In the beginning, the specs for the Kamra corneal inlay read as follows:
“The Kamra inlay is indicated for intrastromal corneal implantation to improve near vision by extending the depth of focus in the nondominant eye of phakic, presbyopic patients between the ages of 45 and 60 years old who have cycloplegic refractive spherical equivalent of +0.50 diopters (D) to -0.75 D with less than or equal to 0.75 D of refractive cylinder, who do not require glasses or contact lenses for clear distance vision, and who require near correction of +1.00 D to +2.50 D of reading add.”1
It is safe to say that in the 2.5 years since the Kamra (AcuFocus) was approved, refractive surgeons have found ways to expand patient selection.
The same holds true with the cornea-reshaping Raindrop (ReVision Optics), which was approved in June 2016. Its manifest refractive spherical equivalent is slightly more hyperopic than the Kamra’s and it is not placed as deeply as the Kamra; all other specifications are generally the same. At the time of approval, it wasn’t known how the eye would react if either inlay were combined with other procedures, be that procedure an existing one or one to come. So, both came with warnings about combination procedures.2
The warnings didn’t stop surgeons from thinking about how to incorporate procedures such as refractive or cataract surgery.
“When new procedures or devices such as Kamra become available, it becomes the task of those surgeons who elect to involve themselves in the new technology to study and determine how to best use it to create safe, successful outcomes,” writes Martin Fox, MD, in this issue’s Visionaries and Educators (page 9). “Determination of which patients represent the best candidates for surgery … discovering how to handle pre-operative factors as well as making necessary adjustments in surgical techniques will be required to assure excellent and predictable outcomes.”
While corneal inlays are approved for emmetropic presbyopia, how the eye becomes that way, be it congenital or “acquired”, is not clearly defined. Waring et al. found that the Kamra inlay could be implanted in conjunction with LASIK, by correcting low levels of ametropia first, followed by corneal pocket creation and inlay implantation a week to a month later.3 Generally, this would be considered an “off-label” use.2
Others are looking off-label, too.
Shamik Bafna, MD, has stopped waiting for the perfect corneal inlay candidate to walk through his office door. Dr. Bafna, of the Cleveland Eye Clinic, has implanted about 250 Kamra inlays and 15 Raindrops using LASIK to tailor his results, creating the ideal scenario to implant a corneal inlay. His goal is to make the dominant eye emmetropic and the nondominant eye between -0.75 D and -1.00 D for the Kamra; between +0.50 D and +0.75 D for the Raindrop.
In Oklahoma City, Luke Rebenitsch, MD, has performed most of his 220 inlay procedures on the same day as the patients’ laser vision correction. His target post-LASIK refractions for both inlays are the same as Dr. Bafna’s, and with the inlay in place, his patients generally see 20/25 monocularly, at distance and near. He has also implanted them in spherical monofocal pseudophakes.
MEETING A NEED
In the United States, those between 45 and 64 years of age are projected to reach 83.9 million people in 2020.4 In combination with LASIK or cataract surgery, corneal inlays may satisfy the near vision needs of many presbyopes. A U.S-based, prevalence of refractive error study showed that only 25% of presbyopes were previously emmetropic.5 These people have had excellent distance acuity their entire lives but now require corrective lenses for reading and computer use, and they don’t like it.
Besides similar specifications the two inlays have other similarities. A femtosecond laser is used to make a pocket incision (a flap in the case of the Raindrop) in the corneal stroma at the appropriate implant depth. Proper centration is essential for optimal results. A key advantage to corneal inlays alone over laser vision correction or inlays and laser vision correction is that the devices are additive, meaning that no corneal tissue is removed during the procedure.6 Additionally, should the patient be unable to adapt, the devices can be removed and the cornea will, in principle, return to normal.
DIFFERENCES
The Kamra functions on the optics of a pinhole camera, increasing the patient’s depth of focus. The disc has a black background to blend in with the appearance of the pupil; it contains 8,400 microperforations to allow oxygen and nutrients to travel across the inlay.1 To aid in Purkinje image identification for centration of the Kamra, as well as tear film assessment, depth of focus and light scatter, Visiometrics offers the HD Analyzer.1 Initial concerns with respect to the black annulus impeding examination of the anterior and posterior chambers have been debunked.
