The Evolution of CAIRS

Dr Soosan Jacob’s corneal allogenic intrastromal ring segments (CAIRS) have provided surgeons worldwide with a valuable option in keratoconus treatment. Since then, the technique has been further developed to facilitate insertion and reduce the risk of ocular graft versus host disease and postoperative infections.

“When I started implanting CAIRS, my team and I asked ourselves: How can we make the insertion easier? How can I put more volume into the cornea? How can I reduce the risk of rejection and infection?” said Farhad Hafezi MD, PhD. “We were wondering if it was the volume or the stiffness that gave the topographical effect. Last and not least, we were also considering the risk of implanting a graft from a donor with an unchecked keratoconus.”

One of the first difficulties a new surgeon may encounter when dealing with the original CAIRS technique or with precut segments (Keranatural/Optigraft/CTAK) relates to the soft and floppy nature of the untreated allogenic graft, Professor Hafezi observed. Even the ingenious solution proposed by Dr Shady Awwad of the “jerky technique”, from Prof Hafezi’s perspective, comes with a challenge: while working like a charm for the first few seconds, as soon as the graft comes in contact with some humidity on the ocular surface, the graft thickness starts to vary and the segment can rapidly lose stiffness if not implanted quickly enough. In the hands of a true master like Dr Awwad, this is not a problem, and it can be an incredibly fast technique, Prof Hafezi noted.

Although rare, anterior stromal melt can occur with CAIRS implantation. The implantation of CAIRS segments is a transplantation of living keratocytes. It has lower risk of postoperative dysphotopsia or glare, extrusion, and erosion when compared to synthetic alternatives. The gamma ray sterilisation of precut segments, on the other hand, sensibly increases the cost for any graft personalisation option, as the tissue is processed in the eye banks.

While troubleshooting CAIRS, Prof Hafezi selected five pivotal questions that needed one answer, one solution: How to make the insertion easier? How to insert more volume? How to avoid rejection? How to avoid infection? And, finally, what if my donor had keratoconus? The answer to all of these questions is cross-linking, he said. Cross-linking is a procedure that modifies the physiology of the cornea in many ways, largely addressing the five questions about CAIRS, he added.

To refine his version of CAIRS, called ECO-CAIRS, Prof Hafezi carefully analysed the properties of cross-linked stromal tissue in search of the best possible procedure to achieve the correct stiffness—especially a stable thickness of the graft. It is the volume that drives the topographical effect, he pointed out.

With his team at the ELZA Institute, he analysed corneal stroma from porcine eyes cross-linked at different fluences, from 15 joules/cm², up to 30 joules and even 60 joules. Considering cross-linking is made outside the eye, Dresden protocol 5.4 joules/cm² were not considered. The fastest protocol was used, with 30 mW for 16 minutes, 40 seconds. The results were published in the Journal of Refractive Surgery.¹

The second clear advantage of ECO-CAIRS is represented by hydration. The segment resists rehydration and stays super stiff for several minutes, Prof Hafezi noted.²

The modified procedure kills the keratocytes and stabilises the surface, making sure that no bacteria or living keratocytes remain on or within the segment. This drastically reduces risk of infection and rejection, giving the surgeon the possibility to cross-link and customise the segment at the same time in a less costly fashion.

Once treated, graft insertion is extremely fast, Prof Hafezi observed. By his fourth surgery, he implanted the graft in less than a minute due to the maintained stiffness and lack of resistance to the recipient stroma. To facilitate the insertion, he moistens one tip of the graft enough to grasp it with the forceps.

“It makes my blood pressure and my pulse low,” he said. The overall procedure takes 20 minutes in total.

This procedure can also be helpful for the whole procurement system. In countries where it is legal to use the same donor cornea for different recipients, it is possible to provide multiple patients with grafts using just one cornea, decreasing costs and increasing supply.

“From the same graft we can provide two patients with CAIRS implants,” Prof Hafezi said.

Dr Hafezi presented at the 2026 ESCRS Winter Meeting in Helsinki.

Farhad Hafezi MD, PhD, FARVO is Medical Director at the ELZA Institute of Zurich, Switzerland, and Professor at the Universities of Geneva (Switzerland), New York (US), Los Angeles (US), and Wenzhou (China). farhad@hafezi.ch

1. Aydemir ME, et al. Journal of Refractive Surgery, 2025; 41(11).

2. Kollros L, et al. submitted.