Feb 10, 2016
Corneal Inlays: are they the “ Silver Bullet “ Treatment for Presbyopia?
by John F. Doane, MD, FACS, FAAO Internationally Known & Respected Corneal/Refractive/Cataract Surgeon
Discover Vision Centers, Kansas City Missouri & Kansas
The short and very direct answer is absolutely no. If you have an interest in this topic please read on as I can share 15 years of experience performing and following intracorneal inlays in an FDA clinical trial. It is important to know that refractive corneal inlays and onlays are not new. They have been studied for over 50 years with no commercial success to date. As a matter of perspective katatophakia lost out to intraocular lenses for the treatment of aphakia after cataract extraction 50 plus years ago and as you will see below the cornea loses out to the IOL again when we compare inlays to presbyopia correcting IOLs. As successful as corneal laser refractive surgery has been world-wide with over thirty million eyes treated the same cannot be said for corneal inlays or onlays. The recurring theme has been long-term bio-incompatibility. From my personal perspective I wish inlays and onlays did work. I have learned more about corneal physiology after being involved in corneal inlay work and am indebted to all the knowledge I have gained. That being said the results, good or bad, promising or not are the basis for why we do or do not recommend procedures to family, friend and patients alike.
To judge any refractive device or technique I think it is important to know and understand the devices or techniques purported visual acuity effectiveness, refractive predictability, refractive stability, safety and quality of vision and then compare this to other available techniques. For a new technology to unseat the status quo it obviously has to out-perform the status quo. If it does not then the technology is dead on arrival to the commercial market. In their current iterations I believe the three corneal inlays being proposed to resolve presbyopic complaints that are either currently FDA-approved or in process of approval simply miss these metrics and are not game changers for patients who abhor presbyopia and its remedy with glasses or contact lenses.
Let us first look at visual effectiveness. Effectiveness in refractive surgery analysis specifically looks at the percentage of eyes that attain a certain level of function, i.e. uncorrected distance acuity of 20/40 or uncorrected near acuity of J-3. The current status quo effectiveness threshold for success is roughly 20/20 at distance and J-1 at near. Anything less than this and patients in general will want more. In the days of radial keratotomy we ( practitioners ) were elated to have everyone seeing 20/40 or better ( as a side note, I never performed RK but did follow patients as a resident and fellow ). With the advent of laser vision correction the suitable goal metric is now 20/20 or better for distance. For near acuity when either dealing with monovision or multifocal IOL technology J-1 or better unaided is the threshold. The reason J-1 is required is not because patients routinely read J-1 print because we rarely do in our daily lives. The reason we need J-1 ability is because we need to be able to sustain reading larger print, J3 or J-5, for extended periods of time without fatigue. If a refractive device be it surgical, glasses or contact lenses can only support J-3 acuity the patient will fatigue relatively quickly and vocalize their difficulty. So, what do the inlays provide? Reports from AcuFocus on its Kamra pin-hole device are that 83.5% of patients see J-3 or better. 1 In translation this means that 16.5% do not see J-3. More importantly let us look at J1, J2 and the distance acuity. For the most experienced KAMRA surgeons in the world 41% of treated eyes were J-1, 68% were J-2, and 81% were J-3 unaided, respectively at 12 months postoperatively. 2 And from this same study, 81% of eyes were 20/20 unaided at distance. As a comparison, multifocal IOL technology ( Tecnis Multifocal ) all patients could read J2 or better and 90% could read J1. 3 From this study it is also important to note that 25% of eyes required corneal refractive surgery to alleviate residual sphere or astigmatism to achieve these results. From my perspective this is completely within reason. MFIOL are more powerful. Yes they require more work, some needing LVC enhancement, but in the end, they provide a superior result at distance and near. In a retrospective review of 2500 eyes of 1558 patients implanted with the Tecnis® Multifocal IOL (minimum of three months follow-up), 85% of patients achieved 20/30 BCVA at distance and 94% achieved J1 vision. Five percent of eyes required enhancement after initial surgery, but no eyes required lens exchange.4
In the above we indirectly discussed predictability. Inlays for pure presbyopia essentially have perfect predictability as the refraction is not being altered. Presbyopia correcting IOL’s will have a definite enhancement rate so one could say they are not as predictable but I personally believe this takes a huge back seat to effectiveness where IOL’s are superior to inlays. From a stability standpoint IOL’s are superior once the refractive target is obtained. Due to long-term bio-incompatibility the refraction does change with inlays and this is where the wheels fall off the wagon for inlays. The same can be said for safety. With bio-incompatibility comes lost lines of best corrected vision with inlays. Lastly we can discuss quality of vision. Quality of vision can be directly correlated with explantation rates at least for multifocal IOL’s. In our practice this is 1% of MFIOLs. What is the explantation rate of corneal inlays? From AcuFocus FDA data we know this to be > 3% of inlays at 1 year. At 5 years AcuFocus reported 8.9% (45 of 508 subjects) had elected to remove the Inlay, the majority of which were removed to resolve visual complaints.5 I personally believe this number is actually quite higher in the real world. My guess is that it will be closer to 10-15% post-approval at 3-5 years from implantation and will only increase with time due to inlay bio-incompatibility.
In summary, the current iteration of inlays in my personal experience and evaluation of current data when compared to presbyopia correcting IOL’s do not perform sufficiently. As the above is a prediction and I could be wrong I will happily wait on the sidelines to see if what I am predicting will come to pass.
1. FDA approves first-of-its-kind corneal implant to improve near vision in certain patients. US Food and Drug Administration. April 17, 2015. Accessed October 6, 2015.
2. Inlays and Presbyopia: The Next Frontier - A look at three leading approaches using inlays to expand presbyopic patients’ range of vision. Review of Ophthalmology, http://www.reviewofophthalmology.com/content/c/46512#sthash.LIzbL3bI.dpufhttp. Accessed 10-6-2015.
3. Goes FJ. Visual results following implantation of a refractive multifocal IOL in one eye and a diffractive multifocal IOL in the contralateral eye. J Refract Surg. 2008;24(3):300–305.
4. Akaishi L, Vaz R, Vilella G, et al. Visual performance of Tecnis® ZM900 diffractive multifocal IOL after 2500 implants: a 3-year followup. J Ophthalmol. 2010;2010 Pii717591.
5. Kamra Inlay Professional Use Information. http://www.accessdata.fda.gov/cdrh_docs/pdf12/P120023d.pdf; accessed 10-12-2015