Successful Surgery With a Mechanical Microkeratome

Creating flaps: Let's compare apples to apples.

BY ROY RUBINFELD, M.D.

Having shifted from PRK to LASIK in 1996, I have used nearly a dozen microkeratomes, including the femtosecond laser microkeratome. The keratome I use almost exclusively now is the Moria One disposable (Antony, France). In my experience, I have found the Moria to be an extremely safe, reliable and consistent device for creating excellent flaps over thousands of procedures. As someone who became involved with excimer laser treatments in 1991, I am a rapid adopter of new technology when that technology is clearly better than what I am using. I have not found this to be the case with the femtosecond laser.

Making Unfair Comparisons

I believe that much of the discussion of whether to use a mechanical microkeratome or a laser microkeratome involves media and patient perception issues. There has been some clever marketing for femtosecond lasers using the word "bladeless," which sounds to many people as if there is no cutting involved. In fact, the truth is any femtosecond or mechanical microkeratome cuts corneal tissue in order to make a flap. I have heard it said that laser keratomes make flap complications impossible. Having treated a number of patients with such "impossible" complications during my career, including practicing corneal surgery for 20 years, has made me skeptical of such claims.

I also often hear comparisons between one femtosecond laser keratome and "the" mechanical microkeratome. There are quite a number of mechanical keratomes available and they are not all equal in their quality, design, flap characteristics, safety or consistency. Comparing the newest laser keratome with a mechanical keratome I became dissatisfied with in 1997 certainly would make the laser look "better." To be fair, in order to compare apples and apples, comparisons should be made between a high-quality modern microkeratome and a femtosecond one.

My rate of flap complications is extremely low and I believe the rates of such complications are roughly equal between modern, state-of-the art mechanical microkeratomes and laser microkeratomes. Finally, increased laser keratome costs get passed on to both the patient and the doctor. I do not believe that the current laser is worth the financial investment.

Approach to Surgery

My general approach to surgery involves preoperatively evaluating the patient carefully for signs of basement membrane dystrophy, which could be a problem with any microkeratome. These patients have a higher chance of having loose epithelium, diffuse lamellar keratitis (DLK) and ingrowth under the flap postoperatively.

Also, when we instill anesthetic drops preoperatively, we try to minimize the interval between the time the drops are administered and the time the flap is actually created. If you let the anesthetic drop sit on the eye, the epithelium can be loosened, reducing adhesion of the epithelium. When this happens, any microkeratome is more likely to produce a corneal abrasion.

I pay close attention to what size flap I'll want to make. Desired flap diameter depends on the anatomy of the patient's eye, what size laser ablation is planned and other factors. I generally prefer larger flaps for most patients. The advantage of this is that if you have a large ablation, you are applying the full ablation onto the stroma, not the epithelium. Because of its low enhancement rate and rapid visual recovery, I routinely use a laser with a large ablation pattern, the Allegretto (WaveLight Laser Technologie AG, Germany), for the vast majority of my procedures. It goes out to 9 mm so I usually make 9 mm to 10 mm flaps. This flap size can be achieved with the Moria by adjusting the ring, stop and head sizes, giving me a great deal of flexibility. Additionally, the Moria microkeratome can also be adapted for epi-LASIK surface ablation.

In deciding which procedure (LASIK or surface ablation) is most appropriate for a patient, corneal thickness must be taken into account, but topography is also very important. If the topography is judged to be adequate and the corneal thickness is such that enough stroma will be left behind, I will generally perform a LASIK procedure. If the topography looks nearly perfect, but there are subtle irregularities, I may choose to perform surface ablation after discussing it with the patient because, in this case, a surface procedure is safer.

Also important is the degree of refractive error. Even with the ~100 μm flaps I consistently make with the Moria, higher degrees of myopia may require ablation depths larger than I recommend. For these cases, I will consider epi-LASIK or even a phakic IOL such as the Visian ICL (STAAR Surgical, Monrovia, Calif.). I will also consider surface ablation for patient with basement membrane disease. Preoperative and postoperative keratometry readings factor into these decisions as well, because if the postoperative cornea is too flat or too steep, quality of vision may be reduced.

Figure 1. Good Exposure. The keratome's path is clear of the speculum or any other obstruction.

Femtosecond vs. Mechanical Microkeratome

I find that visual recovery with the Moria is actually faster than with some femtosecond keratomes. If you look at the common postoperative regimens for steroid drops with each of these devices, most doctors use more corticosteroid steroids after femtosecond flap creation because the laser causes more inflammation. More steroid use increases risks of glaucoma and cataract.

Studies exist supporting both sides of various issues with laser vs. mechanical microkeratomes, such as which is better in terms of spherical aberration, flap thickness and consistency and other such parameters, but many of these studies are conducted with financial support from the manufacturers. Again, you need to compare apples with apples.

Surgical Pearls

Basic surgical principles apply with any keratome (mechanical or laser). It is necessary to instruct the patient about what to expect before the surgery and reassure them intraoperatively. The surgeon must also ensure good exposure of the globe prior to creating the flap. One critical key to avoiding flap complications is to always look where you are going. If the speculum is going to get in the way or the suction ring is not positioned correctly, correct the problem before you make the flap (See Figures 1 and 2). Simply put, pay attention and think ahead.

Recutting a flap, whether with a laser or mechanical keratome is to be avoided in nearly all cases.¹ I have seen quite a number of serious complications from recutting that involved long-term vision loss, with both the femtosecond laser and mechanical microkeratomes. Even waiting years after the original flap was cut and trying to cut under the original flap with different settings will not ensure safe recutting. That's another situation when surface ablation is a good idea. If you cannot lift a flap, consider a surface procedure with intraoperative mitomycin C.

Figure 2. Poor Exposure. Note that the inferior aspect of the speculum is in the way of the keratome.

Regardless of the keratome you choose and contrary to what some patients may think, the laser and the microkeratome do not do all the work. A surgeon is still a surgeon and there is no autopilot on these machines. Laser vision correction surgery requires a careful, detail-oriented surgeon who keeps the patient's interests paramount and chooses the most appropriate procedures and technology for each individual. Our patients may come in asking for various medications or technologies they may have heard of but, as surgeons, it remains our responsibility to determine the most appropriate medical procedure and technology for each individual. OM

Reference

1. Roy S. Rubinfeld, M.D., et al. To lift or recut: Changing trends in LASIK enhancement. J Cataract Refract Surg. 2003;29:2306-2317.

Roy Rubinfeld, M.D., is in private practice at Washington Eye Physicians & Surgeons, Chevy Chase, Md. and is clinical associate professor of ophthalmology at Georgetown University Medical Center/Washington Hospital Center in Washington, DC. He has no financial ties to any product discussed in this article.