Preop cataract grading and phaco settings reduce energy use and fluid infusion

Less ultrasonic and fluidic energy in the eye minimizes potential for damage to the corneal endothelium and blood-aqueous barrier, author says.

Preoperatively customizing phacoemulsification parameters based on objective cataract density measurements significantly reduced phacoemulsification time and energy, according to a study.

Currently, many surgeons adjust phaco settings intraoperatively, according to study author Donald R. Nixon, MD, FRCSC, DABO, but adjusting these settings preoperatively based on cataract grading could be more efficient.

“I think the most important take-home message is that preoperatively adjusting your surgical parameters on your phaco system to reflect the grade of the cataract may in fact reduce the amount of energy required to do the surgical procedure,” Dr. Nixon told Ocular Surgery News.

The current standard for grading cataracts, the Lens Opacities Classification System III, yields results that are subject to interpretation. There is no accepted means of using objective data on cataract density to determine the amount of energy required to remove a cataract, Dr. Nixon said in the study.

Donald R. Nixon

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Dr. Nixon developed the Pentacam Nucleus Grading System (PNS) to work with the Pentacam Scheimpflug imaging system (Oculus) to generate objective and reproducible cataract density readings and used these to preset phaco parameters and evaluate the outcomes.

The results were published in the Journal of Cataract and Refractive Surgery.

Patients and parameters

The prospective study included 400 cataract patients who underwent Scheimpflug imaging with PNS. Patients who required complex cataract surgery were excluded.

The patients were assigned to two groups of 200. Patients in the first group underwent cataract surgery and IOL implantation based on preoperative evaluation, with no adjustment to phaco settings. These patients had a mean age of 71.7 years. The second group underwent cataract surgery with settings adjusted preoperatively based on objective cataract grades. These patients had a mean age of 74.4 years.

The second group was divided into three subgroups based on PNS cataract grading: grade 1, grades 2 to 3 and grades 4 to 5.

In the grades 2 to 3 subgroup, only the surgeon’s standard settings were used. In the grade 1 subgroup, the standard power setting was decreased by 50% and the standard duty cycle power by 20%. In the grades 4 to 5 subgroup, the standard power setting was increased by 100% and the standard duty cycle power was increased by 20%.

All patients underwent phacoemulsification with the WhiteStar Sovereign platform (Abbott Medical Optics). Effective phaco time, balanced salt solution use and needle time were measured for each subgroup and compared with baseline values for the first group.

Reduced phaco time and energy

PNS measurements showed that in the first group, 36 patients had grade 1 cataracts, 137 patients had grade 2 to 3 cataracts and 27 patients had grade 4 to 5 cataracts. In the second group, 38 patients had grade 1 cataracts, 128 patients had grade 2 to 3 cataracts and 34 patients had grade 4 to 5 cataracts. The distribution of cataract grade was similar between groups.

Effective phaco time and balanced salt solution used were statistically significantly lower in the second group than in the first group for PNS grade 1 and grade 4 to 5 cataracts.

Needle time was significantly less in the second group for grade 4 to 5 cataracts. There were no statistically significant differences between the groups for grade 2 to 3 cataracts because standard settings were used in those eyes, and results were not reported, Dr. Nixon said.

Ongoing safety enhancements

Reducing phaco power and fluid infusion will minimize the potential for damage to the corneal endothelium and blood-aqueous barrier, Dr. Nixon said.

“Phaco energy, both mechanical and cavitational, leads to turbulence, acoustic energy and free radical generation, creating forces that extend far beyond the tip of the needle,” he said. “Fluid flow, both the total volume as well as material in it, such as lens particles and air bubbles, creates further stress on the anterior chamber structures.”

Further studies that have looked at newer energy dispersion technologies, such as the Ellips handpiece with transversal ultrasound (AMO), perform with different cataract grades and have shown an improvement in relative phaco efficiency compared to longitudinal phaco alone, Dr. Nixon said.

“I don’t want this study to stop here,” he said. “Each company has advanced newer fluidic and power options, with Alcon’s OZil Intelligent Phaco, B+L Stellaris with dual linear control and wave modulation, and AMO with Ellips II and Fusion Fluidics. I’d like further work to be done looking at linking the concept of preoperatively grading and then objectively looking at these new enhancements, in terms of optimizing efficiency and minimizing energy dispersion, and how we may be able to assist ourselves and our colleagues in utilizing these new technologies most effectively in individual types of cataract grades.” – by Matt Hasson

Reference:

• Nixon DR. Preoperative cataract grading by Scheimpflug imaging and effect on operative fluidics and phacoemulsification energy. J Cataract Refract Surg. 2010;36(2):242-246.

• Donald R. Nixon, MD, FRCSC, DABO, can be reached at Trimed Eye Center, 190 Cundles Road, East Suite 100C, Barrie, Ontario L4M 4S5, Canada; e-mail: trimedeyedoc@rogers.com.
• Disclosure: Dr. Nixon is a consultant for Oculus, Abbott Medical Optics, Allergan and Novartis.