Ectasia After LASIK: Corvis TBI Screening and CAIRS Repair

Two things about ectasia after LASIK that I want every patient to know before we go any further.

The first is that I don’t do laser on corneas that can’t take it. Every candidate I see has the shape of their cornea mapped with Pentacam tomography and its strength measured with the Oculus Corvis ST, and the two results are combined into a single score, the TBI, that tells me whether the biomechanics are good enough. If they aren’t, we do something else.

The second is that ectasia which has already happened, usually after LASIK done elsewhere, can be repaired. Other surgeons send me these patients because the cornea can be stabilised with cross-linking and then reshaped with CAIRS keratoplasty, the donor-tissue ring procedure I’ve spent years performing and teaching.

Here’s how both of those work.

What ectasia after LASIK is

LASIK reshapes the cornea by lifting a thin flap and removing a calculated amount of tissue underneath it with an excimer laser. In the vast majority of eyes the cornea stays exactly as it was left. In a small number it doesn’t. It gradually weakens, thins, steepens and bulges forward, and vision that was crisp after surgery becomes blurred, doubled and hard to correct with glasses. That’s ectasia. It looks very much like keratoconus, and across large published series it affects roughly 0.04% to 0.6% of eyes treated with LASIK.

The important point is what ectasia actually is: a failure of corneal strength. A cornea that develops ectasia after LASIK was almost always weaker than it looked beforehand. The laser didn’t create the weakness, it removed the margin that was hiding it. So the whole question of ectasia comes down to one thing, which is measuring corneal strength before anyone operates.

Why looking at the shape alone isn’t enough

For a long time, screening meant looking at the shape of the cornea. The most widely used risk model, published by Randleman and colleagues in 2008, scores abnormal topography, how much cornea will be left beneath the flap, age, corneal thickness and the size of the prescription, and abnormal topography is the strongest single warning sign in it.

Shape-based screening catches most at-risk corneas, but not all of them. Some eyes that go on to develop ectasia have topography that looks entirely normal before surgery. Their weakness is real, it just hasn’t changed the shape yet. To find those corneas you have to measure strength directly, not infer it from shape.

How I screen: Pentacam tomography plus Corvis biomechanics

Every laser candidate I see has two scans.

Pentacam tomography maps the front and back surface of the cornea and its thickness at thousands of points. I’ve written before about how tomography changed the way we detect early keratoconus. This is the shape half of the picture.

Corvis ST biomechanics is the strength half. The Corvis ST, made by Oculus in Germany, releases a precisely metered puff of air at the cornea and films it bending inward and springing back with a high-speed Scheimpflug camera running at 4,330 frames per second. From that footage it measures how far the cornea deforms, how fast, and how it recovers. A weak cornea bends further and behaves differently from a strong one, even when the two look identical on a shape map.

The TBI score brings the two together. The Tomographic Biomechanical Index was developed by Renato Ambrósio and colleagues, who used machine learning to combine the Pentacam and Corvis ST data into a single number between 0 and 1. In the study that introduced it, the TBI separated ectatic from normal corneas with an area under the curve of 0.996, better than tomography alone at 0.956 or biomechanics alone at 0.936. More importantly for LASIK screening, it was built and tested on the hardest cases: the normal-looking eyes of patients whose other eye had ectasia, exactly the corneas that shape-based screening misses.

If the TBI and the rest of the assessment tell me a cornea is biomechanically marginal, I won’t do LASIK on it, and I’ll tell you why. That might mean a different procedure, a lens-based option such as an implantable lens or refractive lens exchange, or no surgery at all. I’d far rather turn down a laser procedure than manage an ectasia I caused.

No screening test is perfect, and I don’t pretend this one is. But combining shape and strength is the best method we have for making sure a cornea can take the treatment. If you’re considering laser surgery anywhere, the question worth asking is not whether ectasia is possible but “how have you measured my corneal biomechanics?” If the answer is a topography map alone, that’s worth knowing.

When ectasia has already happened: repairing it with CAIRS

A good proportion of the post-LASIK ectasia I treat developed after surgery performed elsewhere, and many of those patients are sent to me by their original surgeon or another ophthalmologist. That referral pathway exists because the shape of an ectatic cornea can now be rebuilt, and the treatment has two steps, in order.

First, stop it getting worse

If the scans show the cornea is still changing, corneal cross-linking stabilises it. Riboflavin and ultraviolet light create new bonds between the collagen fibres, stiffening the cornea. In the US multicentre trial that led to FDA approval of cross-linking for ectasia after refractive surgery, treated corneas flattened slightly over the first year while untreated corneas kept steepening. I use epithelium-on cross-linking with the Glaukos Mosaic system, which means a quick recovery and a treatment pattern that can be customised to the cornea’s shape.

Cross-linking stabilises. It doesn’t reshape. That’s the next step.

Then, rebuild the shape with CAIRS

CAIRS, corneal allogenic intrastromal ring segments, are arcs of donor corneal tissue placed into channels cut in the cornea with a femtosecond laser. They push the bulging cornea back toward a regular curve, reducing the steepness and the irregular astigmatism that glasses can’t correct. Because the segments are human corneal tissue rather than plastic, they avoid the complications that led synthetic rings such as Intacs to fall out of favour, and CAIRS is performed as a keratoplasty procedure that Medicare recognises. I’ve compared the two approaches in CAIRS vs Intacs and Kerarings.

CAIRS was developed for keratoconus, and that’s still most of what I use it for. Its use in post-LASIK ectasia is newer, and the evidence is growing. A 2025 series in the Journal of Refractive Surgery combining customised CAIRS with cross-linking for post-LASIK ectasia reported improvement in both uncorrected and best-corrected vision, with reduced corneal steepness and coma, and no major complications. That matches what I see in my own patients. Planning the segments for a post-LASIK cornea is a customisation exercise, which is what CAIRSplan, the planning tool I co-developed, is for, and it’s part of what I cover when teaching CAIRS to surgeons internationally.

Once the cornea is stable and more regular, whatever prescription remains is handled with glasses or contact lenses, and for some patients a scleral lens over a reshaped cornea is the combination that gets them back to driving comfortably. You can read about what recovery looks like week by week, how long CAIRS lasts and being asleep for CAIRS surgery.

Will I need a corneal transplant?

Usually not. Corneal transplantation remains the answer for advanced ectasia with significant scarring, or a cornea too thin for anything else, but it sits at the far end of the pathway. Cross-linking to stabilise, CAIRS to reshape and modern lenses to fine-tune mean most patients never get there.

For referring surgeons and optometrists

If you have a patient with ectasia after LASIK, I’m happy to see them. Send the current tomography, any earlier scans, and the original treatment record if it’s available, since the flap thickness and ablation depth help with planning. Details are on the referrers page.

The bottom line

Ectasia after LASIK is a strength problem at both ends. Before surgery, the answer is to measure corneal strength properly and not to laser a weak cornea, which is what Pentacam, Corvis and the TBI score are for. After it, if it has already happened, the answer is cross-linking to stabilise the cornea and CAIRS to rebuild its shape. Both are available here.

If you’ve noticed worsening vision, increasing astigmatism, ghosting or glare after LASIK, or you want your corneal biomechanics measured before you have it, book a consultation.