Microincision, small-incision coaxial phaco similarly safe, effective for hard cataracts

Continuous ultrasound energy, however, yielded greater corneal edema and endothelial cell loss than the pulse and burst energy modes, study shows.

Man Soo Kim

Microincision and small-incision coaxial phacoemulsification with varied ultrasound energy settings were demonstrated to be safe in treating hard cataracts, a study found.

However, ultrasound power mode had a significant impact on postoperative corneal thickness and endothelial cell density, the study authors said.

“Before our study, most surgeons thought that coaxial microincision cataract surgery may cause more corneal endothelial cell loss than conventional small-incision surgery in very hard cataracts,” Man Soo Kim, MD, the corresponding author, said in an email interview. “However, phacoemulsification using microincisions may be as safe and effective as the conventional small incision for hard cataract in our study. Especially with the pulse or burst modes, the intraoperative energy used and ocular damage were less than with the continuous mode in hard cataracts.”

Additionally, incision size clearly influenced the degree of surgically induced astigmatism, the authors said.

The study was published in the Journal of Cataract and Refractive Surgery.

Patients and parameters

The prospective, randomized clinical trial included 180 eyes of 135 patients. All patients had nuclear cataract hardness exceeding nuclear opalescence 5 on the Lens Opacities Classification System III scale.

“Because there are so many reports about safety in MICS with mild to moderate cataract, we wanted to investigate if MICS is as safe as the conventional incision in very hard cataract,” Dr. Kim said.

Additional inclusion criteria were a dilated pupil of 7 mm or greater and corneal endothelial cell count greater than 2,000 cells/mm².

Eyes with previous intraocular surgery and ocular comorbidities such as diabetic retinopathy, glaucoma, age-related macular degeneration and uveitis were excluded.

Eyes were randomized to undergo phacoemulsification through 1.8-, 2.2- or 2.75-mm incisions; each incision group included 60 eyes. Eyes in each group were further randomized into subgroups to have treatment with burst, pulse or continuous ultrasound energy. Each subgroup included 20 eyes.

Between-group differences in age, preoperative corrected distance visual acuity, endothelial cell density, central corneal thickness and peripheral corneal thickness were insignificant.

“Age should be similar among [incision] groups because human corneal endothelial cells respond to age-related increases in oxidative nuclear DNA damage by forming DNA damage repair foci,” Dr. Kim said. “Older persons can have smaller corneal endothelial cells that decrease more after surgery than younger persons.”

In the 1.8-mm incision group, phacoemulsification was performed with the Stellaris platform (Bausch + Lomb), which generates conventional ultrasound. In the 2.2-mm and 2.75-mm incision groups, surgery was performed with the Intrepid Infiniti platform (Alcon), which uses torsional ultrasound.

The Visante 1000 anterior segment optical coherence tomography platform (Carl Zeiss Meditec) was used to measure central corneal thickness and main incision thickness.

Results and findings

Study results showed that eyes in the 2.75-mm incision group had more surgically induced astigmatism at 2 months and less incisional corneal edema at 1 week than the 1.8-mm and 2.2-mm incision groups; these differences were statistically significant (P < .05).

Dr. Kim cited an earlier cadaver study showing that corneal relaxing incisions induced corneal astigmatism ranging from 0.58 D with a single clock-hour incision to 5.93 D with a unilateral 3-clock-hour incision.

“So, if the incision becomes larger, postsurgical astigmatism should be larger,” he said.

The three incision groups had statistically comparable ultrasound time, cumulative dissipated energy, corrected distance visual acuity, central corneal thickness and endothelial cell loss at 2 months.

Ultrasound time, cumulative dissipated energy, incisional corneal thickness and central corneal thickness at 1 week and endothelial cell loss at 2 months were significantly higher in the continuous ultrasound group than in the pulse and burst energy groups (P < .05).

Mean endothelial cell loss was significantly higher in the continuous power group than in the pulse energy or burst energy groups at 2 months (P < .05).

“The pulse mode delivers power at fixed power-off intervals,” he said. “The [length] of the power-on and power-off cycle is determined by the pulse frequency, which can be set on the control panel. In the burst mode, however, power is released at a fixed level, whereas the length of the power-off interval shortens as the foot pedal is depressed. In linear continuous mode, when the foot pedal is in position 3, power is released without a resting interval. So, we could chop the hard nucleus efficiently and there was less damage because of the off period in pulse or burst mode. But in continuous mode, there is no off mode. So, there can be more damage to the corneal endothelium in the same phaco time.”

Outcomes did not account for vacuum and fluidic settings, Dr. Kim said. – by Matt Hasson

Reference:

• Kim EC, Byun YS, Kim MS. Microincision versus small-incision coaxial cataract surgery using different power modes for hard nuclear cataract. J Cataract Refract Surg. 2011;37(10):1799-1805.

• Man Soo Kim, MD, can be reached at Department of Ophthalmology, Seoul St.Mary’s Hospital, #505 Ban-po Dong, Seocho-Ku, Seoul 137-040 Korea; email: mskim@catholic.ac.kr.
• Disclosure: Dr. Kim has no relevant financial disclosures.

It is amazing how cataract surgery continues to advance. As Dr. Kim and colleagues point out, with new phacoemulsification technology using pulse and burst modes, we can use less energy, and even for hard cataracts we can work through very small incisions. Endothelial damage was high in these dense cataracts, suggesting that we still need to be able to develop better techniques and equipment for this group of patients.

– David R. Hardten, MD
OSN Cornea/External Disease Section Editor
Disclosure: Dr. Hardten has no relevant financial disclosures.