Martin L. Fox, MD, FACS
One year has passed since we added the Kamra corneal inlay to our menu of offered refractive procedures. KAMRA was the first FDA approved entry into the field of corneal inlay surgery aimed at the correction of presbyopia. It consists of a 3.8 mm microscopically thin disk of biocompatible material with a 1.6 mm central aperture. KAMRA achieves its effect by making use of the long-standing optical principle of small aperture optics allowing for the re establishment of an enhanced depth of focus. The KAMRA corneal inlay is placed in a femtosecond laser created corneal pocket at mid depth on the line of sight in the non-dominant eye. It restores the full range of near function while having minimal effect on distance acuity, a far cry from prior standards of presbyopia treatment including multifocal lenses, monovision contacts or laser vision correction.
In our refractive practice I have now placed over 70 inlays over the past year and I have had a chance to look back on my experience in order to reach some important observations on the effectiveness of this new technology and can now identify what essential elements are required to achieve great KAMRA outcomes.
After a full year of experience in the evaluation of candidates and managing them post operatively, I can now say without qualification that when KAMRA surgery is performed well on a good candidate that it safely produces very gratifying visual outcomes. In fact, 98% of our KAMRA recipients when asked report that they are very satisfied with their vision and would do the surgery again as well as and advise it for friends or family.
What makes for good KAMRA Candidacy?
Our experienced indicates that when individuals demonstrate a positive response of improved reading acuity with pinhole disk superimposition (Lorgnette or other) over the non-dominant eye they are likely to do well with KAMRA. Ocular light scatter determination with Acutarget HD will usually confirm a low level of scatter in such inviduals (below a grade 2 on a scale of 1-10). In preliminary evaluation it is important to establish and confirm the pattern of eye dominancy with standard Miles, Porta or visual blurring techniques as those who indicate an ambivalent pattern of dominancy may be masking muscle balance disorders that can create ocular confusion after surgery.
Candidates for surgery should be evaluated for tear film stability by tear break up time, vital dye tear film observation as well as by mean OSI over a twenty second testing period on Acutarget HD. Those who test sub optimally will need treatment to improve the pre corneal tear film before surgery can be anticipated.
The seminal work of Pablo Artal has indicated that small aperture optics work best when the eye is mildly myopic with low levels of astigmatism and higher order aberration. Not only do these patients do better in response to KAMRA but also they are much less sensitive to inlay decentration issues. Ideally one must strive to place the inlay aperture to coincide with the center of vision as indicated by the first Purkinge reflection, however, decentrations of up to 300 microns are well tolerated in mildly myopic individuals especially if the decentration is nasally or inferior.
Therefore, prospective patients who are outside of the ideal refractive range are best counseled to consider adjunct laser vision correction (LASIK or PRK) to bring them into the appropriate status of -0.50 to -0.75. This can be offered as a staged procedure or simultaneously with KAMRA implantation. We have observed that patients presenting with hyperopic refractive errors do very well with simultaneous LASIK and KAMRA surgery, whereas myopes of greater than -2.00 are best counseled towards a staged approach as these excimer ablations coincide with the KAMRA aperture and can result in lengthy delay in distance vision recovery in the implanted eye.
Our experienced with Intralase iFS (AMO) has been stellar as it creates excellent smooth pocket beds. Ziemer pockets are reported to be equally good, however, reports on early results on the FS 200 (Alcon) femtosecond laser have indicated that this platform may be suboptimal.
Patient Management and Expectations
Our results suggest that KAMRA works well and that the technology is here to stay as a viable choice in the correction of presbyopia. Part of our success with KAMRA can be attributed to the appropriate management of patient expectations. KAMRA surgery is in no way similar to LASIK, nor is its management. We have noted that 25% of our candidates read well and see at all distances within two weeks but that 75% will require 4-8 weeks to reach the therapeutic finish line. Most in this group will notice impressive near vision improvement within several days but can lag in distance acuity clarity. Corneal surface and customized steroid regimens are required as well as the confirmation of proper inlay centration, adequate tear film and reduction of post operative light scatter with guided healing are required to manage the recipient to excellent healing a