February 2012

 

NEWS & OPINION

 

Clarity for KAMRA


by Daniel S. Durrie, M.D.

   
The KAMRA corneal inlay

The KAMRA corneal inlay Source: AcuFocus

The AcuFocus KAMRA inlay

The AcuFocus KAMRA inlay for the treatment of presbyopia Source: Perry S. Binder, M.D.

The KAMRA corneal inlay by AcuFocus (Irvine, Calif.) is gaining traction as a great option for treating presbyopia in markets that have access to it, such as Europe, the Middle East, and Asia-Pacific. The inlay works based on the principle of small aperture optics and provides improved depth of focus to improve near vision while having minimal impact on distance vision. The KAMRA inlay is the result of decades of study on corneal inlays. Jose Barraquer is accredited to be the first to experiment with corneal implants in 1949.1 A series of improvements took place, but early generations of inlays suffered from poor predictability, loss of acuity over time, haze, corneal thinning, and decentration.2-4 The development of new biocompatible materials and experimentation with optimal placement, however, have changed the history of corneal inlays and the treatment of presbyopia. I first started working with hydrogel inlays to correct aphakia in 1985. The porous nature of the hydrogel material made these well tolerated by the cornea, whereas inlays made out of polysulfone caused corneal thinning and melting due to their poor permeability. This was one of the first indications that in order for an inlay to be tolerated by the cornea, the biological principals of the cornea must be maintained. That includes an inlay of material that allows glucose to go through the cornea and nourish the corneal epithelium. The KAMRA inlay has gone through six design iterations, starting with the original design that was made from Dacron fabric and was 25 microns thick. Over time, the platform has transitioned to polyvinylidene fluoride, a highly biocompatible material that is used routinely in IOL haptics. Further, the inlay has been reduced in size to just 5 microns thick in the current design. The number of microperforations has increased from 1,600 to 8,400, and these are arranged in a pseudorandom pattern to allow for appropriate nutrient flow and to minimize light scatter. Although melts occurred in a prior generation of inlay and with an earlier procedure, to date there have been no flap melts in the current clinical trial that will be submitted for approval next year.

In addition to the evolution in materials and design, numerous clinical studies over the past 7 years have led to the optimal depth placement in the cornea. Early studies demonstrated that shallow placement of the inlay has the potential to create some stress on the cornea, causing corneal shape change and thinning and ultimately resulting in an explant of the inlay. After performing a series of studies we also found that if the inlay was implanted too deeply, we had much lower visual recovery. The inlay should be implanted at an optimal depth of 200 microns. When kept at this depth, the cornea tolerates the inlay very well. Development in other areas of ophthalmology has also aided in the advances in the corneal inlay procedure. The femtosecond laser allows surgeons to program what they want, and then it is executed with precision. This permits them to not only control the depth, but also the configuration of the incision. The precision of the laser allows us to make pockets at certain locations in the cornea, aiding with centration. Another new technology now in use, the AcuTarget System, provides surgeons with real-time inlay placement guidance within 100 microns of the intended placement location, as well as objective placement assessment post-op. This surgical aid has the potential to reduce procedure time, resulting in quieter eyes in the immediate post-op period. In addition to historical data dating back to the 1960s, in-depth, international, multicenter clinical trials have provided evidence of the safety and efficacy of the KAMRA corneal inlay. With the transition from an investigational product for many years to a commercially available product outside of the U.S., there are now over 8,000 inlays implanted in Japan, Australia/New Zealand, Europe, the Middle East, and South America, without any corneal thinnings and with good patient satisfaction.

References

1. Barraquer JI. Queratoplatica Refractiva. Estudios e informaciones Oftalmologicas. 1949;2:10.

2. Deg JK, Binder PS. Histopathology and clinical behavior of polysulfone intracorneal implants in the baboon model. Polysulfone lens implants. Ophthalmology. 1988;95:506-515.

3. Ali JL, Mulet ME, Zapata LF, Vidal MT, De Rojas V, Javaloy J. Intracorneal inlay complicated by intrastromal epithelial opacification. Arch Ophthalmol. 2004;122:1441-1446.

4. Choyce P. The present status of intracameral and intracorneal implants. Can J Ophth.1968;3:295-311.

Editors' note: Dr. Durrie has financial interests with AcuFocus.

Contact information

Durrie: 913-491-3330, ddurrie@durrievision.com

Related articles:

The KAMRA corneal inlay experience: One-year observations by Martin L. Fox, MD, FACS

Positive reviews for the KAMRA corneal inlay by Lauren Lipuma EyeWorld Contributing Writer

KAMRA inlay recommended for approval by FDA panel by Ellen Stodola EyeWorld Staff Writer

Optimizing KAMRA inlay clinical outcomes by Minoru Tomita, MD, PhD

Whos the best candidate for a corneal inlay? by Vanessa Caceres EyeWorld Contributing Writer

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