John Vukich, MD, a medical monitor for Kamra’s phase 2 and 3 trials, says the inlay is 3 mm anterior to the pupil aperture, so it is easy to look around, even more so with anterior segment OCT, thus delayed diagnosis of pathology is not an issue.
Concerns, complications, contraindications
Dry eye disease is of particular concern for inlays because a poor tear film directly affects the quality of the vision postoperatively. Drs. Bafna and Rebenitsch, and virtually all refractive specialists, say that any ocular surface disease must be treated first. Both prescribe Xiidra (Shire) or Restasis (Allergan) pre- and postoperatively, when indicated. For Dr. Rebenitsch, that is about 30% of the time. Both also use 90-day dissolvable punctal plugs on all inlay patients, to aid in postoperative lubrication.
Ocular contraindications to corneal inlays include keratoconus, corneal dystrophies, herpes keratitis or zoster and other infections or inflammation. Patients with systemic diseases such as diabetes, autoimmune diseases and poor wound healing are also not good candidates.
Complications following implantation are minimal but the most substantial are fluctuations in vision and dry eyes, which may be treated with cyclosporine, in the case of aqueous deficiency, or LipiFlow (J&J Vision) if there is meibomian gland dysfunction. Other issues include haloes, glare and foreign body sensation. Should postoperative haze be a concern, it can be mitigated with the use of mitomycin C (MMC) during implantation.1 To prevent stromal haze, Dr. Vukich and Martin Fox, MD (see his sidebar) recommend a four-to six-week, slow tapered course of corticosteroids postoperatively. Endothelial cell density loss occurs initially but stabilizes after 9 to 12 months.2,3 There may be a possible shift in the refraction as a result of the inlay being a space occupying device.
REFERENCES
- Moarefi MA, Bafna S, Wiley W. A review of presbyopia treatment with corneal inlays. Ophthalmol Ther. 2017;6:55-65.
- Kamra inlay professional use information. https://www.accessdata.fda.gov/cdrh_docs/pdf12/p120023d.pdf .
- Raindrop near vision inlay professional use information. https://www.accessdata.fda.gov/cdrh_docs/pdf15/P150034c.pdf .
The Raindrop inlay has the same refractive index as the cornea and no actual refractive power, but it biomechanically displaces the button of corneal stroma overlying it anteriorly, increasing its radius of curvature.2 This alters the central refraction, increasing the patient’s ability to focus at near.
The Kamra is indicated for those with slightly myopic refractions.7 According to Dr. Vukich, “The pinhole effect of the Kamra flattens the defocus curve, therefore it negates a small amount of distance correction, in the order of -0.50D, improving distance acuity, while extending the near depth of focus.”
Moarefi et al. found the Raindrop is best suited for those with low levels of hyperopia, +0.50 D, with no prior refractive surgery procedures.6
What perfect patient profile?
By Steven W. Stetson, MD
It is rare that presbyopic patients have the perfect refraction — slightly hyperopic — as specified by FDA approval for the Raindrop Near Vision Inlay (ReVision Optics). Many presbyopes have worn glasses or contact lenses; many others have had successful laser vision correction procedures.
Maybe 20% of presbyopic patients who walk through my door fit that description. For them, whose minimal astigmatism has a spherical equivalent of roughly +1.00 MR, all that’s required is flap creation and implantation of a corneal inlay. However, paltry figures like 20% aren’t sufficient to build a presbyopic inlay practice.
I knew that if I wanted to expand my refractive surgery business, I’d have to expand the description. So I embraced the concept of performing simultaneous refractive surgery on virgin eyes and LASIK eyes, with a goal of achieving the optimal refractive endpoint for a corneal inlay to perform well. I apply this technique for both the Raindrop and the Kamra.
SURGICAL TECHNIQUE
In a virgin eye based on the current parameters for implanting the Raindrop, I create an 8.5-mm diameter flap around 160 microns with ideally 30% corneal thickness. In a patient who has had previous LASIK, I make a smaller diameter flap, between 7.2 to 7.6 mm that is deeper — around 180 mm — to stay a sufficient distance from the previous LASIK flap — ideally 40 mm minimum.
