Under-flap stromal bed cross-linking shows promise in early post-LASIK ectasia
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Key takeaways:
- Under-flap stromal bed cross-linking is an effective strategy for early post-LASIK ectasia.
- A study showed positive outcomes in 20 eyes over 3 years of follow-up.
Post-LASIK ectasia, one of the most feared complications of LASIK, can be addressed early and efficiently by cross-linking the stromal bed under the LASIK flap.
“In the literature, post-LASIK ectasia has been shown to occur in 0.04% to 0.6% of cases. It is not a common complication, but it does happen, particularly for those surgeons who do a lot of surgery,” Avi Wallerstein, MD, FRCSC, told Healio.
Characteristic signs of this complication are stromal thinning, keratometric inferior steepening, progressive corneal irregularity and, ultimately, irregular corneal astigmatism.
“In other words, patients who went for regular refractive surgery with no other problem may end up with a disorder that has a heavy impact on vision and quality of life,” he said.
A safer alternative to epi-off
CXL has shown efficacy in halting the progression of surgically induced ectasia as well as keratoconus. However, the traditional epithelium-off procedure is not free from complications, such as persistent epithelial defects, infection, corneal scarring and recurrent erosion, as well as an extended recovery with pain and discomfort.
“We have to weigh the risks of epi-off CXL against progression of ectasia. Ophthalmologists are often hesitant to intervene right away and traditionally wait for progression. The problem is that the longer we wait, the more progression can occur. And with progression, you get more irregularity of the cornea and less chances of regaining good vision for these patients,” Wallerstein said.
Under-flap CXL (ufCXL) is an innovative procedure that is less invasive than epi-off and is worth performing in early cases of ectasia, when cornea biomechanics and vision are still minimally affected, with a small amount of irregular astigmatism.
“We did a study with early ectasia eyes. We included cases of new-onset ectasia, with cylinder not greater than 1.5 D, uncorrected distance vision of 20/40 or better, corrected distance vision of 20/25 or better, with new topographic irregular astigmatism and/or inferior steepening consistent with the diagnosis of post-LASIK ectasia,” he said.
Procedure and outcomes
The procedure begins by re-lifting the LASIK flap. By using an appropriate technique, reopening a flap is rarely a problem, even 10 to 15 years later, according to Wallerstein.
Once the flap is open at the laser bed microscope, a circular sponge soaked with 0.25% riboflavin is placed on the stromal bed, making sure not to touch the flap. After 5 minutes, the sponge is withdrawn, and the excess riboflavin is removed with a dry spear.
“Then you replace the flap as usual, with minimal irrigation, and verify it at the slit lamp. The next step is irradiating UV light on the surface of the cornea. I use an accelerated CXL protocol, 5 minutes, 18 mW/cm2, with a total energy of 5.4 J/cm2. During irradiation, a few lubricating drops are placed on the cornea. At the end of the procedure, you recheck the flap at the slit lamp to make sure it is in the right position with no striae, just as you normally would,” Wallerstein said.
With no riboflavin in the flap, only in stroma below it, the flap blocks only a minimal amount of UV light. The study eyes showed a demarcation line at an average depth of 336 µm from the corneal epithelial surface, which is the same depth reported after regular epi-off CXL with standard and accelerated protocols.
In the 20 eyes of 18 patients treated with ufCXL, all parameters improved or remained stable.
There was a nonsignificant increase in average sphere at 1 month, followed by a steady return to plano over the following 3 years. Mean cylinder steadily decreased from 0.83 D before ufCXL to 0.55 D at 3 years.
“As expected with CXL, central corneal thickness significantly decreased after the treatment but was back to baseline values after 12 months and remained stable over the 3 years of follow-up. Kmax significantly decreased in 16 eyes, three eyes had a marginal increase, and only one eye showed an increase of 1 D, which is a failure according to our criteria. However, that is a 5% failure rate, which is equivalent to what we see in regular cross-linking,” Wallerstein said. There were no complications, and all endothelial cell counts remained normal.
Of importance, none of the eyes underwent further visual rehabilitation. Many patients remained spectacle-free, and a few continued wearing their usual glasses and contact lenses. About half of the eyes had 20/20 vision, and 95% had 20/40. The safety index was unchanged.
Treat early
“These results are very encouraging. Although it is difficult to determine which cases of early post-LASIK ectasia progress and to what extent, we have a treatment that can halt progression with minimal risk to safety, visual downside or recovery. And you can do it early, as soon as the diagnosis is made, preventing the devastating consequences of progressing ectasia,” Wallerstein said.
Another potential advantage of early treatment is that a lesser amount of CXL is required to halt the progression of ectasia.
“I have encountered resistance within the ophthalmology community. Many are hesitant because they are used to waiting. But locking in the corneal changes at a stage when you have a minor impact on vision seems to me a much better strategy. I’d say do it early once the diagnosis is made — don’t wait for progression because it is late by then. If there is no risk, no visual downside and the procedure is safe, then there is a significant advantage to an early intervention. For those cases where it doesn’t halt the progression of ectasia, at that point, you can come back and do epi-off surface cross-linking,” Wallerstein said.
Wallerstein is the director of refractive surgery at McGill University and co-medical director of LASIK MD with 45 clinics across Canada and the United States, where about 70,000 procedures per year are performed by about 70 doctors.
“All of them are using the ufCXL technique now. So all these ectasia cases from the whole country are coming my way in terms of outcomes data. Overall, we can rely on more than 100, probably around 120 eyes, to widen the scope of our study. So, that’s exciting to have such data, and we’ll soon have more evidence to confirm that this treatment actually works,” he said.
References:
- Wallerstein A, et al. Clin Ophthalmol. 2016;doi:10.2147/OPTH.S118831.
- Wallerstein A, et al. J Cataract Refract Surg. 2023;doi:10.1097/j.jcrs.0000000000001162.
- Wallerstein A, et al. J Refract Surg. 2022;doi:10.3928/1081597X-20220713-01.
For more information:
Avi Wallerstein, MD, FRCSC, of LASIK MD, can be reached at awallerstein@lasikmd.com.
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