In 2012, as a cornea specialist in the United States, it was difficult to know what to do for my keratoconus patients. I saw many patients with mild to moderate keratoconus who were in their teens and 20s and needed corneal collagen crosslinking (CXL). However, the nearest CXL surgeon was hours away, and the procedure was not yet approved by the FDA.
Unfortunately, many patients simply did not bother with CXL, and their keratoconus continued to worsen. So, I decided it was time to start performing CXL for my patients. I studied the evidence behind CXL and the various techniques, discussed the finer details with experienced surgeons, and attended various CXL meetings.
Immediately, it became obvious to me that the transepithelial approach would be my preferred technique. At the time, publications on this approach were sparse, but the data available were promising. Transepithelial CXL is undeniably safer than the traditional epithelium-off (epi-off) approach. Removal of the epithelium inevitably leads to increased risk of corneal haze, infection, non-healing defects, and scars, whereas transepithelial CXL carries none of these risks.
The only question up for debate then is how effective is transepithelial CXL? After performing the procedure for 4 years now, I believe that transepithelial CXL is just as effective as epi-off CXL. At 1 year postoperative, 91% of 65 eyes remained stable by topography, and maximum keratometry flattened an average of 0.63 D. These results are right in line with data from studies of the epi-off technique. Plus, no eyes experienced corneal haze, infection, non-healing defects, or scars.
This past April, the FDA approved the use of CXL for keratoconus in the United States. Now that CXL has been accepted as a legitimate treatment for stabilizing keratoconus, where do we go from here? Investigators are currently working to improve the technique, apply CXL to other eye diseases, and combine the procedure with other treatments. In traditional protocols, the eye is exposed to ultraviolet light for 30 minutes, but early clinical results for exposure times as short as 3 minutes have been promising. LASIK Xtra (Avedro) has been proposed as a way to “lock in” a refraction and guard against ectasia while performing LASIK. An abbreviated CXL protocol with lower energy and shorter duration is performed at the time of LASIK. With this weaker ultraviolet light exposure, it is unclear how much LASIK Xtra actually stiffens the cornea. More studies are needed.
Traditional CXL can cause corneal flattening for as long as 4 years, so I worry that a LASIK patient’s refractive status may be unstable when combined with prophylactic CXL. On the other hand, topography-guided PRK combined with CXL has real promise. CXL stiffens and strengthens the cornea, allowing a patient with keratoconus to undergo topography-guided PRK. In some cases, results have been very good. Keratoconus patients who are unable to tolerate hard contact lenses and have poor vision with glasses may have a new alternative for visual improvement.
