OASC | SURGERY

Femtosecond Lasers and the Correction of Astigmatism During Cataract Surgery

Improved precision benefits doctors and patients.

By Susan Worley, Contributing Editor

Cataract surgery, currently the most frequently performed ophthalmic procedure in the U.S. and around the world, is projected to become still more common as the population ages.¹ Also increasingly common will be the desire on the part of patients to have longstanding visual problems, such as astigmatism, addressed at the time of cataract surgery. Many patients will choose to pursue refractive procedures even though Medicare and most forms of private insurance don’t cover their costs.

More recently, femtosecond lasers, which a growing number of experts believe can improve safety, accuracy and clinical outcomes associated with cataract surgery, have brought with them additional financial and clinical considerations. Here we examine femtosecond technology, including its use to correct astigmatism during cataract surgery, and some challenges associated with incorporating the use of these lasers in clinical practice. This article assumes that decisions to use this technology must be made jointly by patients and clinicians, after careful discussion of all relevant financial and clinical considerations.

Figure 1. Real-time OCT imaging assists surgeons in creating incisions with extreme precision.

The Arrival of Femtosecond Lasers

The use of femtosecond lasers for cataract surgery emerged far more recently than many patients and other non-clinicians believe. While this technology was first introduced in 2001, it was initially approved only as a technique for creating lamellar flaps during LASIK surgery. It wasn’t until 2009 that the U.S. FDA approved the use of the first femtosecond laser for capsulorhexis, lens fragmentation or liquefaction, and corneal and arcuate incisions. Since that time, three other femto lasers have become available in the U.S. (Table 1)

As various indications for these instruments were approved in stages, many ophthalmic surgeons who were initially impressed by femtosecond laser capabilities during LASIK surgery were eager to try the technology for new indications. Enthusiasm over this technology continues to grow, although it’s estimated that fewer than 10% of all cataract surgeries today are performed with femtosecond lasers, and that fewer than 20% of all U.S. cataract surgeons have regular access to these lasers.

“Since femtosecond lasers were first introduced for flap creation during LASIK,” says Cathleen M. McCabe, MD, of The Eye Associates in Bradenton, Fla., “the technology has steadily improved. These machines are faster and much more precise than they were originally. But even back in 2001, when I first observed a femtosecond laser being used for flap creation, I remember being impressed. I remember thinking that this was a very elegant and precise way of cleaving tissue plains in the cornea.”

Douglas D. Koch, MD, professor of ophthalmology at the Cullen Eye Institute, Baylor College of Medicine in Houston says that he also initially used the femtosecond laser to make flaps during LASIK procedures.

“It took about 3 or 4 months before I realized how superior the use of the laser was in terms of predictability and safety,” says Dr. Koch. “Within 6 months, we actually abandoned use of the steel microkeratome, and stopped offering it as an option, except in very rare situations when femto wasn’t an option.”

Over time, as the FDA further validated the safety and efficacy of femtosecond laser use for a broader range of applications, Dr. Koch was among the many cataract surgeons who were encouraged to try the machine for new procedures.

“When this technology was brought into the realm of cataract surgery, I was excited,” Dr. Koch says, “because I was already familiar with the many potential benefits of the laser, and I believed the key factor that was going to make the laser work for cataract surgery was going to be the imaging. Imaging isn’t a major issue when femtosecond lasers are used for LASIK, but it’s a critical factor for cataract surgery. It’s necessary to have a 3-D model of the cornea and the anterior segment of the eye to perform surgeries safely. That is where the manufacturers have done such an amazing job in bringing us this technology for cataract surgery — in melding the precision of the femtosecond laser with the superb imaging capabilities of OCT, or confocal microscopy.”

Greater Confidence During Planning

While experienced cataract surgeons may be exceptionally proficient when planning the steps for manual cataract surgery, femtosecond lasers provide surgeons with a greater degree of confidence that their surgical plan will be executed with precision.

“When you make a plan for a surgical procedure with a femtosecond laser, you’re absolutely sure that the laser is going to do what you want it to do,” says Dr. McCabe. “For example, during the capsulorhexis step, we typically strive to make the opening very consistent in size and shape, as close as possible to an absolute circle, and with precise centration.”

