After decades of research, Kamra inlay offers cornea-based treatment for presbyopia
We now have our first FDA-approved intracorneal inlay for the surgical treatment of presbyopia, the AcuFocus Kamra inlay. I have been involved with research in the field of intracorneal lenses for the treatment of refractive errors for more than 30 years, and the journey to approval of the Kamra inlay is an enlightening example of the trials and tribulations of the innovation cycle.
My first introduction to intracorneal lenses for the treatment of refractive error was at Southend-on-Sea in England in the clinic of Mr. Peter Choyce. Choyce was implanting polysulfone inlays into the cornea for the treatment of high myopia, and I saw many patients with up to –15 D of myopia have quite excellent outcomes. Further investigation also revealed many failures, with vascularization of the cornea, corneal melts and extrusion. In reviewing the literature, I learned that Jose Barraquer, MD, himself had investigated synthetic corneal inlays for the treatment of aphakia, and many other researchers, including John Henderson, MD, the former chairman at Mayo Clinic, also made similar attempts with different materials.
Research by many others, including Perry Binder, MD, and Bernie McCarey, PhD, and myself confirmed that the corneal keratocytes and epithelium are primarily nourished by glucose diffusing through the endothelium from the aqueous in the anterior chamber. Anything that obstructs this diffusion eventually results in aseptic necrosis of the cornea. We learned that very small inlays placed very deeply in the cornea could survive, but the primary solution was to utilize a material that allowed diffusion of aqueous through the inlay, such as a hydrogel, or to micro-fenestrate impermeable materials.
Much trial-and-error research has led us to the three corneal inlays currently available in the world for the treatment of presbyopia. These include the Kamra inlay, which is implanted in a pocket and uses small-diameter aperture optics to increase depth of focus; the ReVision Optics Raindrop inlay, which creates a multifocal cornea by altering anterior corneal curvature when placed under a LASIK flap; and the Presbia Flexivue Microlens, which uses a higher refractive index hydrogel than the cornea and creates bifocal optics when placed deeply into the cornea in a pocket.
Earlier attempts by many to treat aphakia, myopia and hyperopia have been abandoned in the face of superior alternatives, including IOL implants and laser corneal refractive surgery. As we all know, lens implants and laser corneal refractive surgery can also treat presbyopia, but they are invasive and not ideal in their optical performance for all patients. The category of presbyopia most in need of a better optical solution is the early emmetropic presbyope between the ages of 45 years and 60 years with a clear lens and some residual accommodation. This includes the millions of baby boomers who have undergone corneal refractive surgery and are now presbyopic. Of course, monovision and so-called blended vision are a viable alternative, and all ophthalmologists are familiar with the advantages and disadvantages of this approach. I am a significant user of monovision and blended vision in my cataract and LASIK patients, but would prefer to have an option that retains good distance vision while enhancing intermediate and near vision. The intracorneal inlay is an attractive option.
I have served as a consultant for all three inlay companies at one time and am currently a consultant and board member for AcuFocus. Our practice is just now launching this option for our patients, and I have worked with this technology and the innovator and early-adopter surgeons around the world for nearly 15 years. So, a few thoughts and lessons learned for the surgeon interested in the Kamra inlay.
The Kamra inlay utilizes hyperfocality, the same optical principle employed in a high-quality disposable camera to allow a high-quality image from distance through intermediate to near. The eye is ideally set at mild myopia of –0.75 D and no astigmatism to generate the best outcome. This refraction gives good intermediate vision for many 45 to 60 year olds with some sacrifice at distance and, for the older patient, near. Distance vision is enhanced by the small-diameter aperture, just as in a camera with a low f-stop, and depth of focus is increased, improving near vision as well. In the camera literature, this is called hyperfocality. There is some measurable loss of brightness, especially in a mesopic environment, which is the reason the inlay is implanted in only one eye, preferably the nondominant eye. The implant works well through a range of plano to as much as –1.25 D, and mild astigmatism of less than 1 D is also well tolerated, but –0.75 D sphere is ideal.