My technique for previous LASIK patients is mindful of the previous flap incision. In about half of patients, it is unknown where the original hinge is or the resulting thickness. Usually, the previous flap edges can be discerned; care must be used to stay well inside this edge when creating the new femtosecond flap, even if this means slightly decentering the new flap. I stay away from the previous LASIK flap because blade flaps tend to dive in from the periphery at a steep angle into the corneal tissue, and so the mid-peripheral LASIK flap is relatively thick. I strive to create a 40-mm “buffer” from any previous flap. I use optical coherence tomography (Spectralis; Heidelberg) to roughly determine where the original flap is located, and it is important to determine whether there is a nasal flap hinge or a superior flap hinge. Also, in patients with central corneal thickness above 600 mm, I obtain endothelial cell counts with a confocal microscope (CS4 Confocal Microscope; NIDEK) to confirm healthy endothelium.
Finally, successful dissection of the new flap trumps flap centration. For example, if the original LASIK flap is 1 mm or more temporalized than it ought to be, I ensure that the new flap is slightly temporal as well. Because if it is too central, I will be too close to the nasal mid-peripheral deep area of the previous LASIK flap. Fortunately, most old flaps are large diameter flaps, so I can easily stay well inside of them.
I take care to dissect at the level of the femtosecond hinge first, and I stay in the midsection with the dissector tool (Seibel Flap Lifter/Retreatment Spatula; IntraLase), applying force outward from center toward the periphery. This allows the proper deeper plane to propagate outward rather than chancing incorporating the previous more superficial LASIK plane.
I have had a 90% success rate with lifting the flap of previous LASIK patents, and only one case where I could not lift the new flap. In that case, I aborted the procedure and later implanted the Kamra inlay. The patient was fine with this choice as we had discussed this possibility prior to the procedure. The patient was told we could encounter issues with the LASIK flap that could require postponement. So, I have since reduced my flap diameter to 7.5 mm or less, and all post-LASIK procedures with the Raindrop have been successful. I have not observed any delays in healing or other complications.
By developing a specific surgical technique formulated to offer a corneal inlay to patients in this demographic, I have expanded the patient population for corneal inlay implantation and now have more options to offer presbyopes.
Steven W. Stetson, MD, is medical director at Diamond Vision in Manhattan. He has implanted more than 100 corneal inlays.
WHYS AND WHEREFORES
Dr. Rebenitsch has preferred the Kamra because patients “heal quickly with functional distance and near vision typically within a week.” For patients with light irises, he chooses the Raindrop, as it offers better cosmesis than the Kamra. “The Raindrop historically caused more haze because it is implanted at a shallower depth, at one-third of the corneal thickness, but using mitomycin C greatly reduced the incidence of haze.”
To manage patient expectations, Dr. Vukich focuses on diminishing the patient’s dependence on glasses, not removing the need for them completely. Dr. Vukich measures success in terms of acquiring J3 or 20/40 near acuity, which is sufficient for reading a cell phone or menu with no reduction in binocular distance acuity.
As for the Kamra, Dr. Rebenitsch places the inlay at about 250 microns from the endothelium. Dr. Bafna suggests that the pocket depth can go further, up to 300 microns, from the corneal endothelium. “The keratocytes are less active, deeper in the cornea,” Dr. Bafna explains, “allowing for faster wound healing, less inflammation and less postoperative haze.”
Dr. Bafna prefers corneal inlays to monovision for multiple reasons. First, the patient doesn’t have to sacrifice distance vision or stereopsis. Second, there is no need to pursue further accommodative changes. “Accommodation is dynamic and later in life, monovision will only correct intermediate vision, at best. Corneal inlays will continue to work effectively as the patient ages.”
As these patients develop cataracts, the inlay could be removed and a multifocal IOL implanted or the surgeon could implant a spherical monofocal or toric IOL, keeping the inlay in place, as long as a small myopic correction for the Kamra or hyperopic correction for the Raindrop is targeted.
CONCLUSION
Phase 1 and 2 studies are underway looking at eye drops, such as Novartis’ EV06, that might enhance reading vision without the need for eyewear; however, the patient would still need to instill the drop daily.7
Industry wants to find a permanent solution to presbyopia that doesn’t involve spectacles, contact lenses or drops. Corneal inlays may be the answer, offering adequate near vision while maintaining distance vision with the benefit of very few complications.8
“Corneal inlays are the most complex refractive procedure that I do,” says Dr. Rebenitsch, “but they offer high patient satisfaction.” OM
Kamra, deep in the pocket
By Martin Fox, MD, FACS
In general, we see three categories of potential KAMRA candidates: the emmetropic presbyope, the ametropic presbyope (hyperopic and myopic) and the post-LASIK patient. Each will require individualized counseling and approach both in terms of surgical technique as well as postop management.
