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Combination technique addresses ametropia and presbyopia
A surgeon explains how to perform LASIK with implantation of the Kamra inlay.
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Spectacle or contact lens independence with good uncorrected distance and near vision is an important visual goal for a subset of the population over the age of 40 years. Patients with an active lifestyle are often looking for optimal unaided vision to carry out their daily activities in an uncompromised manner. Thus, surgical correction of presbyopia and regaining accommodation may be considered the ultimate frontier in refractive surgery.
While this final destination in optimal presbyopia correction, without any induced visual setback, is yet to be reached, evolving techniques focus on three ocular sites: the cornea, lens and sclera. Techniques involving the cornea include monovision LASIK, PRK, presbyLASIK, conductive keratoplasty, corneal inlays and IntraCor (Bausch + Lomb Technolas). Lens-based procedures and scleral techniques, including anterior ciliary sclerotomy, are alternative approaches used to correct presbyopia.
Although monovision via LASIK or PRK may be functionally acceptable to some, it induces anisometropia along with decreased stereopsis and binocular acuity. On the other hand, while presbyopic LASIK (peripheral and central), which is undergoing clinical trials in the U.S., supports corneal multifocality, it may result in loss of best corrected visual acuity and compromised quality of vision. Utilizing radiofrequency, conductive keratoplasty, a U.S. Food and Drug Administration-approved procedure, causes collagen shrinkage that temporarily corrects hyperopia and also improves near vision. The two corneal inlays for presbyopia treatment under FDA clinical trials are the Kamra (AcuFocus) and the PresbyLens (ReVision Optics). Lastly, the IntraCor procedure, not FDA approved, utilizes intrastromal laser delivery to create a series of concentric rings that steepens a small central zone in the cornea without the need to create a flap as in LASIK, which provides the added magnifying power required for near vision, including reading. Thus, a variety of corneal techniques are being developed in an attempt to surgically correct presbyopia.
In the continued quest for presbyopia correction, Dr. Allamby in this column describes his technique of “combined LASIK Kamra.”
Thomas “TJ” John, MD
OSN Surgical Maneuvers Editor
David Allamby
Most patients who present for presbyopia correction also have some degree of ametropia that needs to be addressed. The Kamra corneal inlay has been combined with LASIK surgery in a procedure known as “combined LASIK Kamra,” or CLK. This one-step procedure is intended for the correction of both conditions at the same time. Studies are ongoing comparing CLK with a two-step staged approach in which an initial thin-flap LASIK is followed several weeks later by inlay insertion into a stromal pocket.
The CLK procedure begins with good patient selection. Before the procedure, corneal thickness must be considered. CLK requires a 200-µm flap, with at least 300 µm left in the corneal bed. This generally limits the correction to 5 D of myopia or 3 D of hyperopia. Patients should also have a good preoperative tear film to be considered for a CLK procedure. It is necessary to carefully inspect for any cataract formation because the presence of a small aperture can magnify the lack of central vision.
The procedure
Before the procedure begins, a scan is made of the eye with the AcuTarget device (AcuFocus), which provides a printout showing recommended inlay placement. After topical anesthetic is administered, the eyes are prepared and draped as for a LASIK procedure. I then compare what I see in the microscope to the printed AcuTarget scan, which shows inlay placement relative to the first Purkinje image.
Standard 100-µm flap LASIK is performed on the non-implanted eye. Then, the same procedure is performed on the Kamra-implanted eye but with a 200-µm flap. The flap is returned to position as the endnote to the LASIK portion of the surgery. I then check the first Purkinje image again, relift the flap, place the inlay into my best-guess position on the corneal bed and replace the flap. Once the flap is replaced, I can confirm the inlay position. If it needs to be adjusted, I lift the flap again without adding any moisture and use a spear sponge to adjust the inlay into the correct position on the corneal bed.
In one-third of my cases, I can get the placement of the inlay correct on the first try. In the majority of the remaining cases, I lift the flap and reposition it once without adding any additional fluid. Ensuring minimal manipulation of the flap and keeping it dry prevents swelling of the corneal flap, aiding recovery.
The first step of a CLK procedure is to perform a regular LASIK procedure under a 200-µm flap. After the LASIK procedure is complete, the flap is replaced. The next step is to load the inlay into the surgical forceps and then relift the flap to allow for implantation of the inlay.
Images: Allamby D
The Kamra inlay is placed on the stromal bed and centered over the first Purkinje image.
The flap is replaced, and inlay centration is confirmed.
Postoperative
On postoperative day 1, I assess the patient’s vision and perform another AcuTarget scan to confirm the position of the inlay. I repeat this check at the 1-week visit. There is some flexibility with the placement of the inlay; as long as it is placed within 300 µm of the center, vision is not affected. If significant decentration is seen at day 1, recentration may be performed. However, corneal swelling at day 1 makes the scan less accurate, so the 1-week scan is more reliable. If the inlay needs to be recentered, lift the flap and slide it along the bed as previously described. When performing a recentration, I find it useful to memorize the ideal location for the flap and look for some identifying marker on the corneal bed as a target for positioning the inlay.
Postoperatively, patients are prescribed antibiotics four times per day for 1 week, a strong steroid four times per day for 1 week, and then a milder steroid starting at four times per day and tapering over the course of 3 months.
Learning curve
Since I have started performing this procedure, I have learned that the femtosecond laser settings are very important. I use a Ziemer LDV femtosecond laser, which has an overlapping spot pattern that provides a very smooth corneal bed. With other femtosecond lasers, a 6 µm × 6 µm spot/line separation or smaller is recommended. The finer grid pattern results in fewer bridges and a cleaner separation, improving the results of the procedure.
There is a learning curve with all new techniques, and I find that after 10 to 20 inlay implantations, a surgeon is comfortable with the procedure. Agility with the procedure improves with practice. The CLK procedure provides experience repositioning and centering the inlay because it is an open-eye approach. However, early data suggest that the future for this small-aperture inlay will be through pocket insertion, including pocket emmetropic Kamra and post-LASIK Kamra, or for ametropes combined with thin-flap LASIK in a two-step approach.
The Kamra inlay is an investigational device in the United States and is limited by U.S. federal law to investigational use.