REFRACTIVE SURGERY

Custom-tailored LASIK

Learn why this surgeon dismissed all-laser LASIK early on and what changed his mind.

By Kerry K. Assil, M.D.

When the 10-kHz IntraLase femtosecond laser (Intralase Corp., Irvine, Calif.), was introduced, I was less than impressed. I conducted a side-by-side comparison with the Amadeus mechanical microkeratome (AMO, Santa Ana, Calif.), examining variables ranging from clinical outcomes and patient satisfaction to patient throughput and costs. When I found that the mechanical microkeratome outperformed the femtosecond laser, I abandoned the laser.

Over time, however, the laser has evolved and many of the pros and cons have shifted. When I compared the newer 60-kHz IntraLase femtosecond laser with the mechanical microkeratome in creating flaps, I found that it offered a range of benefits compared with the microkeratome, which led me to switch exclusively to the laser. In addition, patients always have preferred the concept of a bladeless procedure.

In this article, I'll share what I've learned about the 60-kHz femtosecond laser and give you some pointers on how to use it.

Weighing the Technology

Using infrared light, the IntraLase femtosecond laser beam passes through the tissue until it reaches a specified focal point in the stroma. The beam then creates thousands of microscopic bubbles of carbon dioxide and water vapor that are positioned to define a dissection plane. The interconnected bubbles coalesce to create a flap.

Here are some of the benefits of this technology:

■ Flaps. When you use the femtosecond laser to create flaps, the stromal bed and back surface of the flap are smoother, and margins are crisper and sharper, with a nearly square edge, for less risk of epithelial ingrowth. Depths also are more uniform and predictable, so we can make the flaps as thin as we would like them to be.

■ Centration. The laser isn't perfect, but we can center flaps more easily than with a mechanical microkeratome. After we grossly center the suction ring onto the eye, we can use the computer keypad to adjust on the proposed flap centration before actually creating the flap.

■ Efficiency. In our operating suite, we can place the femtosecond laser and the excimer laser side by side. When using the femtosecond laser, we no longer need to assemble the microkeratome and sterilize the instrument. The IntraLase suction ring is sterilely prepacked so you're not required to place a lid speculum onto the eye. Following flap creation, we can use solid lid speculums (rather than wire ones), which coupled with less eyelid manipulation, diminishes meibomian secretions, reducing the need to prep and drape the lids and lashes. With a streamlined surgical process, we can treat more patients in a given unit of time.

The femtosecond laser has two potential drawbacks:

1) Initial expense. Although the cost of obtaining the laser initially appears to be a disadvantage, the incremental per-procedure cost really isn't a barrier. Once we adopted the technology, we found that increased efficiency in the operating suite and greater patient acceptance, which stimulates practice growth, helped offset the initial investment.

2) Space considerations. If you have a very small LASIK room, placing the femtosecond laser and the excimer laser side by side might present a space challenge.

The 60-kHz femtosecond laser allows you to center flaps more easily than with a mechanical microkeratome.

Customized Flaps

The 60-kHz femtosecond laser allows us to create customized LASIK flaps, which we can't do with mechanical microkeratomes. We can place the hinge at any angle or in any quadrant of the cornea and precisely vary the diameter, the thickness and the shape of the flap.

Although LASIK is well understood to be significantly safer than chronic contact lens wear — with less risk of infection,¹ endothelial cell loss, chronic dry eye and allergies — we still want to make it as safe as possible. Customizing LASIK flaps and creating ultrathin flaps further reduces the risk for ectasia.

We also can use the femtosecond laser to create an oval flap, which is an advantage because the superficial cornea actually is oval, not circular. Oval flaps can be created equidistant from the limbus in all locations. A small benefit to this approach is a reduced risk of margin inflammation. The closer you get to the limbus — the most immunologically active part of the cornea — the more likely you are to trigger inflammatory reactions.

Maximizing the flap size by creating an oval flap allows more space for the hinge. We can house the hinge along the cornea's longer cord length and thereby provide an equally long cord length in both the horizontal and vertical directions for the ablation itself. It's best to place the hinge in the temporal quadrant of the cornea, the largest area. This enables us to perform wide-area ablations without the risk of ablating (or needing to cover) the hinge. In addition, combining temporal hinges and oval flaps reduces the risk of opaque bubble layers from the femtosecond laser because we can vent the ablation-produced gases closer to the limbus. Temporal hinges also reduce the risk of dry eye compared with superior hinges, where we cut the parasympathetic nerves to the cornea in both the nasal and temporal quadrants.²

We're conducting a prospective, randomized, match-paired, double-blind study with the 60-kHz femtosecond laser comparing customized vs. not fully customized flaps. This study is being monitored by an institutional review board. We're studying stromal bed exposure (the surface area available for ablation for any given size flap), the incidence and clinical significance of opaque bubble layers, as well as other variables, including dry eye symptoms.

