CXL a promising adjunct for hyperopic LASIK

Boston-Initial findings based on 2 years of follow-up in a randomized, fellow-eye controlled study indicate that adding cornea collagen crosslinking (CXL) routinely to LASIK for treatment of hyperopia or hyperopic astigmatism is safe and may stabilize the refractive outcome better compared with LASIK alone, according to Jonathan B. Kahn, MD.

The study included 27 patients with a mean follow-up of 23 months (range, 22 months to 35 months). Serial postoperative measurements showed a more stable keratometric curve over time in the eyes treated with CXL relative to that for the controls. Mean regression from treatment in the eyes that underwent the combined procedure (LASIK Xtra) was about 0.5 D less than in the controls (+0.22 D versus +0.72 D), reported Dr. Kahn.

Dr. Kahn was involved with the study as an ophthalmology resident, New York University School of Medicine, New York, where he collaborated with A. John Kanellopoulos, MD, clinical professor of ophthalmology, New York University School of Medicine, and director, Laservison.gr Institute, Athens, Greece. Dr. Kanellopoulos originated the idea of performing CXL at the time of LASIK as a strategy to limit long-term postoperative biomechanical changes. He has been performing the combined procedure in eyes undergoing LASIK for higher levels of myopic correction as a prophylactic measure to reduce the long-term risk of ectasia. However, it has not been well studied as a technique to stabilize the cornea after hyperopic LASIK, noted Dr. Kahn, who is currently a fellow in cornea/external diseases, Tufts New England Eye Center, Boston.

“We know that the refractive effect of hyperopic LASIK regresses over time, and several theories exist to explain this phenomenon,” Dr. Kahn explained. “One thought is that the regression represents latent hyperopia that may be masked by accommodative spasm. Another idea is that it is due to epithelial hypertrophy. However, the idea for performing CXL with LASIK is based on the theory that the long-term regression is related to an intrinsic biomechanical effect of the procedure that results in mid-peripheral steepening and central flattening. The results of this study are encouraging, but longer follow-up in a larger series is needed.”

The study population had a mean sphere of +3.25 D (range, +1.25 to +6.5 D) and mean cylinder of –1.75 D (range, plano to ­3.25 D). One eye was randomly assigned to undergo the combined procedure and the other to have LASIK alone.

Since patients with hyperopia have more significant angle kappa than those with myopia, LASIK was performed with a topography-guided ablation centered on the visual axis rather than the pupillary axis. Nasally decentered, 9.5-mm flaps were created with a femtosecond laser (FS200, Alcon) and the ablations done using the Allegretto 400 Hz Eye-Q excimer laser (Alcon).

After the flap was made, it was lifted and folded in a taco-like shape to avoid excess uptake of riboflavin solution into the flap. CXL is performed after the excimer laser ablation by instilling a single drop of extemporaneously compounded 0.1% sodium phosphate riboflavin solution (Leiter’s Pharmacy) and a drop of prednisolone acetate to help delineate the flap gutter. Once the flap is replaced, the eye is exposed to 1 minute of UVA light (KXL, Avedro) 30 mW/cm2. Intraoperative images presented by Dr. Kahn illustrated how the yellow riboflavin solution had soaked into the stroma under the flap. Postoperative OCT images showed areas of hyper-reflectivity where CXL had occurred at the stromal interface.

Dr. Kahn has no financial interest in the subject matter he discussed.  Dr. Kanellopoulos is a consultant to Avedro and Wavelight.