Corneal incisions: Art form or science?

Take-Home

Creating incisions during laser refractive cataract surgery achieves better visual outcomes for patients.

By Lynda Charters; Reviewed by Eric D. Donnenfeld, MD

New York-The effects of creating incisions during laser refractive cataract surgery are multifaceted.

For instance, they let surgeons achieve better visual outcomes for patients by reducing the variability resulting from factors such as patient age and corneal biomechanics. The effects of the incisions in reducing astigmatism postoperatively are titratable and eliminate overcorrection or flipping of the axis that occurred previously when the surgical effects could not be as precisely controlled.

Eric D. Donnenfeld, MD, discussed astigmatic keratotomy during laser refractive surgery and compared it with conventional astigmatic keratotomy.

“Astigmatic keratotomy is an extraordinarily important part of laser cataract surgery,” said Dr. Donnenfeld, a founding partner of Ophthalmic Consultants of Long Island and Connecticut, clinical professor ophthalmology, New York University Medical Center, New York, and a trustee of Dartmouth Medical School.

Astigmatism affects the visual acuity and becomes the rate-limiting factor in any patient’s visual outcomes after laser cataract surgery and causes glare, halos, and uncorrected visual acuity. Only about 25% of surgeons perform limbal-relaxing incisions (LRIs) during cataract surgery, while 70% of patients have cylinder of 0.5 D or more preoperatively, he said.

Art, science of incisions

LRIs have a number of advantages in that they are easy to perform, inexpensive, repeatable, done during cataract surgery, are associated with fast recovery, and do not preclude future excimer laser procedures.

However, LRIs can be variable with an unpredictable response because of the imprecise depth, length, angulation, and position of the incisions.

“LRIs are an art form and not a science,” Dr. Donnenfeld said.

“The advantage of laser refractive cataract surgery is that the incisions are now fully customizable and adjustable and they are no longer an art form,” he said. “They are a science. The laser can provide the exact size, placement, and depth of the incisions. The first part of the problem has been solved.”

However, the response still remains unpredictable despite use of femtosecond laser incisions because of patient age, corneal diameter/curvature, pachymetry, corneal biomechanics, and IOP, he noted.

The full effect of the incisions is only achieved when the incisions are opened manually. The response achieved is titratable based on the energy settings used, the line spot separation, and the incision angulation.

The starting laser nomogram (Donnenfeld Nomogram for LRIs) can be reduced by one-third for femtosecond laser incisions because the incisions are made on a 9-mm arc rather than at the limbus, he said.

Dr. Donnenfeld demonstrated the effects of the incisions created using a laser with a low energy setting (2.5 µJ and a spot separation of 5 μm).

“When high energy is used, the incisions significantly spread apart,” he said. “With a low energy setting of 2 µJ, the incisions could not be opened despite our best efforts. We found a happy medium by using 2.2 µJ with a spot separation of 5 μm. Using these settings, the incisions opened with slight difficulty. We can now titrate our results.”

Dr. Donnenfeld and colleagues conducted a study that included 38 patients who had a mean preoperative cylinder of 1.1 D. The mean cylinder decreased to a mean of 0.39 D when one incision was opened in each of the 38 patients.

“We determined that 18 patients did not require opening of the second incision,” he said. “We modulated the other 20 incisions by opening them partially or totally; the cylinder in these patients decreased to a mean of 0.31 D that remained stable at 1 month postoperatively.”

“For the first time, we have the ability to use a new technology that allows us to do something that cannot be done with manual astigmatic keratotomies,” he added.

Incisions can now be made at the time of cataract surgery, they can be left closed or opened partially, intraoperative aberrometry can be used, or the patient can be evaluated 1 day, 1 week, or even 1 month postoperatively, at which time the incisions can be adjusted to titrate the effect, Dr. Donnenfeld noted.

“For the first time, we can achieve excellent results or improve the results with astigmatic keratotomies that take into consideration the results that vary with factors such as patient age, sex, and corneal hysteresis,” he said. “This avoids overcorrection and flipping of the axis, and I believe this will be one of the major advantages of laser cataract surgery.”

fyi

Eric D. Donnenfeld, MD

E: ericdonnenfeld@gmail.com

Dr. Donnenfeld is a consultant to Abbott Medical Optics, Bausch + Lomb, LenSx, and WaveTec. This article is adapted from Dr. Donnenfeld’s presentation during Refractive Surgery 2012 at the annual meeting of the American Academy of Ophthalmology.