Eyeworld

64 | EYEWORLD | SUMMER 2026 C ORNEA References 1. Greenstein S., et al. Corneal tissue addition keratoplasty: new intrastromal inlay procedure for keratoconus using femtosecond laser-shaped preserved corneal tissue. J Cataract Refract Surg. 2023;49:740–746. 2. Samuel A, et al. Corneal bio- mechanical changes following corneal allogenic intrastromal ring segment (CAIRS) implan- tation. ASCRS Electronic Poster, 2024 ASCRS Annual Meeting, April 5–8, 2024. 3. Friedrich M, et al. Visual and topographic outcomes after corneal allogeneic intrastromal ring segments for keratoco- nus: a systematic review and meta-analysis. Am J Ophthalmol. 2025;276:81–91. channels where these segments are placed are created, it's relatively straightforward, he said. That's a convenient way for many surgeons to start, especially if they already have the laser. The alternative is a manual strategy for creating the channel. Manual dissection has a steeper learning curve and presents a bit more of a challenge for the starting surgeon, Dr. Parker said. However, it doesn't use the laser, so for surgeons who don't have access to the laser or who don't want to use the laser, the manual technique is a way to get started. Dr. Jacob mentioned a comparison to syn- thetic segments, however, she noted that these can be prone to melt, so you have to be careful to have a lot of stroma above a synthetic seg- ment. Because of this, it's placed very posterior. You can't treat patients below a certain thick- ness. In CAIRS, you can decrease the optical zone, implant thicker segments, and implant more superficially, Dr. Jacob added, which al- lows you to treat more advanced cases. While both allogenic and synthetic seg- ments allow for customization, Dr. Jacob said synthetic options may only be customized with linear gradation and not as true customization because "customized" synthetic segments are manufactured in stock sizes. With CAIRS, she has described custom shaping since 2017, and you can individually shape it for each eye of a particular patient. Keratoconus is never the same in any two patients or two eyes, so there's no way that you can treat it without custom- izing, and custom shaping is simple with her nomogram, she said. Dr. Jacob noted she uses the double-blad- ed trephine (Jacob CAIRS trephine, Madhu Instruments) that is available in various sizes to cut the tissue, and this provides results that are just as accurate as using a laser because of the precise computer numerical control nature of the manufacturing technology. The added advantage is that you can get the full thickness of the tissue, unlike with the femtosecond laser, which allows only partial thickness cuts, she said. This allows potentially greater flattening with the special double-bladed trephines while still allowing for the tissue to be split and used if required. "Another big advantage of manual shaping is that you can customize it exquisitely," she said. With the femtosecond laser, you can customize, but you would need a lot of calcula- tions, and even then, there are certain limita- tions. There are several differences to using an allogenic inlay to a synthetic option, Dr. Parker said. He finds that one advantage of an allogen- ic is it's not a foreign material that the body is trying to spit out. "When you have something like a piece of plastic, the body may try to reject that," he said, and it can extrude out through the front surface of the eye over time. When that occurs, it could be a disaster with corneal melting and potential infection. With allogenic inlays, the body doesn't have that same natural tendency to reject them. As a result, he thinks that's safer to put inside of the eye. "Furthermore, you can use bigger segments, which have a greater topographic effect, and you can place them more anterior in the cornea, which also has a more topographic effect," he said. Finally, you can use them in thinner corneas. With CAIRS and CTAK, you can place big segments higher in the cornea, and in patients with much thinner corneas, you get much more of an effect. continued from page 63 Preop, postop, and difference maps after custom-shaped CAIRS for keratoconus Source: Soosan Jacob, MD

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