficiency is reduced accordingly.”

But there were many important similarities between the groups. “There were no significant differences between eyes in preoperative CDVA [corrected distance visual acuity], central/temporal corneal thickness or endothelial cell density,” Dr. Liu reported. “No intraoperative anterior chamber collapse, posterior capsular tear, vitreous loss, retained lens fragments or wound burns occurred.”

Although endothelial cell damage has been linked to factors such as ultrasound time and energy levels—which again were favored by the micro-coaxial approach—endothelial cell loss was comparable between the groups at three months. “Only more ultrasound time and energy might not result in more endothelial cell loss when considering the multifactorial effects on endothelial damage,” Dr. Liu reported. At day one post-op, there was no significant difference in CDVA or central corneal thickness. “Temporal corneal thickness was statistically significantly thicker in [the] bimanual phaco group,” Dr. Liu noted. “At 30 days, there were no statistically significant differences in CDVA, central/temporal corneal thickness or endothelial cell density between two groups.”

Why would temporal corneal thickness manifest as thicker in the bimanual group? “We believe that several reasons (such as mechanical stress of the phaco tip, relatively tight incision, and increased incision temperature because of the sleeveless phaco tip) could cause incision endothelial cell damage and poor wound apposition, resulting in severe incision edema in bimanual phaco,” Dr. Liu reported. “In comparison, the corneal incision in micro-coaxial phaco [was] faced with less mechanical and thermal damage and ended with mild to moderate incision edema after surgery.”

Notably, previous research reported corneal wound burns with bimanual torsional surgery in as many as four of five cadaver eyes. However, that research used a 12 cc per minute aspiration rate, while this study used a 35 cc per minute aspiration rate. “The high aspiration flow rate results in rapid fluid turnover; thus, the incision temperature is greatly reduced, and the wound burn is avoided consequently,” Dr. Liu noted. “Our results indicate that torsional ultrasound is safe for bimanual and micro-coaxial phacoemulsification under suitable fluidic settings.”

Meanwhile, Robert H. Osher, M.D., professor of ophthalmology, University of Cincinnati, and medical director emeritus, Cincinnati Eye Institute, Cincinnati, said torsional phacoemulsification is a huge step forward in the evolution of the procedure. “If surgeons thinks it’s not enormously helpful then they’re misguided,” Dr. Osher said. “Up until now traditional longitudinal phaco has caused a great deal of repulsion. But torsional is unassociated with repulsion. It also has other advantages like a lower heat profile as a result of eliminating the to-and-from motion.” Dr. Osher suggested torsional provides for twice the efficiency of traditional ultrasound. That said, Dr. Osher is a bigger fan of micro-coaxial with torsional phacoemulsification than bimanual torsional phaco. He doesn’t like the fact that the metal bimanual tip rubs up against the incision, for instance, and believes the incisions are not as competent as with micro-coaxial phacoemulsification. “But I think we will always be going smaller and smaller [with incisions], and [bimanual] will get better,” Dr. Osher said.

Editors’ note: Dr. Liu reported no financial interests related to this study. Dr. Osher has financial interests with Alcon (Fort Worth, Texas).

Contact information

Liu: yizhi_liu@yahoo.cn
Osher: 800-544-5133; rhosher@cincinnatieye.com

Options abound: phaco for everyone Options abound: phaco for everyone
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