It is apparent that few patients exist in the world with exactly –0.75 D sphere, so in the global experience, the most common patient is treated with a combination of LASIK or PRK with a Kamra inlay implanted 1 or more months later in a pocket at least 100 µm beneath the LASIK flap and never less than 200 µm from the surface. The ideal patient after surgery is therefore plano in the dominant eye and –0.75 D sphere in the nondominant eye, although good outcomes are usually obtained in patients between plano and –1.25 D in the eye to be implanted, with improvement in both distance and near in the low myope. Even though labeled for use between +0.5 D and –0.75 D, patients with any level of hyperopia are less satisfied.
LASIK is contraindicated after an inlay has been placed if a femtosecond laser is used to create a flap because experience has shown the inlay will be damaged. While the indication is off label in the U.S., global experience confirms that the patient with prior LASIK does well with a Kamra inlay, and PRK on the surface can be performed as an enhancement over an inlay. Centration of the inlay is critical, and use of the AcuFocus AcuTarget HD helps predict the ideal location. This device also screens for dry eye and measures the eye’s depth of focus, which is a good educational tool for the patient. A healthy ocular surface is critical, and while quite well tolerated, a mild interface reaction between the inlay and cornea is a normal part of wound healing. This is best mitigated by an extended course of topical steroids and copious lubrication.
Patients with measurable dry eye should be treated before surgery to normalize the ocular surface. I use the same indication I use for LASIK and PRK: an absence of corneal staining with lissamine green. My steroid regimen includes a drop four times daily for 1 month, three times daily the second month, twice daily the third month and then once daily the fourth month. I always place a punctal plug in the inferior puncta, usually a 3-month collagen plug. Omega-3 supplementation and Restasis (cyclosporine ophthalmic emulsion 0.05%, Allergan) are used routinely by some surgeons and electively by me. Topical lubricants are routine. Early evidence of a poorly controlled ocular surface includes a hyperopic shift on refraction and the so-called “red ring” on topography, suggesting desiccation over the inlay. If this is seen, aggressive treatment with a potent topical steroid and dry eye therapy is indicated.
In rare cases in which the hyperopic shift and topographic change do not respond to medical therapy, it is best to promptly remove the Kamra inlay. If good visual outcomes are not obtained in the face of a healthy ocular surface, the most likely causes are poor centration or a less-than-ideal base refraction. Poor centration can be diagnosed with the AcuTarget HD and the impact of residual refractive error with a careful refraction. Both can be remedied with an enhancement treatment. The inlay can be recentered surgically under topical anesthesia as an office-based procedure, and residual refractive error can be treated with PRK.
After any surgical intervention, a medical regimen similar to that recommended for the primary procedure is wise. In patients with a well-centered inlay, appropriate refractive error and a proper postoperative medical regimen, patient satisfaction is very high. The procedure can be performed in an office surgical suite, and I do mine under the Visx excimer laser microscope (Abbott Medical Optics) in our laser suite. Careful sterile technique is recommended, and a short course of antibiotic similar to that used in LASIK or PRK is recommended. A bandage contact lens and NSAID therapy is not needed, although I place one drop of NSAID on the eye before placement of the suction ring when making the pocket, which seems to enhance intraoperative and early postoperative comfort. I have counseled my patients to not expect significant improvement in vision until 1 month, but if a “dry technique” is used, avoiding any irrigation in the pocket with secondary corneal edema, vision on day 1 can be quite good.
In my small series of patients to date, vision at distance, intermediate and near has been 20/25 or better in all patients on day 1 with a greater “wow” effect than I had anticipated. All diagnostic tests and retinal examinations can be performed through and around the inlay with a dilated pupil. Retinal photocoagulation, vitrectomy and even epiretinal membrane surgery have been performed with a Kamra inlay in place outside the U.S. with good outcomes. Cataract surgery has also been performed, and with a monofocal aspheric IOL implanted, patients recover good vision through a range from far to near. A small-diameter aperture IOL is in the early phases of clinical trials outside the U.S., and visual outcomes to date have been nothing short of remarkable.
For me, the approval of the AcuFocus corneal inlay is the culmination of decades of research and development dating back to Jose Barraquer himself. Careful surgeon training is critical and available from AcuFocus. My patients and I are pleased to have this option available.
Disclosure: Lindstrom reports he is a consultant and board member for AcuFocus.