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A surgeon with clinical experience with three femtosecond lasers discusses the practicalities of creating ideal femtosecond laser inlay pockets.
Reviewed by Majid Moshirfar, MD
Salt Lake City-Using a femtosecond laser to create the proper pocket in the correct position to allow the precise placement of a small-aperture corneal inlay (Kamra, AcuFocus) for optimal vision correction requires finesse and expertise.
“We have three different platforms that can create pockets for the inlay and they can all do an excellent job in experienced hands,” said Majid Moshirfar, MD.
“I personally use the Intralase iFS and the Alcon FS200 to create pockets and I can’t find a difference between them in performance,” said Dr. Moshirfar, clinical professor of ophthalmology, University of Utah Moran Eye Center and medical research director, Hoopes Vision, Salt Lake City.
But the Intralase iFS, Alcon FS200 and Ziemer FEMTO LDV Z8 are not identical. The iFS was the first femtosecond laser on the U.S. market, Dr. Moshirfar said.
U.S. surgeons have more experience on the iFS than any other platform and have devoted more time and attention to tweaking and calibrating its operational parameters.
“The limitation with this device is that it can only create a pocket along the temporal aspect of the cornea,” he added. “That can be a limitation when you have a patient who could be better treated with an incision from another direction.”
The FS200 and the Z8 have their own advantages and limitations. Both can create pockets at any angle.
The Z8 creates wider pockets than the other two platforms, which gives more space for instrumentation and maneuvering while placing the inlay. Docking is very easy and the device gives the familiar feel of microkeratome. The FS200 is quick and easy to operate and allows the operator to trace the path of the incision for more precise placement.
One notable pearl for surgeons is to create a pocket that penetrates at least 40% of the cornea depth.
“LASIK flaps today are around 100 to 120 μm,” he explained. “For a corneal inlay, a pocket as deep as 225, 250, or even 300 μm is advantageous for placement. The deeper you go, as long as you respect the stromal bed of 250 μm, the more you reduce the risk of hyperopic shift, visual fluctuations and dry eye symptoms in patients.”
Dr. Moshirfar offered five additional tips for successful corneal pocket creation and pinhole-aperture vision correction:
Patient selection is vital. Good surgical candidates are in good health, Dr. Moshirfar said, with no underlying disease.
Good surgical candidates also have a small angle kappa, the distance between the center of the pupil and the Purkinje reflex. The smaller the angle kappa, the more likely the patient is to see significant vision improvement. Patients whose angle kappa is 500 μm or larger are not good candidates for Kamra vision correction.
Patients should also have minimal refractive error before surgery and little to no astigmatism. Patients with significant refractive error may need LASIK or PRK correction before the inlay pocket is created. Patients with significant astigmatism must have it corrected before inlay surgery.
“You have to talk with your patients about expectations,” Dr. Moshirfar continued. “Pinhole-aperture technology can allow most patients to attain good near vision, but it won’t make everyone a J1. If you look at the FDA approval study, more than 87% of patients were 20/40 or better for near vision and 31% were 20/20 or better for near vision at the end of the 60 months study period. We cannot promise all patient that they will become 20/20 at near after surgery.”
Proper centration of the inlay is also crucial. In an ideal world, the center of the pupil would be coaxial with the four Purkinje images. In the real world, surgeons must assess the eye preoperatively.
If distance from the center of the pupil and the Purkinje reflex is less than 300 μm, Dr. Moshirfar advised centering the device on the Purkinje.
If the distance is more than 300 μm, he advised centering the device between the center of the pupil and the Purkinje reflex. Patients with a larger gap are not good candidates for the device.
Using a microscope
He also advised using a surgical microscope for optimal device placement. Current femtolaser platforms lack a microscope, which has prompted many surgeons to use the microscope on an excimer laser to implant the device. A conventional surgical microscope provides better visualization and more precise movement when inserting and placing the inlay.
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The final tip is to decenter the suction ring slightly in the direction of the incision. Decentering the ring to visualize a small bit of conjunctiva makes it easier to open the incision closer to the limbus. The closer the incision is to the limbus, the lower the risk of astigmatism and the less likely the pocket is to interfere with any later surgery.
Majid Moshirfar, MD
This article was adapted from Dr. Moshirfar’s presentation at the 2016 meeting of the American Society of Cataract and Refractive Surgery. He did not indicate any proprietary interest in the subject matter.