October 2012

 

REFRACTIVE SURGERY

 

Deciphering femtosecond-related DLK


by Maxine Lipner Senior EyeWorld Contributing Writer

   
Cornea with DLK in eye

Cornea with DLK in eye that underwent femtosecond LASIK flap cut Source: Roni M. Shtein, M.D. (from the original JCRS article)

How this is affecting laser-cut flaps

The higher the energy setting and the larger the flap created with a femtosecond laser, the more likely for diffuse lamellar keratitis (DLK) to occur, study results published in the June issue of the Journal of Cataract & Refractive Surgery suggest.1 Yet many of these cases tend to be mild, according to Roni M. Shtein, M.D., assistant professor of ophthalmology, University of Michigan, Ann Arbor, who took part in the investigation.

Included in the study were 801 eyes that had undergone myopic LASIK with flap creation done by the IntraLase (Abbott Medical Optics, Santa Ana, Calif.) 60 KHz femtosecond laser. Of these cases, 12.4% went on to develop DLK. Dr. Shtein attributes the relatively high number to how DLK was defined, which in this case included even mild flap interface inflammation treated with a routine anti-inflammatory regimen. DLK is typically characterized by a sterile, diffuse white infiltrate seen within the first week after LASIK. While this can be very mild and localized to the interface between the flap and the stroma, on the other end of the spectrum, DLK can result in stromal necrosis and flap melting.

Mild transient DLK

Mild transient DLK usually resolves easily without any additional intervention beyond what is given after LASIK, almost making it unnecessary to call it DLK, according to Dr. Shtein. "We routinely have our LASIK patients on topical steroid eye drops for a week after surgery," she said. "If the inflammation has resolved without any additional steroid, we still record it as DLK because it is inflammation."

Dr. Shtein theorizes that damage to the cornea, caused by higher energy settings used to make the flap, may be to blame for DLK here. "There have been some laboratory studies that have shown more inflammation with higher energy settings of the laser," she said. "I think that is probably the case [where] there is collateral damage." This damage may, in fact, be very minor. "There's not a lot with the femtosecond, but if you're using higher energy level settings than is necessary, you're probably inciting a little bit of inflammation."

In mild transient DLK this may not necessarily be a bad thing. "It may be leading to a stronger healing of the flap," Dr. Shtein said. "So this mild level of DLK, I don't think that I would want to induce it, but I am not too concerned about it."

Associated factors

When study investigators narrowed down the definition of DLK to those who required additional intervention, they discovered more significant cases. "When we focus on those who were treated with more than standard treatment, who were treated with steroids for longer than 1 week, the rate of DLK was 2 or 3%, which is more consistent with the rates in the literature," Dr. Shtein said. Investigators found that some of the factors that seemed to increase incidence of DLK included a larger flap diameter, higher raster energy, and higher sidecut energy. "We did find that the laser settings correlated so that the more energy we used, the more often we saw inflammation," Dr. Shtein said. "The other finding we saw was that with larger flap diameters [there was] more inflammation."

Dr. Shtein thinks this goes back to the basic science of where the inflammation comes from. "It's likely coming from the limbal blood vessels, and the inflammatory cells are able to reach the flap more easily if it's a larger flap," she said. Even given this, large flaps are not necessarily something to be avoided. "There are a lot of benefits to having larger flap sizes in terms of optical properties of the surgery," she said. "But it teaches us a little bit more about the pathophysiology of [DLK]."

Treatment for femtosecond DLK, like with mechanical microkeratomes, centers on steroid anti- inflammatory medication. In mild cases, Dr. Shtein finds that a topical steroid often will suffice. "As it gets more severe, occasionally patients will be treated with oral steroids and frequent topical steroids," she said. "If it gets to a severe enough degree, sometimes the flap is lifted to debulk some of the inflammation by scrapping the bed."

Overall, Dr. Shtein sees the study as helping to elucidate how the femtosecond laser is different from the mechanical microkeratome in the response of the cornea. "I think that it highlights the fact that although there is more DLK after femtosecond LASIK, it tends to be very mild and not clinically significant, and we understand more about what factors we can modify and manipulate to minimize the chance of DLK," she said. "It doesn't necessarily mean that we have to modify our technique, but at least we know what factors to take into account." As far as energy settings with the femtosecond laser, Dr. Shtein pointed out that it's a question of weighing key factors. "You don't want to lower your energy settings to the point where it's difficult to lift the flap. You're going to cause more trauma and more damage," she said. "It's a question of finding the balance between these controllable parameters."

Reference

1. de Paula FH, Khairallah CG, Niziol LM, et al. J Cataract Refract Surg. 2012;38:1009-1014.

Editors' note: Dr. Shtein has no financial interests related to this article.

Contact information

Shtein: 734-763-5506, ronim@med.umich.edu

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