January 2018

NEWS & OPINION

Presentation spotlight
Bad memories of flap complications


by Stefanie Petrou Binder, MD, EyeWorld Contributing Writer


A large corneal scar after microkeratome LASIK where the blade likely made a
disconnected double cut in the cornea

A LASIK buttonhole flap that had epithelial ingrowth through the buttonhole region

Flap stria emanating from the flap hinge area
Source: J. Bradley Randleman, MD

For surgeons who have switched to the femto laser, severe flap irregularities are a distant memory. For those using mechanical microkeratomes, flap crisis management is essential know-how

Microkeratome flap complications make a good case for adopting the femtosecond laser, according to J. Bradley Randleman, MD, professor of ophthalmology, Keck School of Medicine, University of Southern California (USC), and director of cornea and refractive surgery, USC Roski Eye Institute, Los Angeles, during a presentation he gave at the 2017 ASCRS•ASOA Symposium & Congress.
“While femtosecond flap creation has its own set of complications, microkeratome flap issues can be more urgent and still require our attention,” Dr. Randleman said. “I was a late adopter of the femtosecond laser for flap creation. The flap creation techniques and flap morphology and architecture were reasonable with mechanical microkeratomes, and I was comfortable using them. OCT studies showed us we were getting exactly what we were anticipating for our flaps. That said, some of the more significant complications you can get with microkeratomes are harder to manage than those you can get with femto flaps. You are not going to get a bisected flap or a true buttonhole with a femtosecond laser. Also, with most lasers, you can watch the flap creation process, which is an advantage. I have now moved exclusively to the femtosecond laser. It does not mean you can’t get complications with femtosecond flaps—you can and will—but I do think they are a little easier to manage.”

Free caps and buttonholes

Dr. Randleman discussed classic, microkeratome-related complications from different cases that he experienced in his practice, in particular the creation of a free cap. Microkeratomes are used to create a hinged corneal flap to expose the stromal bed for laser ablation. In eyes with small corneas or deep orbits, or when the microkeratome achieves poor suction, decentered ring placement, or has faulty blades, the flap can detach and thereby create a free-floating cap, which under certain circumstances can change the course of the surgery.
“A free cap is one of the things we are concerned about with mechanical devices,” Dr. Randleman explained. “When a free cap is created, the surgeon has to decide whether it is best to carry out the excimer laser ablation or abort. The most important thing is to find the cap. First and foremost, you want to make sure that you have the flap tissue and that you have a normal optical zone. The next treatment step is somewhat controversial. Although I would say that the majority of surgeons do feel comfortable going ahead and completing the laser ablation, once the free cap has been identified and is seen to have a normal thickness, surgeons prefer to abort if the stromal bed is irregular. In situations with difficult suction, some surgeons may opt to abort from the start. If the surgeon continues with ablation, the cap is replaced in position afterward, either with or without sutures. If the surgeon chooses to abort, the flap is replaced and allowed to heal. When you can’t find the cap, I would argue against laser ablation at that time. Performing an ablation without replacing a free cap can lead to dire outcomes and complications, such as severely decentered ablations with the development of irregular astigmatism. I would allow the cornea to heal and then possibly treat with PRK later if possible.”
Flap buttonholes are caused by an abnormal lamellar cut during the creation of the LASIK flap, in which there is a connection between the flap interface and the corneal surface. Although uncommon, they need to be identified to avoid creating an irregular corneal surface and further complicate visual outcomes for the patient due to a flap stromal bed contour mismatching, which is likely to result from proceeding with laser ablation in this scenario. Surgeons should be cautious in patients with steep corneal curvature preoperatively, previous ocular surgery, and targeted thin flap creation. Also, microkeratome-related risk factors can include the loss of suction, decrease of power in the microkeratome motor, or blade imperfections. If a buttonhole flap occurs, the case should be aborted without laser ablation; otherwise sever irregularity can result.

Mechanical trouble

Like any mechanical device, microkeratomes are susceptible to blockage and space constraints on the surface of the eye. Dr. Randleman described the unwelcome scenario of the microkeratome freezing in place after swiping across the cornea. “With mechanical devices, you have to be very conscious about every step of the process as it is happening. You can have a case with good suction and no free cap formation but find the device has stopped moving and will not go any further forward or backward,” he said.
Surgeons who find themselves in this situation should take action by removing suction and manually retracting the microkeratome blade. Investigating the morphology of the flap is important, which may either be incomplete or severed off, as well as the optical zone, which may be smaller than targeted at the start of treatment. Eyes presenting with a full optical zone are generally safe to undergo ablation, cautiously. Dr. Randleman advised against laser ablation with grossly incomplete flaps, however, to avoid inadvertent treatment of the undersurface of the flap or the possibility of certain stromal areas not being ablated, which could create irregular astigmatism and entail further, difficult refractive corrective measures.
Smaller orbits present a unique set of problems for the surgeon. “Surgeons sometimes have trouble getting the device in place,” Dr. Randleman. “You want to make sure you get good clearance and good fixation. What we sometimes see is the lid speculum positioned too close, relative to the end of the microkeratome pass, which can cause either a suction break or for the pass not to be where you anticipate it was going to be. This is going to give you a disrupted flap with a poor hinge or a free cap, something that you want to watch out for. The surgeon may opt at this point not to continue treatment with excimer laser, although I would ablate as long as the flap is intact and its morphology close to what I anticipated it would be. Otherwise, you haven’t done anything for the patient aside from creating a surface that needs to heal. If you decide to go back and lift this flap later, you are right back where you were on the operating table. There are arguments either way.”
Gaining the requisite clearance for good suction on the corneal surface is essential. Eyes with spatial limitations that, for example, do not allow the use of a lid speculum may have trouble achieving microkeratome suction. “It can be challenging to get clearance,” Dr. Randleman. “You have to get good suction, but not unlike femtosecond lasers, once you get fixation you should be OK. One thing from the surgeon/patient perspective is the battle between the lid speculum being wide enough open for the surgeon, but too wide and somewhat uncomfortable for the patient. From my perspective as the surgeon, when necessary, I would prefer the patient to have 30–45 seconds of discomfort and a good outcome, rather than have a relatively comfortable but terrible outcome. That has always been my bias.”
“I think refractive surgeons know about the complications they can have with microkeratomes, but we don’t talk about them as much anymore. However, many surgeons still use mechanical devices in their practices, so it is very important to be aware of these complications and how we can work around them,” Dr. Randleman said.

Editors’ note: Dr. Randleman has no financial interests related to his comments.

Contact information

Randleman: randlema@usc.edu

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