CAIRS vs Intacs and Kerarings: Donor Tissue or Plastic?

If you’ve been reading about keratoconus surgery, you’ll have come across three names for what sounds like the same idea: Intacs, Kerarings and CAIRS. All three are curved segments placed inside the cornea to flatten the cone. So patients reasonably ask me which is best, and whether it matters.

It matters. The mechanical principle is shared, but the material is not, and in a thin, weak keratoconic cornea the material is most of the story. There’s also a practical difference that surprises people: in Australia, CAIRS is covered by Medicare as a keratoplasty, and Intacs and Kerarings are not.

What Intacs and Kerarings are

Synthetic ring segments have been around since the 1990s. Intacs were originally approved to correct short-sightedness in normal corneas, and in 2004 the US Food and Drug Administration granted a humanitarian device exemption allowing their use in keratoconus. They’re made of PMMA, a rigid acrylic plastic, with a hexagonal cross-section, and they sit at roughly 70 to 80 per cent depth in the cornea. Kerarings, along with the Ferrara ring and the MyoRing, belong to the same family: different shapes and arc lengths, the same plastic.

They work. Plenty of people have had good results from synthetic segments over the last thirty years, and I’m not going to pretend otherwise. The problem isn’t whether they can flatten a cone. It’s what plastic does inside a cornea over time.

What CAIRS is

CAIRS stands for corneal allogenic intrastromal ring segments. Instead of plastic, the segment is cut from donor corneal tissue, the same collagen your own cornea is made of, and placed into a channel cut by a femtosecond laser. The added volume flattens and regularises the cone in the same way a synthetic ring would. The technique was first described by Dr Soosan Jacob in India, with the first published series appearing in 2018, and Dr David Gunn and I brought it to Australia.

As we put it on CAIRSPlan, the planning platform Dr Gunn and I built for surgeons: a biological implant may reduce the risk of the extrusion and stromal thinning seen with PMMA segments, and the segments can be exchanged or removed straightforwardly down the track if the corneal shape evolves. That’s our own description, so treat it as the view of two surgeons who do a lot of this. The published evidence below is where the weight sits.

The problem with plastic in a thin cornea

A keratoconic cornea is thin, and it’s weakest exactly where you want the ring to sit. A rigid foreign object in that tissue has a set of well-documented failure modes: the segment can migrate, the cornea can thin and melt over it, new blood vessels can grow in towards it, and in the worst case the ring works its way out through the surface, which is called extrusion.

How often? It depends on the series. A large multicentre study found that 5.6 per cent of synthetic segments were explanted, and a 2025 review of the literature reports removal rates ranging from about one per cent to as high as 30 per cent depending on the study and the ring. Those are not rare-event numbers. For a procedure done on young people who will live with the result for fifty years, a one-in-twenty chance of needing the implant taken out again is a real consideration.

None of this is a mechanism CAIRS has. Donor stroma doesn’t melt the cornea around it or migrate through it, because it is cornea. The segment integrates and stays put. I’ve written separately about what the long-term CAIRS data looks like a decade on.

What the head-to-head evidence says

CAIRS is the newer procedure, so its evidence base is younger, and I’d rather say that plainly than oversell it.

The first direct comparison was published in 2024: a propensity-matched study that paired CAIRS eyes with Intacs eyes of similar age, cone steepness, corneal thickness and segment size. Both groups improved significantly in corrected vision, astigmatism and corneal curvature. Where they differed was in how many eyes gained two or more lines of best-corrected vision, which favoured CAIRS.

A 2025 systematic review and meta-analysis pooling the CAIRS literature found the steepest corneal reading fell on average from about 58 to 53.5 dioptres, roughly 85 per cent of eyes improved their uncorrected vision, and no major complications were reported across the included studies. Those results will mature as the follow-up lengthens, but they’re consistent with what we see in Brisbane.

Made to measure, not off the shelf

Synthetic segments come in a catalogue. You choose the closest size and arc from what the manufacturer makes. CAIRS is cut to the cornea in front of you: the length, thickness and position of each segment are chosen for that particular cone, and customised segments for off-centre cones are part of the published technique.

That freedom is only useful if you know what to cut. It’s the reason Dr Gunn and I published the Brisbane nomogram, a planning system derived from 85 keratoconic eyes, and built it into CAIRSPlan so that any surgeon can plan a case to the same standard. The platform has just been rebuilt from the ground up with a new geometry engine and an automated planner, and it remains free. I’m biased about it, obviously, but the planning is where predictable results come from.

If you’ve already got synthetic rings

A question I’m asked more and more: what if I’ve already had Intacs or Kerarings and they’ve caused trouble? The answer is encouraging. Removing a failed synthetic segment and replacing it with CAIRS has been described in the literature as a rescue procedure for exactly this situation, and it’s something I do. The plastic comes out, the channel heals, and donor tissue goes in.

What neither procedure does

Neither Intacs, Kerarings nor CAIRS stops keratoconus progressing. They reshape the cornea to improve vision. Halting the disease is the job of corneal cross-linking, and where the cone is still moving we do both. Anyone promising that a ring alone will “cure” keratoconus is overselling it, whichever material they use.

The cost difference in Australia

This is the part that tends to settle the decision for Australian patients. Since November 2025, Medicare has recognised CAIRS as a keratoplasty under item number 42653. That means a Medicare rebate on the surgery, and it means private health insurers must cover it under the appropriate level of hospital cover. Intacs and Kerarings have no Medicare item number at all. They are refractive devices in the eyes of the system, and the entire cost is borne by the patient.

So for the same mechanical goal, one option comes with a rebate and hospital cover, and the other is fully out of pocket. Combined with the complication profile above, it’s hard to make the case for plastic.

The bottom line

Intacs and Kerarings were a genuine advance when they arrived, and they helped a lot of people. But they put a rigid foreign body into the weakest part of a weak cornea, and the removal rates in the literature reflect that. CAIRS does the same job with your cornea’s own material, can be cut to fit, can be exchanged if needed, and in Australia is the only one of the three that Medicare recognises.

If you’re weighing up the options, the CAIRS treatment page covers the procedure itself, the recovery guide covers the weeks afterwards, and CAIRS vs CTAK compares the two donor-tissue approaches. Book a consultation and bring your corneal maps; the right answer for your eye is in them.