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Cataract Surgery | Sep 2012

IOL Implantation After a Kamra Corneal Inlay Procedure

This inlay does not have to be explanted before cataract surgery for successful results.

Currently, an estimated 1.7 billion people worldwide have presbyopia.1 Combine the high prevalence of presbyopia with the fact that cataract is the leading cause of treatable blindness worldwide,2 and it is obvious there will soon be a significant overlap between these two populations. As presbyopia often develops at a younger age than cataract, it is increasingly common to perform cataract surgery on a patient who previously underwent presbyopia correction. Therefore, we must start considering how these two treatments can affect each other.

Surgical and nonsurgical options for presbyopia correction range from glasses and bifocal or multifocal contact lenses to PRK, conductive keratoplasty, and corneal inlays. As an investigator for the Kamra corneal inlay (AcuFocus, Inc.), I have found that not only is corneal inlay implantation an excellent means of treating presbyopia, but also it can enhance later cataract surgery.

MULTICENTER STUDY

The Kamra inlay increases depth of focus using the principle of small-aperture optics. This implant restores near and intermediate visual acuity without significantly affecting distance vision. In order for it to work, 8,400 microfenestrations are pseudorandomly distributed across its surface. These microfenestrations, 5 to 11 μm in diameter, support the natural corneal metabolic process and minimize photic phenomena.

Results of an international multicenter clinical trial of the Kamra inlay showed substantial near visual acuity gains at 24 months.3 The study included 507 patients who had an inlay implanted in their nondominant eye. Before surgery, mean near, intermediate, and distance UCVA were J8, 20/32, and 20/20, respectively.

During the procedure, a femtosecond laser was used to create a lamellar incision, and the inlay was implanted at a depth of 200 µm. At 24 months, mean near UCVA improved to J2 in the 429 patients available for follow-up, representing an average gain of 3.2 lines. Mean intermediate UCVA improved to 20/25, and mean distance UCVA remained virtually unchanged.

SUBSEQUENT CATARACT SURGERY

Two of my patients who underwent monocular Kamra inlay implantation with great success developed bilateral posterior subcapsular cataracts 3 years postoperatively. In both cases, I performed cataract surgery and IOL implantation without explanting the Kamra inlay (Figures 1 and 2). The inlay enhanced visual outcomes for these patients and, most important, did not result in any negative consequences for the cataract surgery.

In both patients, the IOLMaster (Carl Zeiss Meditec) was easily able to take a biometry reading through the center of the inlay, and the process of determining IOL power was not altered. In comparison, treatments such as PRK or LASIK create an abnormal corneal shape, which can result in greater difficulty performing accurate IOL power calculations.

The inlay does not limit the kind of IOL that can be used, nor does the lamellar incision required for inlay implantation affect cataract surgery. On the other hand, in eyes that have previously undergone radial keratotomy, cataract surgery incisions are more difficult to create and the eye is less stable for the first 1 or 2 months after cataract surgery. None of this applies to cataract surgery after the Kamra inlay, and patients retain the positive benefits of the Kamra inlay after cataract surgery, such as improved depth of focus.

PEARLS

Because of the Kamra corneal inlay’s mechanism of action, aiming for a small amount of myopia in the postoperative refraction can strengthen near vision without affecting distance vision. The inlay can also improve the resulting visual system after toric IOL implantation. In the future, there may be potential for insertion of a smallaperture inlay to improve vision in an unhappy multifocal IOL patient.

A couple of important factors are crucial for success with cataract surgery after corneal inlay implantation. First, ensure that the pupil is well dilated. A pupil dilated to at least 6 mm ensures that the surgeon has plenty of space to see around the 3.8-mm, semi-opaque inlay. Additionally, tilting the eye during phacoemulsification provides the surgeon with a view around the implant. This maneuver allowed me to anticipate what the phaco probe was doing.

Second, because the Kamra inlay provides approximately 2.50 D of depth of focus, patients can tolerate some of the negative effects of unintended residual refractive error (myopic or hyperopic) after cataract surgery better than if the inlay was not left in the eye. The same is true with astigmatism. To achieve optimal near and intermediate vision without sacrificing distance vision, however, it best to aim for approximately -0.75 D of myopia in the inlay eye.

CONCLUSION

In my experience, the Kamra corneal inlay enhances the results of cataract surgery. This makes Kamra one available presbyopia-correcting procedure that continues to work as effectively after cataract surgery as before.

Kevin L. Waltz, OD, MD, practices at Eye Surgeons of Indiana in Indianapolis. Dr. Waltz states that he is a paid consultant to AcuFocus, Inc. He may be reached at e-mail: kwaltz56@ gmail.com.

  1. Market Scope, LLC. 2011 Global presbyopia-correcting surgery market.
  2. World Health Organization. http://www.who.int/blindness/Vision2020_report.pdf. Accessed July 30, 2012.
  3. Data on file, AcuFocus.

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