Keratoconus has long posed a complex challenge for corneal surgeons—its hallmark irregular astigmatism, progressive thinning, and ectasia often limit the efficacy of traditional optical and surgical interventions.1 While corneal cross-linking has provided a means of stabilizing the disease, restoring corneal regularity and improving visual function remain persistent hurdles.
Corneal tissue addition keratoplasty (CTAK) represents an innovative step forward in addressing these limitations.2 This novel intrastromal lamellar keratoplasty technique employs a customized, acellular, gamma-irradiated corneal tissue inlay designed to recontour the keratoconic cornea while preserving native tissue integrity.3
Overview of CTAK for keratoconus
Originating from early efforts with preserved corneal tissue inlays, CTAK has undergone significant refinement to achieve both structural and visual rehabilitation. Initial prototypes demonstrated dramatic improvement in corneal shape but were limited by interface opacity over the pupil.
The evolution to a pupil-sparing lamellar design has transformed outcomes—combining biomechanical reinforcement with optical clarity.3 In a prospective clinical trial of 21 eyes, uncorrected visual acuity improved by an average of 2 logMAR lines in 96% of eyes and 6 logMAR lines in almost 50% of eyes, with substantial reductions in refractive error and keratometric steepening.
These findings, supported by over 150 successful cases performed by multiple surgeons, underscore CTAK’s safety, reproducibility, and potential as a transformative approach in the keratoconus treatment paradigm.3
Beyond its impressive results, the strength of CTAK lies in its individualized customization. Each inlay is meticulously designed to match the patient’s corneal topography and tomography—varying in thickness, arc length, curvature, and position—to optimize corneal symmetry and visual outcomes.3
As experience with this technique grows, CTAK is emerging not only as a reconstructive option for advanced keratoconus but also as a tailored, tissue-based intervention that bridges the gap between cross-linking and transplantation. In this article, Evan D. Schoenberg, MD, shares his experience with CTAK.
For guidance on how to use anterior segment imaging for surgical planning in CTAK, check out Advanced Diagnostic Imaging in Keratoconus!
What are your thoughts on CTAK as an improved surgical option for keratoconus?
CTAK is an evolution of an idea that we've been working with for a long time for keratoconus.
It's very exciting that it's reaching the public eye and becoming a popular option, because I think for too long, keratoconus patients have been told they don't have a good in-between option with a corneal transplant at one extreme and either needing to use specialty contact lenses or just dealing with poor vision at the other.
For many, many years, the idea of reshaping the cornea in some way has been present for many cornea specialists. In the space of additive technology, we've had INTACS, which was popular decades ago and then fell out of favor due to concerns with consistency and potential complications, but regained some popularity with the advent of femtosecond laser-assisted INTACS, with which we saw some good success in my clinic.
Still, INTACS patients often experienced substantial glare, effect was somewhat limited, the result was cosmetically undesirable for some patients as the implant was quite visible to others, and risk of extrusion could lead to late complications.
From INTACS, we evolved into CAIRS (corneal allogenic intrastromal ring segments), a technique developed by Dr. Soosan Jacob and first described in 2018. This was a huge step forward, utilizing shaped corneal tissue rather than rigid polymethylmethacrylate (PMMA) to achieve improved corneal curvature.
CTAK is the latest iteration in this concept of additive keratoplasty:
- INTACS was additive using rigid plastic segments, with limited customization available in the United States, but more extensive options available elsewhere.
- CAIRS started with “one size fits most” slivers of corneal tissue, and surgeons can further customize the tissue manually based on nomograms (the most popular of which are the Jacobs, Istanbul, and Awwad nomograms) or their own clinical judgement.
- CTAK has taken this idea and turned the customization into something that's much more of an “easy button” by applying a nomogram developed by Drs. Hersh and Greenstein, which features some proprietary customizations, and providing a treatment recommendation along with femtosecond-cut bespoke tissue segments of specified arc length, thickness, inner diameter, and outer diameter.
What are the advantages of CTAK?
When transitioning from CAIRS to CTAK, I offer this explanation to patients who have undergone CAIRS for their first eye, but will receive CTAK for the second: “This is the same surgery. We're just using corneal tissue that's even more specifically designed for your topography and needs.”
Moving to CTAK from CAIRS has streamlined my day of surgery while providing consistently excellent plans, and the tissue segments are easy to handle and cosmetically nearly invisible to the naked eye after implantation.
When you look at published results on CTAK, the results shared by the author are very similar to the results that I got doing an analysis internally of my CAIRS results. I was using a gestalt nomogram for CAIRS, so I was doing some customization based on the topography and tomography.
