Take-home: Patients with thin corneas as the result of keratoconus, ectasia following LASIK, or pellucid marginal degeneration can safely undergo epithelial-on collagen crosslinking with pulsed UV light and achieve visual benefits from the procedure.
Reviewed by William Trattler, MD
Miami—Patients with thin corneas as the result of keratoconus, ectasia following LASIK, or pellucid marginal degeneration can safely undergo epithelial-on collagen crosslinking (Epi-on CXL) with pulsed ultraviolet (UV) light and achieve visual benefits from the procedure, according to William Trattler, MD.
CXL has been shown to stop progression of keratoconus and stabilize the corneal shape in a high percentage of patients. CXL can also improve both the uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA) levels in many patients with ectatic corneal disease.
The FDA approved Epi-off CXL on April 18, 2016, based on numerous trials of the technology in the United States and internationally. However, while Epi-off CXL has a long track record with positive outcomes, there is still room to advance the CXL treatment. One area of focus is optimizing the delivery of riboflavin so the epithelium does not need to be removed. Other areas of focus include increases in UV energy, which can allow for shorter treatment times, as well as pulsing of the UV light. Overall, the current FDA-approved CXL technology works well for patients with keratoconus and post-LASIK ectasia, but there is room for further innovations, Dr. Trattler said.
Keratoconus progression: the treatment debate
Dr. Trattler, who is from the Center for Excellence in Eye Care, Miami, pointed out keratoconus can progress at any age and progression results in worsening of the patient’s refractive error and loss of BCVA. Even patients who have undergone implantation of corneal implants (Intacs, Addition Technology) and corneal transplants can experience progression of their keratoconus. Interestingly, in Europe, where the epithelial-off procedure is performed, the standard practice is to wait for keratoconus to progress in adults before undertaking CXL.
However, waiting may not be in the best interests of the patients, Dr. Trattler said. He shared a number of cases where keratoconus progressed markedly in as little as 3 months. In one case, for example, progression of keratoconus in a 63-year-old woman resulted in an increase in K values of + 4.4 D over a period of 4 years and 2 months.
With the risk for progression being present for all keratoconus patients, one should consider crosslinking once a patient is diagnosed with keratoconus. Surgeons can expect that for many patients, crosslinking will not only stabilize the cornea, but will in fact lead to improvement in corneal shape and vision, he said. Dr. Trattler described the outcome in a 35-year-old woman treated with Epi-on CXL who, at 26 months postoperatively, had an improvement in Kmax values from 60.1 to 54.3 D, i.e., - 5.8 D.
Following Epi-off CXL, the rate of progression after treatment was found to be about 3%, as reported recently by Antoun et al. in the Journal of Ophthalmology (2015; http://dx.doi.org/10.1155/2015/690961). If patients progress following CXL, one can repeat the CXL procedure, expecting the second procedure to typically be succesful at stabilizing the corneal shape.Epi-on CXL
Transepithelial CXL (also known as Epi-on CXL) differs from the Epi-off procedure in that the epithelium is left undisturbed, leading to a more rapid healing time. A bandage contact lens is needed. However, a longer riboflavin loading time may be required to reach the desired end point.
In Dr. Trattler’s experience as part of a clinical trial sponsored by CXLUSA, administration of an optimized riboflavin with a delivery system resting on the corneal epithelium can result in sufficient riboflavin within the corneal stroma. The loading time can be as fast as 20 to 30 minutes. Work with other riboflavin formulations designed for Epi-on could take 1 or more hours to load. One important caveat is a required slit-lamp examination to verify the corneal stroma has sufficient riboflavin present prior to initiating the UV light.
Dr. Trattler and colleagues conducted a study of Epi-on CXL to determine the procedure’s efficacy in patients with keratoconus, post-LASIK ectasia, and pellucid marginal degeneration and thin corneas ( < 450 µm) who had undergone the treatment either unilaterally or bilaterally with a pulsed light exposure time of 30 minutes. The patients evaluated were enrolled in the CXLUSA multicenter trial with sites in Florida or Maryland. The investigators evaluated the UCVA, BCVA, and Kmax values at 6 months and 1 and 2 years postoperatively.
A total of 381 eyes were evaluated. The average patient age was 33.5 years. The average corneal loading time was 36.5 minutes. The average preoperative Kmax value was 63.5 D. The average preoperative Pentacam pachymetry value was 407 µm (range, 181-449µm). Of the study eyes, 80% had keratoconus, 17% post-LASIK ectasia, and 3% pellucid marginal degeneration, Dr. Trattler reported.
The results indicated that there was progressive improvement in the Kmax values over time with subsequent improvements in the UCVA, BCVA, and astigmatism.
At the 6-month follow-up visit, 206 eyes were recorded of which the average improvement in the UCVA was 1.71 lines and the average improvement in BCVA was 0.68 lines, Dr. Trattler said. The average Kmax improvement from the baseline value was 0.75 D of flattening and the average decrease in the refractive astigmatism was 0.3 D.
By 1-year postoperatively, 153 eyes had completed their follow-up. The average improvement in the UCVA was 2.26 lines and the average improvement in the BCVA vision was 0.79 line. The average Kmax improvement from baseline value was 1.18 D of flattening, and the average decreased in the refractive astigmatism was 0.38 D.
Sixty-two eyes completed the 2-year follow-up, when the average improvement in the UCVA was 2.65 lines and in the average improvement in the BCVA vision was 1.18 lines. The average Kmax improvement from the baseline value was 1.23 D of flattening and the average decreased in the refractive astigmatism was 0.81 D.
A case study demonstrated the progressive improvement seen after the Epi-on CXL procedure. In this case of a 68-year-old man, his preoperative Kmax value was 50.6 D, 18 months after surgery the KMax was 45.9 D, and at 3 years the Kmax was 44.9 D.
CXL is effective for stopping progression of keratoconus, post-LASIK ectasia, and pellucid marginal degeneration, Dr. Trattler reported. In addition, CXL can help improve the corneal shape, UCVA, BCVA and quality of vision.
If progression occurs after either the Epi-off or Epi-on CXL procedures, the treatment can be repeated safely, he said.
“Our clinical study showed that the Epi-on CXL procedure with pulsed UV light for treating patients with thin corneas appears to be as effective as the Epi-off procedure,” Dr. Trattler concluded.
William Trattler, MD
Dr. Trattler has a financial interest in this technology. He was joined in this data analysis by Roy Rubinfeld, MD, MA, who has a financial interest in this technology.