As cataract surgeons have learned from Warren Hill, MD, says Dr. McCabe, the effective lens position — where the intraocular lens implant ultimately sits in the eye — is affected by the size, centration and circularity of the capsulorhexis.

“If a surgeon chooses to make the opening 5.0 mm, which happens to be what I choose, this can be done with absolute precision and certainty using a femtosecond laser. If I attempt to do this manually, I’m limited by just how precise my estimation of 5.0 mm is, and I can get very close to creating a circle, but the difference is between trying to draw a circle versus allowing a computer to accomplish it.”

To further assist surgeons in pre-operative planning, software programs — either integrated or available in optional, product-specific equipment — enable input of high-resolution digital images of the eye, kerotometry and other biometry. This information in turn allows surgeons to carefully plan LRIs and other astigmatism corrections, and make real-time adjustments, such as changes in the location of incisions, during surgery.

“My laser allows me to program my personal preferences for arcuate incisions, the specific patient’s anatomical dimensions, and other diagnostic data into the laser treatment plan, which then helps me tailor an efficient procedure to the patient, to support achieving the best possible visual outcomes,” says Mitchell A. Jackson, MD, founder and CEO, Jacksoneye, Lake Villa, Ill.

Addressing Astigmatism With the Laser

As with manual procedures, each surgeon tends to adopt a unique approach to addressing astigmatism with the femtosecond laser.

“In general,” says Uday Devgan, MD, private practice at Devgan Eye Surgery, chief of ophthalmology at the Olive View UCLA Medical Center and clinical professor of ophthalmology at the UCLA School of Medicine, “I believe that the femtosecond laser is best for treatment of 0.75 to 1.5 diopters of astigmatism only. More than 1.5 diopters of astigmatism is best treated with a toric lens implant, and toric IOLs are available to treat up to 4 diopters. Even with lower amounts of astigmatism, the toric IOLs tend to provide better results than the femtosecond laser.”

In some cases, experts opt to make incisions in lieu of using toric lenses, because the latter can be considerably more expensive than arcuate cuts. On other occasions, rather than deciding between the use of the laser and the use of a toric lens, some experts employ a combination of techniques, using the femtosecond laser to fine-tune results. Regardless of personal preferences, surgeons generally agree that incisions made with femtosecond lasers are more accurate.

“When I use femtosecond lasers I can be very accurate about two things: the length of each incision and the depth of each incision,” says Jeffrey Whitman, MD, of the Key-Whitman Eye Center in Dallas, Texas. “If you program X number of millimeters or degrees, the computer will do exactly what you program it to do, and it will perform it again and again. It’s also a great advantage to be able to use the OCT to look at the thickness of the cornea where you are making an incision. There are many debates about manual limbal relaxing incisions, and some surgeons won’t perform them because they assume that they won’t last. What many of us involved in radial keratometry realized years ago is that these incisions have to be deep. So you need to know what the depth of the limbal area is where you are going to make your incisions.”

Whitman says that guessing can create problems.

“If you make a 600-micron incision,” says Whitman, “and the depth is 850 microns, your incision won’t be very deep. On the other hand, if the depth is 550 microns, and you make a 600-micron incision, you’re going to have a hole in the eye, and you’re going to have to suture it. My femtosecond laser will give me the thickness at the middle part of my incision, and I can have it calculate 80% of that, so I can make my incisions deep, and I can know that I won’t have a perforation. I also know my incisions are deep enough that they can be expected to last. With manual incisions, we never had this capability. Many people make very shallow incisions and this doesn’t result in a long-lasting effect. With my femtosecond laser, I have more predictability and precision when I make incisions than I ever had before.”

Dr. Koch notes that although a good peer-reviewed study comparing manual blade incisions to those made by femtosecond laser has yet to be published, he believes there is a benefit to performing corneal relaxing incisions with the laser. He adds that in his own practice he uses the laser for astigmatism correction in three different ways.

