Would you consider PRK as a re-treatment after LASIK?
In most cases, as it is the safest option
Yes, I would, especially if the residual bed is thin, the original operation has been deep and the corneal nerves have had a few years to recover before the reoperation.
A multiple procedure such as flap lift, in addition to thin preoperative cornea, thin residual bed and deep photoablation, is one of the risks for iatrogenic keratectasia. Because the flap contributes minimally to the mechanical integrity of the post-LASIK cornea, a PRK approach is safer in my view.
Although no official data are available, I would recommend setting the re-treatment ablation depth within the limits of one-third of the stromal thickness of the LASIK flap.
The risk of haze, which is notoriously a drawback of the surface re-treatment approach, appears to be higher if PRK is performed soon after LASIK. This can probably be avoided, or at least minimized, by using topical mitomycin C, but I have no personal experience with it in this context. All my cases were re-treated 2 years to 4 years after primary LASIK, and only some of the eyes I have treated developed mild haze, which disappeared before the last postoperative follow-up.
Transepithelial PRK, which I perform regularly, offers further advantages, as it smoothens the subepithelial Bowmans ridges that are often observed in even normal-looking post-LASIK corneas after epithelial debridement. The flap edges are not a problem with this method. An exceptionally thick epithelium may be a problem if not controlled. The patient may end up having no ablation at all.
Surface ablation also works relatively well in some special cases, such as a small buttonhole or a slightly deformed flap and post-RK hyperopia, which is unsuitable for LASIK.
The drawbacks are classic: some pain, need for postoperative steroids, longer follow-up and slightly slower healing. There are no major medical problems, but the surgeon must be prepared to devote additional chair time to listening to the patients complaints and encouraging him or her.
Timo Tervo, MD, can be reached at the University of Helsinki, Finland. Disclosure: Dr. Tervo has no relevant financial disclosures.
Only in a few specific cases, due to risk of haze
Whenever we re-treat LASIK, we should first answer a few preliminary questions: What kind of corneal profile are we dealing with? How much tissue is available in the corneal bed and in the flap? What type of ablation should we set?
Re-LASIK is better avoided.
Flap lift has a 6% to 8% risk rate of interface epithelialization and a high rate of symptomatic dry eye. The risk is lower (2%) with femto-LASIK, thanks to the geometry of the incision. However, ultrathin femtolaser flaps with a complex edge geometry might be difficult to relift due to the tight adhesion of the margin and difficult to reposition without causing flap striae. By reducing scleral bed thickness, both re-LASIK and flap lift increase the risk of ectasia. However, if the primitive profile has a small, cone-shaped optical zone, I use a topo-aberrometry-based treatment to enlarge it. In this way, I achieve a better stabilization of corneal biomechanics, reducing the risk of ectasia despite the reduced stromal thickness.
Doing PRK on the flap is easier but carries a risk of haze degree 2 to 3 up to 15%. By using transepithelial custom ablation, or LASEK, with MMC, the risk of haze can be reduced, but not in all the cases. The increased chance of developing haze is due to the alteration of the sub-Bowmans nerve plexus induced by the primary procedure.
To conclude: If there is sufficient tissue (more than 300 µm) and a large enough stromal bed, I prefer lifting the flap. The margin is normally easy to find by simple slit-lamp observation. If I do not have so much tissue available on the stromal bed, but a regular flap, thick and without striae, I may consider transepithelial PRK or LASEK with MMC. In all these cases, I use customized topo-aberrometry-based ablation.
Ugo Cimberle, MD, can be reached at the Center of Ocular Microsurgery, Ravenna, Italy. Disclosure: Dr. Cimberle has no relevant financial disclosures.