Strengthening corneas in Singapore
by Matt Young EyeWorld Contributing Writer
Surgeon explains why and how he performs crosslinking during many LASIK procedures
While there are known risk factors for ectasia after LASIK, analysis of such factors continues to remain controversial. Scoring systems can lead to incorrect predictions of risk factors that-let's face it-still aren't entirely understood.
Even as surgeons attempt to screen out bad LASIK candidates from good ones, corneal crosslinking is-in some countries-allowing surgeons to stabilize many more corneas during the LASIK procedure.
At least that's what Jerry Tan, F.R.C.S., believes.
Dr. Tan, consultant eye surgeon, Jerry Tan Eye Surgery, Singapore, has been performing follow-up for patients who have undergone corneal crosslinking during LASIK for the last nine months.
He is among a select group of surgeons performing this procedure outside of the U.S., where the procedure has yet to gain approval from the FDA.
Dr. Tan performs Lasik Xtra (Avedro, Waltham, Mass.), which involves corneal crosslinking, on corneas potentially at risk for ectasia, on hyperopic LASIK patients as well as on very high myopes.
"At present, there is no major complication we see," Dr. Tan said. Dr. Tan explained step by step how the procedure compares to a normal LASIK procedure and his reasons for taking such steps toward more stable corneas and ones that do not regress visually.
Risks vs. benefits
Despite practicing Lasik Xtra over the course of the past year, Dr. Tan readily admits that the body of scientific literature supporting the procedure could be stronger. "At the present moment, there are few papers that have been written on Lasik Xtra regarding hyperopia," Dr. Tan said. Several peer-review articles have favorably discussed Lasik Xtra for high myopia, many just appearing in the later half of 2012. Meanwhile, discussion of Lasik Xtra for hyperopia appears more prevalently not in peer-reviewed literature, but at ophthalmic meetings and in trade articles. That said, in Dr. Tan's hands, the procedure seems to be working well for hyperopic patients.
"Nobody knows why hyperopic LASIK seems to be more stable [with Lasik Xtra]," Dr. Tan said.
"The cornea profile seems to be better."
For its part, Avedro says that Lasik Xtra preserves "corneal biomechanical integrity" in company literature. Essentially, a riboflavin formula is applied to the cornea during LASIK along with UVA illumination in order to bring about crosslinking with the intention of strengthening the cornea. Using topography, Dr. Tan said these hyperopic corneas post-surgery with Lasik Xtra look better-i.e., "shapes are beautiful"-compared to non-Lasik Xtra procedures. He also feels there is less regression occurring among Lasik Xtra cases-a notorious occurrence among standard hyperopic LASIK cases. High myopes also tend to experience significant regression after LASIK, but not with Lasik Xtra, Dr. Tan said. In fact, while standard LASIK patients experience a "wow" factor almost immediately post-op, that effect tends to diminish with regression over the course of weeks and months in high myopes. With Lasik Xtra, it's just the opposite, Dr. Tan said. A small amount of myopia tends to remain immediately post-op, and vision continues to improve to plano until about the three-month follow-up period, he said. "The patients tell me they see better and better," Dr. Tan said. "So I am getting late-onset ‘wows.'"
Dr. Tan much prefers late-onset "wows" to regression, and so do his patients, he said. Patients potentially at risk for ectasia (i.e., young patients, those with thinner corneas, etc.) also appreciate the added potential safety that crosslinking allows.
In my hands
Normally, corneal ectasia develops anywhere from two to four years after LASIK and even as late as 10 years post-op, Dr. Tan said. "This is something very difficult to predict in normal eyes," Dr. Tan said. "So I do [Lasik Xtra] on all high myopes, and all patients who have a residual corneal thickness of 250-300 microns in the stromal bed underneath the flap. I tell the patient, ‘I think you need Lasik Xtra just in case I make the cornea too weak.' Most of them say, ‘If it's no risk to me, I just get a bit of insurance.'" As noted earlier, Dr. Tan also performs Lasik Xtra on hyperopes. Normally, Dr. Tan starts out the LASIK procedure with IntraLase (Abbott Medical Optics, Santa Ana, Calif.). He makes a 100-110 micron flap. Dr. Tan applies the riboflavin (without dextran) for 45 seconds to the stroma, rinsing any excess from the flap. Then he puts the flap back. Dr. Tan applies UV light (30 mW/cm2) to the cornea for 45 seconds. Afterward, he waits an additional minute. That's it. These are the only procedural differences compared to standard LASIK. For Dr. Tan, this means no additional time to the LASIK procedure required. Normally when Dr. Tan doesn't perform Lasik Xtra, after putting the flap back, he waits three minutes and then finishes the procedure. "I like to wait three minutes for my flap to really stick on well so there are no flap shifts [during standard LASIK]," Dr. Tan said. "I used to wait one minute but then would occasionally get a few flap shifts. Then I waited two minutes and rarely would get flap shifts. When I wait three minutes I get no flap shifts. For the last few thousand cases I have never had a flap shift. So I wait three minutes. It seems to be a nice magic figure for me."
Now instead of waiting three minutes, he performs the crosslinking component during this time. With the riboflavin component, UVA illumination component, and added machines moving about during crosslinking, the time involved is identical to Dr. Tan's standard LASIK procedure. "It doesn't increase my time for surgery at all, at least for my technique," Dr. Tan said.
Drawbacks vs. drawbacks
Initially, Dr. Tan said he was using a riboflavin formula that included dextran during the Lasik Xtra procedure. "When you leave dextran underneath the flap, it causes a little bit of DLK," Dr. Tan said. "With the new formulation of riboflavin without dextran-with just normal saline-there is no DLK." The DLK experienced previously was mild, grade 1 DLK, he said. While the jury is still out on the long-term effects of crosslinking, Dr. Tan is convinced that it is safer than performing PRK with mitomycin-C, another refractive surgery option for higher myopia that reduces the risk of ectasia. "If you have a choice between crosslinking and mitomycin-C, mitomycin-C is more dangerous," he said. Meanwhile, Lasik Xtra is a better option than the Visian ICL (STAAR Surgical, Monrovia, Calif.) for many cases in Singapore, he said. Dr. Tan described the typical Singaporean myope as having "long eyeballs and anterior chambers that are too shallow for the Visian ICL. If I try to [implant a Visian ICL] in Singapore, the anterior chamber is going to be too small." Referring to Lasik Xtra, Dr. Tan said, "If there is no downside, why not do it?"
Editors' note: Dr. Tan has no financial interests related to this article.
Source: EyeWorld January 2013