“For some patients who require relatively low astigmatic corrections, I actually perform intrastromal relaxing incisions, which never penetrate the surface,” says Dr. Koch. “Patients have absolutely no discomfort, and there is no risk of dry eyes; it’s a wonderful approach. A second approach is to program the laser to make penetrating incisions, and then I determine whether to open these, either by using wavefront aberrometry intraoperatively, or by checking the patient postoperatively. If the patient, either on the operating room table or postoperatively, is undercorrected, then I can open the femtosecond laser incision to get a better benefit. That’s something I’ve just been exploring and liking.”

“A third way I use the laser is to make tiny little marks in the cornea — alignment marks for the toric IOL. I’ll make these toric marks at the intended meridian, and then I’ll use a device that makes a topography image, and with that, calculate the site of the lens implant, and in so doing, we can put the implant exactly where I plan it. I then look at the femto marks and I can compare them. They provide a marker that I can use postoperatively to check lens stability, and corroborate that the lens actually ended up where I expected it to.”

Patient Selection

Some cataract surgeons who use the femtosecond laser are unlikely to abandon the use of manual techniques entirely. Even some laser enthusiasts continue to perform certain cataract procedures manually. For example, some surgeons prefer not to make entry incisions with the laser, because they find these openings difficult to make or difficult to enter. Moreover, all surgeons continue to encounter patient situations in which they’ll choose not to use a laser at all.

“In every practice, there are some patients who for one reason or another are not good candidates for femtosecond laser,” says Dr. McCabe. “Use of the laser is always an out-of-pocket expense, for one thing, and some patients just can’t afford to pay the additional fees. In addition, traditional cataract surgery is sometimes the better choice when, for example, the anatomy of a patient’s eye or lack of cooperation on the part of the patient prohibits coupling of the eye to the laser. A patient who can’t lay prone won’t be able to fit underneath a laser. And of course, there are some well-known contraindications to the use of a laser, and to the use of incisions to correct astigmatism.”

An excellent review of femtosecond lasers by Zoltan Nagy, MD, published in Clinical Ophthalmology in 2014, provides an overview of contraindications to use of the laser, with an emphasis on the small non-dilating pupil, as well as approaches to challenging surgical cases.

Dr. Devgan notes that for some cases of irregular astigmatism, incisional approaches should be avoided, whether with laser or with manual techniques. Pathologies such as keratoconus, pellucid marginal degeneration and corneal scars are among those that should be considered for a traditional, manual procedure.

Deciding Whether to Purchase

To date, the hefty price tags for femtosecond lasers, which range from approximately $300,000 to $500,000, have perhaps been the greatest obstacle to ownership. However, experts say another problem is anticipating the new developments that may be on the horizon for any given laser, and how quickly these might receive FDA approval. As Dr. McCabe puts it, “obviously you want to be able to do what you want to do with a laser when you’re purchasing it, without having to wait for critical applications to be approved.”

Albert Castillo of the Outpatient Ophthalmic Surgery Society (OOSS) says an ASC should carefully consider its patient base before purchasing a laser. Clinicians who aren’t ready to purchase may consider using a femtosecond laser at a nearby open-access ASC, or may consider leasing a laser.

“You need the volume to support acquiring a femtosecond laser,” says Mr. Castillo. “An ASC should have about 1000 surgical cases per month to support a new laser. For those which lack the volume to support the purchase of a laser, it’s possible to lease one instead. There are mobile units that can be made available to facilities for use, in exchange for a per-use fee.”

Dr. Whitman notes that surgeons should keep in mind that each of the currently available lasers has a unique set of features.

“I think it’s important for surgeons to know that just like excimer lasers, femtosecond lasers are not generic,” says Dr. Whitman. “For example, the way that beams actually fire in the laser, in terms of spot separation and energy, among other things, are different with each laser. Laser X is not the same as Laser Y or Z.”

Dr. Devgan, who has tested multiple lasers, strongly recommends that other surgeons do the same. He likens comparison-shopping for femtosecond lasers to that of shopping for automobiles. “The best way to decide which one you want is to try multiple models, and arrive at your own conclusions. Surgeons should do the same with femtosecond lasers — test drive before you buy.” ■

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