October 2012

 

REFRACTIVE SURGERY

 

Refractive editor's corner of the world

Assessing femto-assisted astigmatism


by Vanessa Caceres EyeWorld Contributing Writer

 

Kerry Solomon, M.D.

Astigmatism continues to take center stage for today's refractive cataract surgeon. Based on the data of Warren Hill, M.D., approximately 50% of today's cataract patients have at least 0.75 diopters of astigmatism. Clearly astigmatism must be dealt with if patients are going to achieve their best uncorrected vision following surgery.

While toric lenses have become the mainstay for larger degrees of astigmatism, limbal relaxing incisions (LRIs) are commonly used for astigmatism in the setting of presbyopia-correcting IOLs as well as for treating lower amounts of astigmatism. While effective, LRIs can be unpredictable due to the nature of the procedure.

Femtosecond lasers have the potential to improve the precision and perhaps accuracy for the treatment of corneal astigmatism. We are honored to learn from the experiences of Drs. Culbertson, Foster, Packer, and Talamo with several of the femtosecond technologies in this month's "Refractive corner of the world."

Kerry Solomon, M.D., refractive editor

 
Lens exchange surgery

Wavefront-guided refraction during cataract and refractive lens exchange surgery Source: Mark Packer, M.D.

Users praise advantages, cite need for better nomograms

Predictability and control: Those are two words you commonly hear when you ask surgeons about the advantages of using femtosecond lasers for astigmatism treatment. These same surgeons acknowledge that this is still an evolving technology that needs long-term results and better nomograms to assist during procedures.

"In general, the femtosecond laser has the potential to make incisions precisely in the position, depth, and angulation that is desirable. It's extremely predictable in terms of the depth of the incision and in the optic zone," said William W. Culbertson, M.D., professor of ophthalmology, and director, Cornea and Refractive Surgery Services, Bascom Palmer Eye Institute, Miller School of Medicine, University of Miami. "You can do this with more precision than you can with a blade." With a blade, the depth created is not as uniform as it will be when created by a laser, Dr. Culbertson added. EyeWorld spoke with surgeons experienced with the OptiMedica (Sunnyvale, Calif.), LensAR (Winter Park, Fla.), and LenSx (Alcon, Fort Worth, Texas) lasers to hear their thoughts on their respective models for use in astigmatic cataract patients.

OptiMedica experience

OptiMedica's Catalys laser system has been in the news recently with the U.S. FDA's approval of its corneal incisions. Jonathan H. Talamo, M.D., associate clinical professor of ophthalmology, Harvard Medical School, Boston, has worked with the company for 5 years to assist in the laser's design and has 3 years of experience with the OptiMedica laser, performing procedures in the Dominican Republic. He anticipates obtaining a model soon for treatment.

"When we proceed with the laser, the cuts we do should have finely positioned diameter, length, depth, and centration," he said. "The laser allows more reproducibility, and when you combine it with optical coherence tomography, you can tell the laser how deep to go in every spot."

That standardization of astigmatic incisions was also something discussed by Dr. Culbertson. Dr. Culbertson has 3 years of experience with the OptiMedica laser, performing procedures in the Dominican Republic. With the laser, surgeons can use the bevel direction to help stabilize the effect of the incisionssomething that you cannot standardize manually, Dr. Culbertson said. "You can make these titratableyou can make the incision but not open it all the way to the bottom so the residual adhesions can remain intact at a certain position and depth. For example, you can treat 3 diopters and make the incision, but it forms a path of least resistance so the incision doesn't spread open immediately. It's still attached so you can go back later and deepen it to get a greater effect. That's something you can't do with a blade." Drs. Culbertson and Talamo believe nomograms tailored to the femto technology will make astigmatic incisions even more effective. "The establishment of nomograms will be a bit difficult, but it can be done. We just need to get a large enough number of patients to use it," Dr. Culbertson said.

