What's new and old with microkeratomes?

Microkeratomes have come a long way since they first appeared in the clinic in the early 1980s. The still evolving technology has seen significant improvements in both the safety and predictability of procedures involving these instruments. EuroTimes spoke to Perry S Binder MD about the early days of the technology, the current state-of-the-art and the outlook for the future.

Q: Tell us a bit about the early days. What was the first microkeratome you used?

A: The first microkeratome I used was the Steinway instrument that Jose Barraquer helped develop in 1977 in Bogota. I did my first clinical case in 1980. That particular microkeratome was archaic, like a 1903 Ford. There was difficulty getting the microkeratome into the dovetail rings, and there were problems getting it to translate across the cornea. We would get stuck half way through. Suction was bad too. You would lose suction and would end up with all kinds of poorly shaped caps. Flap thickness predictability was also poor.

There wasn't any modification of the microkeratome until the BKS microkeratome (Barraquer-Krumeich-Swinger) developed and sold by Allergan in the mid 1980s. That technology came and went in about two years. In fact they were giving the units away for free by 1987. The next modification that I worked with was the Chiron Automated Corneal Shaper (ACS). That was a modification by Dr Jim Rowsey and Dr Luis Ruiz to allow better suction and more automatic translation through a series of gears across the eye. That machine has been subsequently modified by Lasersight and others to encase the gears so they don't get caught in the lashes. That machine is currently available. I've performed a couple thousand eyes with the ACS. It continues to have one advantage today in that it can make a thin flap. So if you ever really need a thin flap, the ACS is one to consider. The disadvantage is that it is old technology and there is a risk of buttonholes.

Q: What other microkeratomes have you tried?

A: I used the SCMD in 1993. Then I worked with the Eye Technology MLK unit in 1995. I used the Phoenix Keratec Universal Keratome in 1996. Then Alcon and Jorg Krumeich came out with the SKBM machine, which I started using in 1997. I have used the SKBM in some 3,000 procedures. Most recently I have been working with the Moria automated M2 in a small number of cases.

Q: There are so many microkeratomes on the market. What criteria should a surgeon use when choosing one?

A: The criteria one is looking for in a microkeratome today or any tool for the creation of corneal flaps are safety and predictability of flap dimensions. Those are the two key issues. All of the other bells and whistles that go along with microkeratomes are secondary to those primary concerns. <Any doctor looking at purchasing a new microkeratome has to ask how predictable the cap dimensions are.> Very few microkeratome companies are providing that information.
The current microkeratome technologies are good. Each machine has certain advantages and disadvantages. (insert PPT Graph comparing SKBM, Hansatome, Moria and the Amadeus). The SKBM has the advantage of seeing the cap being resected as it happens. The SKBM and the Innovotome are the only units that allows you to do that. The risk of buttonhole is decreased with the SKBM because you are aplanating the cornea first, then cutting. All the other machines applanate and cut simultaneously.

Q: What are the advantages of manual VS automatic translation?

A: There really isn't a big difference as long as you are experienced. The problem with manual translation is that you get more variation in flap thickness primarily based on the speed of translation across the cornea. The faster you move, the thinner the flap. If you are an expert, you can come close to partial prediction of flap thicknesses. The disadvantage is that your translation is never the same, even from case to case and within each case itself. That will affect the thickness of the flap dimensions. I personally believe that automatic is much better than manual. We only use automatic units in our clinic.

The trend is towards using automatic systems. More and more surgeons are entering the field and the younger inexperienced guy doesn't want to have to worry about the more difficult technical aspects.

Q: How do you integrate microkeratome technology into a large, high volume practice?

A: We have three doctors here. We have three SKBM machines. We haven't had problems integrating our practice because we all happen to like the SKBM. That gives us a lot of latitude. We have multiple standard heads, for 160 flaps. We also have the hyperopic or H-head, so we can do larger diameter flaps, for the hyperopic and mixed astigmatism cases. We have a thin flap head so we can get thin flaps when we need to. Alcon is about to release a thin, hyperopic head so we will have that option as well. We use blades from two different companies. One company's blade cuts thinner than the other. So if I am in a situation where I need to modify flap thickness, instead of changing heads, I might just change the blade.

Q: What are your thoughts on reusable VS disposable components?

A: Everything is reusable in terms of the heads of the microkeratomes, and the rings. The blades are all disposable, one blade per two eyes. Sometimes we might use one blade for one eye. One obvious example would be if you see defects in the blade before you use it, you discard it. But you might also do a case when you do not like what you see. The flap might be too thick, for example. You could change to a different head to give a different thinner flap, or change to a different blade to give you a thinner flap. Or you might see defects in the first flap, such as irregularities at the edge, or maybe you don't like the quality of the stromal surface.

