How patient movement can interfere with femto laser-assisted cataract surgery

Unexpected head movement can lead to suction loss and displaced laser beam delivery despite safety mechanisms of the femto platform, allowing the femto-laser grid pattern to be delivered into the cornea. (Video courtesy of Sonia Yoo, MD)

Femtosecond laser-assisted cataract surgery (FLACS) is a latest advance in technology that is transforming traditional cataract surgery into a refractive procedure. Multiple studies have shown that laser-assisted cataract surgery can increase precision and reproducibility of the anterior capsulotomy, reduce effective phacoemulsion time, cause less postoperative inflammation to the anterior chamber, and possibly reduce surgically-induced endothelial cell damage.

Sonia Yoo, MD

However, it is discussed much less often that the safeguards built into FLACS instruments can fail and allow the femto laser grid pattern to be delivered into the cornea.

“We think this is what happened to one of my patients,” said Sonia Yoo, MD, professor of ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine. “Suction was lost during lens segmentation. The segmentation pattern that was intended for the lens nucleus unintentionally treated the cornea.”

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The good news is that the unintentional corneal scoring had no effect on the visual outcome, Dr. Yoo noted.

The patient had uncorrected 20/20 vision the day after surgery and still had 20/20 vision on her last exam a year after the incident. But because of the unexpected treatment of the patient’s cornea, she implanted a monofocal lens rather than the planned multifocal lens.

“The patient was quite happy with 20/20 vision,” Dr. Yoo said. “Even with the monofocal lens, her vision was so much better than it was pre-op that she was perfectly happy with the result. But this still points out that unexpected head movement can lead to suction loss and displaced laser beam delivery despite the safety mechanism of the femto platform. This is a potential development that you should discuss with your patient as part of your informed consent.”

Misplaced laser delivery

Suction was lost during lens segmentation. The segmentation pattern that was intended for the lens nucleus unintentionally treated the cornea. (Video courtesy of Sonia Yoo, MD)

Misplaced laser beam delivery is not a common occurrence. Dr. Yoo said she found just one similar event in literature, submitted by one of the session discussants, Samuel Masket, MD, Founding Partner of Advanced Vision Care and Clinical Professor of Ophthalmology at the Jules Stein Institute, David Geffen School of Medicine, University of California, Los Angeles. The common contributing factor to both events was patient movement. Dr. Yoo’s patient was moving so much she needed three attempts to dock and establish suction.

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Once suction was established on the third try, the femto platform safety mechanisms should have detected the subsequent loss of suction and blocked the laser pulse. Instead, it appears that the conjunctiva occluded the suction holes, which prevented the platform from detecting the loss of suction and allowing the laser to fire after the eye had moved and delivering the segmentation pattern to the cornea.

Fortunately, the patient had a healthy Bell’s response and the eye had rolled up and out as she began to blink. The laser treatment was limited to the inferior third of the cornea and there was no damage to the central cornea.

“I don’t know if applying the segmentation pattern to the central cornea would have made a difference in post-op vision, but I was relieved we didn’t have to find out,” Dr. Yoo said. “More than a year out, I can still see that grid pattern on her cornea, but there have been no visual sequelae. Dr. Masket said he had a very similar case except that the grid pattern on his patient’s cornea faded over time.”

Identifying difficulties

The incident reinforces the need to identify patients who might present difficulties for laser treatment that might not be as significant for traditional phaco. Patients with deep-set orbits or very small eyes could be present challenges to femto laser treatment.

Patients who are unable to hold still can also be problematic. Deeper sedation is not a viable option, Dr. Yoo said. Not only must patients be alert, responsive, and able to focus on a bright light as directed during the procedure, they must also be able to move themselves in and out of a lying position for the instrument used in this procedure.

It is also important to realize that laser safety mechanisms can fail. While the laser should not be able to fire once suction is broken, it is possible that the device can sense suction even after the eye has moved if tissues such as the conjunctiva somehow occlude the suction holes.

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Modifying the preoperative conversation and informed consent can be a useful strategy to deal with potential misadventures, she continued. The reality is that things do not always go as expected during any cataract surgery, not just FLACS. It particularly important to help the patient understand that surgical plans may change depending on how the procedure evolves. 

“It is important to your pre-op discussion with the patient to explain that while you intend to use a laser and to implant a multifocal lens, there may be unforeseen circumstances which preclude the use of either and may require the use a monofocal lens in the interest of safety,” she said. “Safety for the patient is our first concern.”