September 02, 2021
3 min read
September 02, 2021
3 min read
Click here to read the Cover Story, “With resurgence of LASIK, debate reemerges on femto vs. mechanical microkeratomes.”
I use the Ziemer CrystalLine femtosecond laser system to make my LASIK flaps because I think femto is the safest and most effective way to make those flaps.
When I first started in practice, the previous owner I worked with used a mechanical microkeratome, and I remember seeing how inconsistent it was in regards to flap thickness and diameter depending on the shape of the patient’s cornea. There seemed to be a lot of nuance and a steep learning curve required to determine exactly the best way to optimize it for different patients.
The biggest advantage of the femtosecond laser is consistency. Regardless of the shape of the cornea, the femtosecond laser makes a perfect flap with uniform thickness from the edge to the center of the flap almost every time. This results in a much lower incidence of free caps, partial flaps, buttonholes and epithelial defects. Because of the smoothness of the bed, there is also some evidence, at least empirically, to suggest a lower rate of late flap dislocation for femto flaps compared with microkeratomes.
Because it is more precise, the femtosecond laser also allows you to make consistently thinner flaps. I routinely make 90-µm flaps for my LASIK procedures. By doing that, you can conserve a lot more tissue than you could with a microkeratome. The flap centration is also adjustable after suction with some femtosecond lasers, which helps ensure ablation on the visual axis.
That is not to say that the femtosecond laser is without complications. I have had a small handful of buttonholes and free caps, but the chances of that happening overall are much rarer. The other complications specific to the femtosecond laser are related to the energy used to create the flap, including transient light syndrome, opaque bubble layer and anterior chamber bubbles. Fortunately, most of these are nuisances that resolve quickly and are not the kinds of complications that affect the patient’s ultimate visual outcome. Moreover, we used to think that the incidence of diffuse lamellar keratitis was maybe higher with femto, but the lower energy settings available today make this less likely. Of course, the femtosecond laser is an added cost, but if it were my eyes or my family’s eyes, I would want the safest and most effective device that we have. I think that is the femtosecond laser.
Dagny Zhu, MD, is from NVISION Eye Centers in California.
I brought a Zeiss VisuMax femtosecond laser into my practice in 2014, and now, I use it for about 60% of my LASIK cases. However, a good mechanical microkeratome is still an important part of any refractive surgeon’s toolkit.
Surgeons in the United States have been persuaded to think that femto is overwhelmingly better by successful marketing efforts of the femto manufacturers. However, we have learned through tracking surgical outcomes that both technologies yield comparable results with extremely low risk of unanticipated events such as buttonhole. Before surgery, we tell patients that procedures using femto might be slightly more comfortable and a few seconds shorter, but the statistical results of both systems are equivalent. Consistency of flap thickness is much tighter with femto than microkeratome, and this is a factor in counseling those with thinner corneas. Having the microkeratome allows us to offer LASIK at two different price points. For folks who may be economically challenged, either because of young age or the pandemic, it is a good option to help them afford LASIK if we can go the microkeratome route.
We also use microkeratomes in certain situations in which it might not be possible to use femto, including steep corneas above the manufacturer’s recommended range for specific platforms. We had an incident recently in which the air conditioning in our laser room failed on the day of surgery and the temperature rose to a point above which the use of the VisuMax is permitted. Because we had the mechanical microkeratome on hand, we were able to switch and salvage surgery for patients on that day. We did not have to disappoint them and crater a fairly significant surgical lineup.
I think the learning curve for microkeratomes is steeper than for femto. I make these choices from a position of significant volume, as well as accumulated comfort and experience.
David Wallace, MD, is from LA Sight in Los Angeles.