I'll give you a good recent example. The patient had a relatively thin cornea, but it was flat. I needed to get a thin flap and a large diameter. We didn't have the thin hyperopic head yet. In the first eye, the diameter I needed was a 9 and I got an 8.7, so I had to change the ablation parameters for that particular eye to 6.5 x 8.5 instead of the planned 7 x 9, in order to correct the patient. What did I do for the second eye? I couldn't use the same head because I wouldn't get the same diameter. I switched to my hyperopic head to get a larger diameter. But that would give me too thick a flap so I changed blades to one that cuts 20 microns thinner. The second flap was 9.3 and I got a thinner flap as well. These are the kinds of things that surgeons need to look at to modify their particular results.

Q: Recent studies suggest that quality varies quite a bit from blade to blade. What do you do to maintain safety?

A: We have to ask ourselves why we get variations in flap thickness and why one company's blade cuts differently than another's. In 1981, I published the first paper on SEM and microkeratome blades and began to point out the defects that can occur with blades after one, two, four uses and so on. There is no doubt that there are differences in the way the blades are manufactured, in terms of sharpness, edge quality and angle of the edge. The position of the post versus the edge of the blade is also important. Some companies say they are modifying these factors to help predict what that blade is going to do. I personally inspect every blade myself and put the machine together myself. We don't let the technician do it. You have to have significant control over blade quality.

Q: We're seeing claims made for one or another microkeratome based on things such as chatter or striae creation. How can the various systems be compared?

A: How does one measure chatter? It is all subjective. How does one keep track of that? With a database.? I'm not aware of anyone in the world that has been able to do that. Similarly, how does one keep track of striae? There would have to be some clear definitions and cases would need to be stratified. We know that high myopes mostly have microstriae anyway.

What you can do is to compare flap dimensions. We will be presenting a white paper at the ASCRS in Philadelphia that does compare flap dimensions among microkeratomes. We have been comparing preoperative corneal thickness to created flap thickness. As corneas become thicker, with most microkeratomes you get a thicker flap. Conversely, the thinner the preoperative cornea, the thinner the flap. Our results indicate that one of the advantages of the SKBM is that it is insensitive to preoperative corneal thickness. This means you get more predictable flap thickness.

Q: What about some of the new technologies now entering the clinic?

A: There are two exciting new technologies, Waterjet and Intralase. I have done some electron microscopy evaluations on the Waterjet. It creates very smooth resections. The problem there is technically being able to accomplish this with relative ease without having too cumbersome a machine. This technology has been around for a few years, and it is still not being used clinically. This suggests that they are having difficulty accomplishing that goal. But it has promise.

The Intralase has generated a lot of interest and excitement. It has no blade and allows the surgeon to create diameters, hinge location and size by software control. What we want to start looking at is predictability. The company states that there is good predictability with small standard deviations, but they haven't published any data in peer reviewed journals. We will be getting an Intralase here in the next couple of months. There may be logistical problems in moving to an all-laser procedure. You would be creating the flap, then having to wait until the air bubbles dissipate, then bringing patient back and lifting the flap. Whether that has an impact on hydration factors, and predictability, only time will tell.

Microkeratomes do have an impact on visual outcome. The problem is we don't know how much. That is where Intralase may offer an advantage, if we can create more predictable flaps than a microkeratome. At present, using the SKBM, I have had no free flaps with 3000 eyes, and no buttonholes, with a standard deviation of +/- 13 microns. That is really good. We don't know if Intralase can do that or better. I would challenge the companies bringing out the new technologies to say here is what mine does, in this range of corneal thicknesses, in this range of corneal curvatures and so on. That is what the surgeon wants.

Q: Microkeratome phobia is sometimes considered a rationale for developing other technologies. Do you see this in your practice?

A: In our clinic, the fear factor is tied with finances in patients' decision making process to undergo surgery. I've not had one patient who is specifically microkeratome phobic. Patients don't say they want PRK over LASIK. It is usually the other way around. I tell patients that I've had seven buttonhole flaps, in 8,000 eyes, and that those occurred with a microkeratome that I'm not using anymore. This makes patients feel a lot better.

An interesting question in 2002 and beyond, when we start seeing Intralase in practices, and standard microkeratomes, is how do you script this for the patient? That will be a little more difficult. Even if there are no buttonholes, a blade is a blade. We won't know the level of microkeratome phobia until we start with the Intralase. I can say anecdotally that doctors who have switched over to Intralase have embraced it 100%. Within a month or two they are using Intralase totally. It may a psychological advantage to patients. Time will tell.

Dr Binder is a pioneer refractive surgeon and past president of CLAO and ISRS. He currently practices in the Gordon/Binder Vision Institute, La Jolla, California.