Prepping the OR, the Patient

Because there's no need for autoclaving, sterility issues have become a much smaller concern, and patient prepping has been streamlined. We've stopped applying betadine to patients' lids and draping the lids and lashes. National surveys have found no increased propensity for infectious keratitis in the one-third of patients having IntraLase procedures compared with the two-thirds having LASIK with mechanical microkeratomes. With simplified prep, the disparity in cost between the 60-kHz femtosecond laser and the mechanical microkeratome is somewhat blunted.

To prep patients for LASIK with the 60-kHz femtosecond laser, we instill prophylactic antibiotic eye drops before surgery. When the patient is taken to the treatment room, we instill additional antibiotic eye drops along with anesthetic eye drops. We also ensure that the speculum is sterile and the speculum and presterilized suction ring are handled in a sterile fashion. Disposables for surgery are available in prepacks, which also streamline the process.

Reducing Inflammation

When beginning to use the 60-kHz femtosecond laser, ophthalmologists often want laser-created flaps to lift as easily as microkeratome-created flaps. Our installation team had the same desire, and our laser energies were cranked up to fairly high levels, starting out at 1.3 microjoules with a 9 × 9 micron spot line/separation, but patients had a bit more inflammation than those treated with the microkeratome. Consequently, I dialed down the energy significantly by going to a 7 × 7 micron spot/line separation, and one of my lasers is now set to 0.8 microjoules and the other at 0.7 microjoules. Inflammation is now similar to that with microkeratomes, and the early postoperative discomfort is as low as it ever was.

When you start with the femtosecond laser, don't be enamored by making flaps super quickly. Rather, choose a higher density spot/line separation and much lower energy levels. As we advance to increasingly faster femtosecond lasers, I believe making flaps will become less of an issue for ophthalmologists because faster lasers inherently perform at lower energy levels.

Marketing All-laser LASIK

Patients often perceive all-laser LASIK as a more precise and safer approach than cutting with a blade. As a result, they often embrace the technology more quickly than do physicians. Nearly one-third of U.S. LASIK procedures are now performed with the IntraLase.³ But according to a study⁴ by Mahdavi, published in 2005, 81% of patients chose to have an IntraLase procedure over a microkeratome procedure.

After we adopted the 60-kHz femtosecond laser, when I explained to patients that we would be performing the bladeless all-laser LASIK, they were visibly relieved. I'd performed several surgeries over the years, and when patients would ask about all-laser LASIK, I dismissed it, explaining that I obtained better results with the other microkeratomes. But when I saw the relief on my patients' faces recently, I realized a certain percentage of them who shopped us in the past but opted for other practices probably did so because we didn't use the bladeless procedure.

Emerging Applications

There are a number of other emerging applications for this platform. For example, creative surgeons, such as Roger F. Steinert, M.D., have started to use the 60-kHz femtosecond laser as a surgical platform rather than as a LASIK platform. Surgeons are beginning to use the laser to make side cuts for corneal transplant patients, demonstrating that when they use this approach, they'll have the opportunity to decrease the amount of induced astigmatism.

In addition, I've always been interested in doing intrastromal ablations, an interest that was born during my fellowship years when I used the nanosecond laser, a more crude version of the femtosecond laser. With this application, I was interested in performing cuts or ablations in the stroma to change the curvature of the cornea without using a flap, like an intrastromal PRK. I think this may become an inherent therapeutic tool someday for enhancements without having to revisit the flaps, especially on patients who've had many previous treatments or patients who are pseudophakic and need small revisions and, thus, don't need a LASIK procedure.

As we get smarter, we'll even be able to use it for certain applications in cataract surgery. During my fellowship, we learned we could soften the nucleus at the time of cataract surgery with the nanosecond laser, but the amount of energy required outweighed the benefits. As we become more sophisticated with these tools, we'll find they have additional applications in other aspects of eye surgery. Clever glaucoma and retina surgeons, pediatric ophthalmologists and other specialists eventually will learn to apply some of this technology to suit their needs. nMD