The emmetropic presbyope represents the most clear-cut of all Kamra patients. Surgery consists of creating a femtosecond laser pocket at a minimum depth of 250 microns. I typically place these patients on broad-spectrum antibiotic and 1% prednisolone acetate drops for one week. After the first week we will adjust postop steroids to fluorometholone 1% drops, which are taken 4x daily for two weeks with reduction to twice daily for weeks three and weeks four. Progress is followed with vision testing and serial AcuTarget HD testing for ocular scatter index and tear film OSI mean readings, with adjustments made in therapy as indicated. Pocket cases have the speediest recovery for both distance and reading acuity.
Post-LASIK Kamra patients are approached in much the same way as pocket cases. Attention needs to be placed on the pre-operative AcuTarget HD measurement of OSI. Some patients may have had laser enhancement treatments that can have an additive deleterious effect on corneal light scatter and transmission. Again, those with readings of above 2.5 should be carefully counseled on the impact this finding can have on the final visual outcome, especially in the distance.
Hyperopia of over +0.25 diopters must also be addressed with surface ablation aimed at a -0.50 outcome. In anticipation of with-the-rule cylinder outcomes generated by the pocket side cut, we will do standard excimer treatments that incorporate a -0.75 cylindrical component at axis 180 degrees. In my experience, distance acuity outcomes improve significantly with this approach. Surface treatments are followed by mitomycin 0.02% application for 10 seconds. Postoperative drops follow the standard prednisolone acetate antibiotic regimen for one week adjusted to a fluorometholone taper over the next four weeks. We have noted a rare tendency of PRK Kamra procedures to develop pocket haze at the two-month postop period. Vigilance is therefore advised with such patients.
Patients with both distance and reading issues can be approached with combined or staged LASIK/PRK Kamra procedures. Because myopic ablations are centered over the line of sight, such treatments can at times result in prolonged healing and visual recovery. For this reason, individuals with 2 diopters (SE) or less we will offer PRK with simultaneous Kamra. This approach will eliminate the flap interface component as part of the healing response. For those candidates with prescriptions above -2.00, we will use a staged approach with LASIK (targeting the nondominant eye for -0.50) followed by Kamra insertion one month later. A standard excimer ablation for the nondominant eye is selected that incorporates -0.75 diopters of horizontal cylinder correction, again in anticipation of the with-the-rule cylinder often created by the relaxing effect of the pocket side cut.
Hyperopic presbyopes represent excellent candidates for simultaneous combined LASIK and Kamra inlay implantation. Excimer ablation treatments are not coincident to the central line of sight and hence do not have as significant an impact on visual recovery. We have treated individuals with up 3 diopters of hyperopia with excellent results. Those with higher degrees of hyperopia may be best counseled to consider clear lens exchange surgery as an alternative to Kamra.
REFERENCES
- Kamra inlay professional use information. https://tinyurl.com/yczmzu2h
- Raindrop near vision inlay professional use information. https://tinyurl.com/yb8egb7k
- Huseynova T, Kanamori T, Waring GO, Tomita M. Small-aperture corneal inlay in presbyopic patients with prior phakic intraocular lens implantation surgery: 3-month results. Clinical ophthalmology (Auckland, N.Z.)7(default):1683-1686.
- Colby SL, Ortman JM. Projections of the Size and Composition of the U.S. Population: 2014 to 2060. March 2015. https://tinyurl.com/ohxe279
- Vitale S, Ellwein L, Cotch MF, et al. Prevalence of Refractive Error in the United States, 1999-2004. Arch Ophthalmol. 2008;126:1111-1119.
- Moarefi MA, Wiley WF. Kamra: A review. Ophthalmol Mgmt. 2017;10:31.
- ReVision Optics Inc. A clinical trial to evaluate the safety and effectiveness of the raindrop near vision inlay for pseudophakic subjects. ClinicalTrials.gov . Updated July 10, 2017. https://tinyurl.com/y7z2vsdk
- Arlt EM, Krall EM, Moussa S, et al. Implantable inlay devices for presbyopia: the evidence to date. Clin Ophthalmol. 2015;9:129-137.
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