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.
Now, 2.5 years and more than 200 inlays into the process of adding Kamra (AcuFocus) surgery to our practice offerings, my experience has led to observations that I believe will make surgical results more predictable for those considering becoming involved (as have others, as evidenced starting on page 22).
When performed correctly on the appropriate candidate and managed correctly in the postoperative period, Kamra has proven safe, predictable and very satisfying for both surgeon and patient. It works well and delivers significant improvement in near visual function for patients. Ninety-eight percent of our Kamra patients are satisfied with their choice and say they would recommend the surgery to family and friends. Others have found similar results.1
KAMRA IN THE REAL WORLD
I was among the first wave of surgeons trained to install the Kamra, and I realized almost immediately that the ideal Kamra patient, the plano presbyope, didn’t really exist. Most patients complaining solely of early difficulty with reading acuity are mildly hyperopic. With this typical low hyperope, we quickly learned that if a Kamra inlay was placed in a pocket procedure alone to address reading complaints without correcting the underlying mild hyperopia that Kamra outcomes were suboptimal. It was quickly realized this patient required a combined Kamra/LASIK procedure with ablation target for a mildly myopic outcome to enjoy a great outcome — a procedure I have dubbed “pan-LASIK.”
While Kamra patients will almost universally see well at near with adequate light and good tear film, they need to know that dim-light situations will always be somewhat problematic because the technology itself interferes with intraocular light transmission. If the implant lies inferior or nasal that is OK. Otherwise, be it superior or temporal, the patient may have problems with shadows.
Our patients learn to anticipate and supplement available light when needed. Of great interest is that recipients nearing their two-year surgical anniversary tell us dim light functionality has improved significantly — likely due to enhanced neuro-adaptation.
Kamra surgery does not yield dry eye, so recipients need to learn that the slightest tear film irregularity on that portion of the cornea anterior to Kamra will have a negative influence on reading function. Long-term postops quickly learn to manage this scenario with five to 10 rapid blinks when near vision seems suboptimal. This simple maneuver will redistribute tear film and improve the surface tear status. Distance acuity clarifies gradually over a four- to six-week period as the Kamra pocket heals and light scatter diminishes.
RIGHT EYE, RIGHT PATIENT
A clear ocular dominance pattern appears to be associated with quicker neuro-adaptation to the small aperture of Kamra. Two-thirds of the population is right-eye dominant, the rest left-eye dominant. These patterns can easily be tested with Miles or Porta testing.2 One percent of the population can demonstrate cross dominance; the activity at hand will determine the dominant eye. The preferred eye for Kamra placement in such individuals can be determined with monovision testing identifying the preferred reading eye.
The most important element in determining candidacy for the Kamra procedure is testing ocular light scatter as a metric of visual quality with AcuTarget HD (Visiometrics). The AcuTarget HD allows the surgeon to assess potential vision quality as a function of light scatter (Ocular Scatter Index, or OSI). The AcuTarget HD also allows for an accurate assessment of tear film stability, enabling the surgeon to determine the position of the first corneal Purkinje reflex relative to the pupil as guide for inlay centration.
Individuals with OSI scores 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 LASIK surgery with mechanical-bladed microkeratomes perhaps followed by laser enhancement procedures. These patients require appropriate counseling before considering inlay surgery. Likewise, potential patients with demonstrable tear film instability require treatment with documented improvement in this metric before surgery can be recommended.
If pre-operative evaluation reveals refractive error in the nondominant eye, it should be addressed with simultaneous laser vision correction with a post ablation target refraction of -0.50.
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 -0.50.3
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 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.
Since FDA approval, AcuFocus has changed the recommendation for the inlay’s placement to be made deeper into the cornea.4 On average, we have placed the overwhelming majority of our inlays at a depth of 250 μm; however, when pre-operative pachymetry indicates deeper placement, we have used up to 275 μm. It is my belief there should be a minimum of 175 μm between the Kamra pocket and Descemet’s membrane; I have placed inlays at this depth without issues.
Kamra inlay surgery should be performed with use of an atraumatic technique designed to minimize tissue trauma. The femtosecond laser-created pocket should be opened with 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 are often met with reactive corneal haze. We make use of an irrigating Lindstrom cannula to adjust the inlay’s position when indicated. Several drops of saline combined with a gentle sweeping movement 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 positioning can be surprisingly forgiving. Inlays positioned slightly nasal or inferior to the ideal Purkinje reflex landmark will do very well here. Placement superior or temporal to the desired centration, but should be adjusted in the manner described when identified at the time of initial inlay placement.
With these patients, use of steroids postsurgery, again, should follow a standardized, tapered approach, generally lasting about six weeks. OM
- Moshirfar M, Quist, TS, Skanchy DF et al. Six-month visual outcomes for the correction of presbyopia using a small-aperture corneal inlay: single-site experience. Clin Ophthalmol. 2016 Nov 2;10:2191-2198.
- Schwarz C, Manzanera S, Prieto PM et al. Comparison of binocular through-focus visual acuity with monovision and a small aperture inlay. Biomed Opt Express. 2014 Sep 2;5:3355-3366.
- Artal P, Tabernero J. “Optical Modelling in Real Eyes Of a Corneal Small Aperture Inlay to Increase Depth of Focus. Investigative Ophthalmol Vis Sci: April. 2011;52:14.
- Stoneback R. Patient data bring Kamra into focus. Ophthalmol Mgmt. Jan. 2017; 21:14-18.