The KAMRA Manifesto
Martin L. Fox, MD, FACS
With the April 2015 FDA approval of the KAMRA Corneal Inlay (AcuFocus), U.S. Refractive surgeons were offered the opportunity to take advantage of the very first technology designed to surgically correct presbyopia with a corneal implanted device. KAMRA is a biocompatible disk measuring 3.8 mm in diameter with a 1.6mm central aperture designed to make use of the principle of small aperture optics. When aligned on the line of sight of the non-dominant eye, in a mid depth corneal pocket, the KAMRA corneal inlay creates an improvement in depth of focus without having a significant impact on distance acuity.
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. Determination of which patients represent the best candidates for surgery and 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. This is where the art of medicine builds on the science and technology of a new procedure.
Now, some 2 ½ years and over150 inlays into the process of adding KAMRA surgery to our practice offerings, my experience has led to a series of observations that I believe will make surgical results more predictable for those considering becoming involved.
When performed correctly on the appropriate candidate managed correctly in the postoperative period, KAMRA has proven safe, predictable and very satisfying for both surgeon and patient. Stated simply, it works very well and delivers significant improvement in near visual function for patients. In fact, 98% of our KAMRA patients when asked about satisfaction respond in the affirmative and further state that they would recommend the surgery to family and friends. Essential in good outcomes in our experience is the management of appropriate patient expectations. KAMRA patients will almost universally see well at near with adequate light and good tear film. Patients need to know that dim light situations will always be somewhat problematic because of the very nature of the small aperture mechanism of the technology. Our recipients are educated to anticipate and supplement available light when required. Of great interest to me is that patients now approaching their 2-year surgical anniversary tell us that dim light functionality has improved significantly—likely due to enhanced neuro-adaptation. KAMRA surgery does not yield dry eye, however, recipients need to be educated to the fact that even the slightest tear film irregularity on that portion of the cornea anterior to KAMRA will have a negative influence on reading function. Long-term post ops quickly learn to manage this scenario with 5-10 rapid blinks as needed when near vision seems sub optimal. This very simple maneuver will redistribute tear film and improve the surface tear status. Distance acuity clarifies gradually over a 4-6 week period as the KAMRA pocket heals and light scatter diminishes.
What Makes for an Excellent Candidate for KAMRA Surgery?
We have implanted KAMRA successfully in patients between the ages of 40 and 65, who wish improvement of visual function at near. All candidates will responded positively to a standard KAMRA screening demonstration. With full distance prescription in place and a Lorgnette occluder blocking the dominant eye, reading off of a standard near card is attempted both with and without superimposed pinhole. Patients seeking KAMRA surgery will respond favorably if the ocular media is clear indicating a low level of light scatter.
A clear ocular dominance pattern appears to be associated with quicker neuro-adaptation to the small aperture of KAMRA. Approximately two-thirds of the population is right eye dominant, one third left eye dominant. These patterns are usually easy demonstrated with classical Miles or Porta testing (1). One percent of the population can demonstrate cross dominance where a potential patient can have dominance preference dependent on the activity at hand. The preferred eye for KAMRA placement in such individuals can be determined with mono vision testing superimposed over the distance prescription.
The most important element in determining candidacy for the KAMRA procedure is testing with Acutarget HD. This platform allows the surgeon to assess potential quality of vision as a function of light scatter (OSI or Ocular Scatter Index). Acutarget also allows for an accurate assessment of tear film stability–so very essential in the success with inlay surgery and it allows for the determination of the position of the first corneal Purkinge reflex relative to the pupil as guide for inlay centration in surgery.
Individuals with OSI scores of above 2.5, although likely to regain an adequate reading vision with good lighting are likely to lag in the return of distance vision or might actually lose lines of acuity. These candidates are often individuals who have had past LASIK surgery with mechanical bladed microkeratomes perhaps followed by laser enhancement procedures. These patients will require appropriate counseling before considering inlay surgery. Likewise, potential patients with demonstrable tear film instability will require treatment with documentation of improvement in this metric before surgery can be recommended.
In general, we see three categories of potential KAMRA candidates: the emmetropic presbyope, the ammetropic 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 post op management.
KAMRA and the Emmetropic Presbyope
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 post op steroids to Fluoromethalone 1% drops, which are taken 4x daily for two weeks with reduction to twice daily for weeks three and four week. Progress is followed with vision testing and serial Acutarget HD testing for OSI and tear film OSI mean readings with adjustments made in therapy as indicated. Pocket cases have the speediest recovery of both distance and reading acuity.
If pre operative evaluation reveals refractive error in the non-dominant eye it should be addressed with simultaneous laser vision correction with a post ablation target refraction of -0.50.
KAMRA and the Post LASIK Patient
Post LASIK KAMRA patients are approached in much the same way as pocket cases. Attention needs to be placed on the preoperative Acutarget HD measurement of OSI. Some of these 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 careful counseled on the impact this finding can have on the final visual outcome especially in the distance.
Studies have indicated that a manifest refraction of -0.50 represents the best situation for successful KAMRA surgery with levels of cylinder no higher than -0.50. as KAMRA centration issues are much more forgiving. 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 anticipating this development. 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 the above noted Fluoromethalone taper over the next four weeks. We have noted a rare tendency of PRK Kamra procedures to develop pocket haze at the two-month post op period. Vigilance is therefore advised with such patients.
KAMRA and the Myopic Ammetrope
Patients presenting 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 be offered 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 non dominant eye for -0.50) followed by KAMRA insertion one month later. A standard excimer ablation for the non-dominant eye is selected which 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.
KAMRA and the Hyperopic Ammetrope
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.
Experience has shown that KAMRA seems to work best with deeper placement in the cornea. On average we have placed the overwhelming majority of our inlays at a depth of 250 microns, however, when pre operative pachymetry indicate placement at depths of up to 275 microns have been used. It is my believe that there should be a minimum of 175 microns between the KAMRA pocket and Descemet’s membrane and have placed inlays at this depth without issues.
KAMRA inlay surgery should be performed making use of an atraumatic technique designed to minimize tissue trauma. The femtosecond laser created pocket should be opened in a smooth “one pass” approach with a well polished spatula dissector. Once released into the corneal pocket, the inlay position can be gently adjusted to assure precision in placement, however, heroic attempts at inlay position adjustment will often be met with reactive corneal haze. We make use of an irrigating Lindstrum to adjust the position of the inlay when indicated. Several drops of saline combined with a gentle sweeping movement will achieve the desired effect. Repositioning the inlay after the patient has left the treatment room is seldom worth the surgical trauma. In general, if the implanted eye has a mildly myopic refractive error inlay position can be surprisingly forgiving. Inlays positioned slightly nasal or inferior to the ideal Purkinge reflex landmark will do very well. Placement superior or temporal to the desired centration, however, should be adjusted in the manner described when identified at the time of initial inlay placement. Always remember that the KAMRA inlay is very forgiving of adjustment weeks and even months after the initial surgery.
Steroids use after KAMRA surgery should follow a standardized approach. For the overwhelming majority of our post op inlay patients we will use Prednisolone acetate 1% at a QID dosage for one week tapering to BID for the second week. Thereafter I prefer to use Fluormethalone QID for 2 week, BID for two weeks and then once daily for a final week. I have not seen long-term steroids as necessary except for one caveat—combined PRK and KAMRA. These cases rarely can develop haze as late a two months after surgery and should be kept on Flouromethalone one daily for 6 months as a hedge against this eventuality.