Long-term data assures further growth in interest of corneal-based treatment
There are an estimated 1.6 million presbyopes worldwide, and that number is growing.1 In addition, these patients often present with concomitant refractive error or prior refractive surgery. This has driven demand for greater understanding of this group and better treatment options. In response to this demand there is growing interest in a corneal-based treatment for this condition.
The KAMRA corneal inlay (AcuFocus) is currently commercially available in over 40 countries, and with over 17000 inlays implanted worldwide, it is proving to be an excellent option for presbyopes who desire freedom from spectacles. The mechanism of action is based on the small aperture concept, which improves near and intermediate visual acuity (VA) by increasing depth of focus. Three independent recently peer-reviewed published studies all report that the small aperture inlay is both an effective and stable treatment for presbyopia.
Further, additional long-term results were published for 32 patients that participated in an international, prospective, nonrandomized, non-comparative cohort study.3 Preoperatively, patients had a mean UNVA of J6, a mean uncorrected intermediate visual acuity (UIVA) of 20/40, and UDVA of 20/16 in the non-dominant eye as well as bilaterally. Three years postoperatively, mean monocular UNVA improved to J1, with 97% achieving J3 or better. Mean UIVA improved to 20/25 with 91% achieving 20/32 or better in the inlay eye. Mean monocular UDVA dropped slightly to 20/20, with all eyes achieving 20/32 or better. Binocular UDVA remained unchanged. Improvements in near and intermediate VA were statistically significant, as were the differences between VA in the treated and untreated eye.
No inlay was explanted and no inflammatory reactions were observed. Two inlays had to be re-centred 6 months after implantation to improve VA, due to an insufficient increase in near and intermediate visual acuity and a concomitant decrease in UDVA. No patient had detectable central visual field defects and contrast sensitivity remained within normal limits. The study also shows that the principles of small-aperture optics are not impacted by the progressive nature of presbyopia: there was no change in VA over three years in the inlay eye, whereas in the fellow eye, decreased near VA is apparent.
Addressing the concerns about biocompatibility, there are patients in the study that have had the inlay for up to four years maintaining clear corneas. These results support the safety and efficacy of the corneal inlay as a treatment for presbyopia by increasing the depth of field, and the compromises are minor compared to the positive benefits of a significant increase in depth of focus and the ability to maintain a good distance vision. Preoperatively 87.5% of patients reported dependence on reading glasses most or all of the time, while postoperatively after 3 years only 6.3% of patients remained dependent on reading glasses most of the time.
It is important to note that both of these long-term studies are evaluating the outcomes of the inlay generation just prior to the currently commercially available KAMRA inlay design. Both generations are made of polyvinyledene fluoride (PVDF) with nano-particles of carbon incorporated to make it opaque. Both inlays, measure 3.8 mm in total diameter with a central aperture, or opening, of 1.6 mm. The generation evaluated in the long-term papers had only 1600 micro-perforations each measuring 25 μm in size. The current, commercially available version of the inlay now has 8400 micro-perforations, which vary in size from 5 to 11 μm and are arranged in a pseudo-random pattern. The inlay profile has also been reduced from 10 μm in the prior generation to 5 μm which means that light transmission rate is now 5%, versus 7.5% with the prior design. The changes in inlay design between generations were made to minimize corneal curvature influence, support natural corneal metabolic function and minimize any photic phenomenon.