CXL with primary LASIK at crossroads
There is no current justification for considering routine corneal crosslinking for primary prevention of postLASIK ectasia-considering the many unknowns about the efficacy and safety of combining procedures-relates one ophthalmologist.
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There is no current justification for considering routine corneal crosslinking for primary prevention of postLASIK ectasia-considering the many unknowns about the efficacy and safety of combining procedures-relates one ophthalmologist.
By Cheryl Guttman Krader; Reviewed by Perry S. Binder, MS, MD
Irvine, CA-An assessment of current knowledge on the potential risks and benefits of performing corneal crosslinking (CXL) at the time of primary LASIK indicates there is no current justification for routine application of the combined procedure, according to Perry S. Binder, MS, MD.
“The idea of performing CXL on every LASIK case is based on the hope of preventing ectasia,” said Dr. Binder, clinical professor of ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine. “However, peer-reviewed studies of CXL at the time of primary LASIK are very limited, and there are alternatives to LASIK that can be used successfully in cases deemed at risk for ectasia.”
“In addition, I don’t believe we can defend the increased cost of CXL to patients in lieu of what we know about the current risk/incidence of ectasia,” Dr. Binder added. “Therefore, my recommendation is that CXL should not be performed at the time of LASIK until research is published or presented that tips the risk:benefit ratio in favor of the combined procedure.”
Outlining his arguments against performing primary CXL to prevent postLASIK ectasia, Dr. Binder highlighted the current low risk for that complication and explained the underlying factors.
“Improved surgeon awareness has resulted in better screening efforts,” he said.
In addition, we have better methods for screening, more reliable technology for achieving predictable flap thickness, and more ways to measure postoperative flap and residual stromal bed thickness, according to Dr. Binder.
Performing CXL routinely can add risks, particularly corneal ulcers, corneal infiltrates, risks associated with epithelial removal, and corneal endothelial damage, he noted.
In addition, there are a variety of unknowns accompanying simultaneous CXL-LASIK.
Unanswered questions
One of the most basic questions that must be answered is whether CXL at the time of primary LASIK is effective in preventing ectasia.
With all of the clinical variables that would need to be accounted for in stratifying treatment groups, a study would need to enroll a minimum of 300 to 400 eyes to detect a benefit of CXL for reducing the risk of ectasia after primary LASIK, Dr. Binder noted.
Considering the multiple differences between CXL performed with LASIK versus using the standard Dresden protocol that is used to treat keratoconus provides reason to question the safety and efficacy of combining CXL with LASIK.
“We don’t know how riboflavin or UVA penetration into the cornea is affected by a healthy LASIK epithelium or how riboflavin diffuses from the LASIK interface in either direction,” Dr. Binder said. “In addition, it is not known how CXL might affect primary and enhancement excimer laser ablation rates or the stability of refraction postLASIK.
“How would one determine the contribution of CXL versus routine wound healing to the outcomes, and knowing that the effects of CXL can continue for many years, when would it be appropriate to perform an enhancement procedure?” he asked.
Other questions remaining to be answered include whether the CXL procedure might affect LASIK flap adhesion, have long-term adverse effects on the crystalline lens, or affect calculations for subsequent pseudophakic IOL implantation.
In addition to the need for studies addressing these many issues to understand the risks and benefits of the combination procedure, Dr. Binder called for research toward improving the predictability, efficacy, and safety of CXL.
A variety of CXL protocols are being used without any laboratory data or clinical studies to support their efficacy or safety, he explained.
In addition, more information is needed to establish the best method for riboflavin delivery, and investigations of other photosensitizers would also be worthwhile.
Considering the potential for UVA toxicity to the conjunctiva, corneal stem cells, and corneal endothelium, there is also a need to develop systems for delivering focal irradiation to the affected cornea and for more accurately determining the depth of treatment and its effects on corneal biomechanics, Dr. Binder noted.
Perry S. Binder, MS, MD
Dr. Binder has no relevant financial interests to disclose.
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