My internal results were essentially ~2.5 lines of uncorrected acuity improvement, 50% reduction in astigmatism, and 2.25 lines of best corrected acuity improvement.
Both CAIRS and CTAK are amazing procedures; however, CTAK is just an easier button to push for most surgeons, rather than figuring out how to customize the CAIRS tissue to the patient. That sort of ease isn't just good for that one patient—it's good for the entire system because it offers a lower barrier to entry for surgeons to get involved.
I think CTAK is going to go mainstream, not because it's that much better of a procedure than CAIRS, although theoretically it may reach better levels, but because it's just so easy for a good surgeon to adopt using the tools and the assistance that having that tissue confidently made for that patient produces.
What are your guidelines for patient selection?
Ideally, those best suited for CTAK and individuals with:
1. Mild to moderate keratoconus
Predominantly, CTAK is intended for the mild to moderate keratoconus patient. It can be considered in severe cases, but it's more of a “Hail Mary.”
As such, the patients I've seen the most success with tend to have visual acuity in glasses in the 20/30 to 20/80 range, and they tend to get a 2.5-line improvement in vision from that level.
I've seen some patients gain meaningful improvement who have worse keratoconus—but if you take a patient who's 20/400 and you help them achieve 20/80, they can be excited about it, but they're still not going to feel like they're now able to use glasses instead of their scleral contact lens.
So, in a select patient with more severe keratoconus, it can be attempted, but it just requires a bit more counseling about expectation management.
2. Clear line of sight
Beyond that, CTAK is best suited for patients with clear visual access; it is not a cure for corneal scarring.
3. Dissatisfaction with current vision correction
If it ain't broke, don't fix it. CTAK is less for the population of people who have a perfect solution that works really well for them and more so for people who are saying, “I enjoy a scleral lens, but I can only wear it for 4 hours a day, and I want to be able to be successful in glasses the rest of the time.”
After CTAK, the patient who sees 20/20 in their scleral but 20/80 in glasses may be able to see 20/40 in glasses, while still being refit with a scleral to see 20/20.
4. Contact lens intolerance
Patients who are chronically contact lens intolerant can be excellent candidates as well; however, lenses can also be refit after surgery. Thus, the patient ends up with two options: a more acceptable vision quality in glasses, plus a scleral contact for absolute best vision.
Surgical pearls for CTAK success
- Pearl 1: Since everything comes down to where you're positioning the inlay, centration is very important. Depending on your surgical setup, it may be challenging to determine the center of the cornea when the patient is supine under the microscope.
- For example, the Alcon WaveLight EX500 that I use in my LASIK suite has a bit of a parallax, so when you're looking down at the eye, what looks like the center is actually slightly off-center.
- Therefore, I like to do my initial marking at the slit lamp before I lay them flat for surgery—similar to how you might do your alignment marks for a toric lens with the patient sitting up, before laying them flat for cataract surgery. The other marks that you make can all be based around that center spot.
- Pearl 2: Having the right instrumentation is very important. There's a beautiful set of instruments that have been designed for the procedure.
- I started off using all the instruments I'd been using for INTACS previously, but I transitioned to the long curved forceps that grasp the tissue from the tip back and allow smooth insertion.
- These forceps allow the tissue to slide into the channel very atraumatically and, typically, without having to do any extra work to access it from another angle.
- Pearl 3: You don't have to push the tissue all the way to its destination. Once you get the tissue past the lip of the incision and the majority of it is in the cornea, you can spread it out using gliding motions on the surface.
- As long as you've dissected the channel very well, it will extend itself into the channel. So before you ever put that tissue in, be sure to dissect the channel open completely—360°—so there's no resistance as that tissue is gliding in.
- Pearl 4: Remember that CTAK is focused on visual improvement, but as of yet, we don't have any evidence that it stabilizes keratoconus. So CTAK is not a replacement for corneal cross-linking, which is the gold standard for stabilization. It is an adjunctive procedure.
In conclusion
CTAK represents the culmination of decades of innovation in additive corneal surgery, offering ophthalmologists a practical and highly customizable tool to enhance visual outcomes for patients with keratoconus.
By combining the precision of femtosecond laser–guided customization with the biocompatibility of donor corneal tissue, CTAK bridges the gap between corneal cross-linking and transplantation.
As early results continue to validate its reproducibility, accessibility, and safety, CTAK is poised to become a mainstream option that empowers more surgeons to offer individualized, tissue-based solutions.
With continued refinement and growing clinical experience, this technique holds promise to redefine the standard of care for keratoconus management.
