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Corneal inlays an effective option for presbyopia correction
One surgeon provides insight into his surgical technique for implantation of corneal inlays.
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Uncorrected presbyopia results in avoidable vision impairment, and as of 2005, more than 1 billion people globally were classified as presbyopic.
In the United States, 55% of the population wears vision correction, and of this segment of the population, 53% are prebyopic. The majority of these presbyopes wear spectacles for presbyopia correction.
Freedom from glasses is attractive to a subset of the presbyopic population and can be achieved in many ways. In addition to contact lenses, presbyopia correction may be surgically achieved using monovision LASIK or PRK, conductive keratoplasty, scleral spacing procedures or refractive lens exchange.
IntraCor (Technolas Perfect Vision), a new, non-U.S. Food and Drug Administration-approved procedure, involves the use of a femtosecond laser to reshape the interior of the cornea without any surface penetration. The use of presby-LASIK is another option; however, presby-LASIK is also not currently FDA-approved in the United States.
Yet another novel way to correct presbyopia is through the use of corneal inlays. The two corneal inlays currently undergoing FDA clinical trials are Raindrop (ReVision Optics) and Kamra (AcuFocus).
In this surgical maneuvers column, Minoru Tomita, MD, PhD, describes the surgical technique for, as well as his experience with, the use of corneal inlays to correct presbyopia.
Thomas “TJ” John, MDOSN Surgical Maneuvers Editor
Minoru Tomita
The Kamra corneal inlay is an effective option for the treatment of presbyopia. The device is made of polyvinylidene fluoride with nano particles of carbon. The ring has a central aperture of 1.6 mm, which increases depth of field and improves near and intermediate vision with minimal impact on distance vision. The inlay is currently available in Japan and approved in 48 other countries, and the final module of the product’s pre-market approval has been submitted to the FDA.
In East Asian countries such as Japan, the majority of the population is myopic. Furthermore, the prevalence of patients with high myopia is higher in Asia than in white, black and Hispanic populations.
In our clinic, more than 1 million patients have already been treated with LASIK surgery to correct their refractive error. To address these myopic and post-LASIK presbyopes, I developed the protocol for implanting the Kamra inlay post-LASIK surgery, either independent of the initial LASIK surgery, or as a planned two-step procedure. I have found that both approaches cause fewer dry eye symptoms and result in higher patient satisfaction than thick-flap procedures.
Patient evaluation
Post-LASIK Kamra procedures begin with careful patient evaluation. The patient must be evaluated for dry eye disease, and any symptoms should be treated aggressively. It is extremely important that the corneal surface is in good condition at the time of the surgery.
It is also important to perform optical coherence tomography imaging to confirm the original LASIK flap thickness. Surgeons should never rely on the planned or programmed flap thickness from the prior LASIK procedure.
To achieve the best range of vision, the patient’s postoperative refraction in the inlay eye should be −0.75 D. Post-LASIK Kamra patients experience an average myopic shift of −0.60 D, so I prefer for my patients to be between plano and −0.25 D at the time of inlay insertion. Any hyperopic refraction needs to be corrected prior to inlay implantation to ensure optimal outcomes.
Surgical technique
Patients who present with both ametropia and presbyopia should receive both the Kamra inlay and LASIK correction. The LASIK procedure is performed as usual with a 100-µm flap (Figure 1). Among these patients, the postoperative refractive target for the non-inlay eye should again be between plano and −0.25 D.
Whether performed separately or as a two-step procedure, the pocket interface must be created at least 100 µm below the original flap interface. In my practice, I create the pocket and insert the inlay a minimum of 1 month after the LASIK procedure. If necessary, an enhancement can be performed at the time of inlay implantation by lifting the original LASIK flap.
Figure 1. Perform a traditional thin-flap LASIK procedure at least 1 month prior to inlay implantation.
Images: Tomita M
To surgically implant the inlay, the surgeon first marks the ideal placement on the visual axis, usually between the first Purkinje image and the pupil center, in the nondominant eye. A corneal pocket is then created using a femtosecond laser with pocket software at a depth of 200 µm to 250 µm. The laser should be set to a 5 × 5 spot/line separation or smaller to achieve the smoothest resection possible with minimal energy.
It is important to note that in patients who have previously undergone corneal cross-linking and are now stable, the energy output of the laser should be increased when making the pocket interface. For the best result, the incision should be created temporally (Figure 2) between the previous LASIK flap edge and as close as possible to the limbus to minimize induction of astigmatism.
After careful dissection of the pocket (Figure 3), the inlay is loaded into the forceps and inserted into the pocket. The inlay is initially inserted slightly beyond the centration mark (Figure 4) and then carefully pulled into the desired position. This technique allows for better control of inlay placement.
When the inlay is in the desired position (Figure 5), the forceps are opened to release the inlay and slowly withdrawn from the pocket (Figure 6). Irrigation of the interface is not required or recommended. Minimal manipulation inside the pocket interface will reduce postoperative edema and allow the best results and fastest visual recovery (Figure 7).
Figure 2. Mark the prior flap edge and limbus. Ensure your pocket opening is between these two points.
Figure 3. Dissect the pocket. The pocket should be at least 100 µm below the prior flap interface.
Figure 4. Using a ring marker, mark the cornea to provide a guide for inlay placement.
Figure 5. Carefully insert the inlay. Pay special care to not introduce epithelial cells into the pocket.
Figure 6. Once you are satisfied with the inlay position, release the inlay and remove the forceps.
Figure 7. Inspect the inlay placement and recenter if necessary.
Follow-up care includes topical antibiotics five times per day for 1 week and steroids for at least 3 months, tapered down thereafter. I also encourage patients to practice reading without their glasses and to be sure to return for their regular postoperative checkups.
Conclusions
To date, nearly 3,000 post-LASIK presbyopic patients implanted with the Kamra in their nondominant eye at my surgical center have returned for their 1-year postoperative follow-up exam. Mean uncorrected near visual acuity was J6 at baseline and J2 at 1 year (P < .001), with a mean uncorrected distance visual acuity in the inlay of 20/16 at baseline and a mean of 20/20 at 1 year (P < .001). In subjective responses, 95% of patients were satisfied with their vision, and only 8% have needed reading glasses.
Based on our experience over the past 2 years, we have found the Kamra inlay to be a safe, effective treatment option for our patients with presbyopia and refractive errors. As a result, the inlay is our preferred treatment for presbyopia correction.