LensAR experience

LensAR's 510(k) submission for corneal incisions is currently being reviewed by the. FDA for its corneal incisions this year, said Mark Packer, M.D., clinical associate professor of ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland. Dr. Packer and other surgeons have used the laser abroad, including having recent experiences in Latin America. Dr. Packer expects the use of the laser for astigmatism treatment will offer some benefits. "The drive toward greater accuracy and predictability in the outcomes of our incisional surgery for astigmatism represents a tremendous benefit for our patients, who will be able to get the desired results with a single procedure," Dr. Packer said. "Ultimately, our abilities to titrate and enhance precise limbal relaxing incisions [LRIs] may prove superior to outcomes achieved with toric IOLs for most degrees of correction."

He described fundamental ways in which LRIs created with femtosecond lasers are different than blade-based LRIs.

First, the laser should make placement of the incisions easier. "Successfully placed LRIs reduce the patient's cylinder without an overcorrection or axis shift. Determining the exact location of the cylinder is often challenging," he said. Femtosecond technology seems to indicate a more precise manner for incisional correction of astigmatism, including high degrees of astigmatism in post-keratoplasty eyes, Dr. Packer said.

"Common sense suggests that automating the incisional technology and thus eliminating the variability in performance, which is an ineradicable attribute of manual incision construction, will lead to greater reproducibility and less variation in results," Dr. Packer said.

Placement of LRI incisions should also be more predictable with femto technology, Dr. Packer added. "The potential for laser LRIs includes the ability to place the photodisruptive cutting effect at precisely the right orientation and to make cuts of the correct length and depth to create the desired refractive effect."

LenSx experience

The diamond LRI blade is going the way of the old RK blades as they are replaced with something better. Gary Foster, M.D., Eye Center of Northern Colorado, Fort Collins, prefers to use the LenSx laser to address astigmatism in as many patients as possible.

"I prefer to use it on all my cataract patients with astigmatism, whether they choose a multifocal IOL, a toric, or standard monofocal with an LRI with a standard monofocal," said Dr. Foster, who has used the LenSx model for over a year in commercial use.

"I have a strong preference for the femtosecond laser over diamond bladed LRIs because it reduces so many of the possible variables that lead to inconsistent outcomes," he said.

He usually employs the laser for astigmatism within the 1 D rangefor patients with higher astigmatism, he will combine the LenSx with a toric IOL. When using the toric to correct higher degrees of astigmatism, he'll still create some of the femtosecond arcuate incisions available but not open them, just as other surgeons have described for other laser models. "I use the slit lamp later to titrate the results. At the slit lamp, I use a Sinskey hook and open up incisions a bit to get more refractive effect and fine-tune the patients' results," he said.

Dr. Foster believes use of this technology will improve as surgeons become more accurate with their alignment and marking to reduce parallax. He also thinks that the nomograms under evolution for use with the laser will help surgeons who are new to the technology. Some nomograms formed from collective wisdom are available on internet discussion lists, Dr. Foster said.

Editors' note: The physicians have financial interests with the laser manufacturers that they discuss in this article.

Contact information

Culbertson: 305-326-6364, wculbertson@med.miami.edu
Foster: 970-221-2222, gjlfos@aol.com
Packer: 541-687-2110, mpacker@finemd.com
Talamo: 781-890-4979, jht1@comcast.net

Related articles:

Evaluation of dry eye after femtosecond laser-assisted cataract surgery: a prospective study

Why not femto? by Faith A. Hayden EyeWorld Staff Writer

Ethics of femtosecond laser-assisted cataract surgery by Ellen Stodola EyeWorld Staff Writer

Review of Femtosecond laser-assisted compared to standard cataract surgery for removal of advanced cataracts

Can femtosecond lasers live up to the hype? by Michelle Dalton EyeWorld Contributing Writer

The femtosecond choice by Enette Ngoei EyeWorld Contributing Editor

The future of laser-assisted cataract surgery: Clinical results and patient flow

Assessing femto-assisted astigmatism Assessing femto-assisted astigmatism
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