Phototherapeutic keratectomy-assisted, customized, epi-on corneal crosslinking: A different approach for treating keratoconus
(Image credit: AdobeStock/bdavid32)
Farhad Hafezi, FARVO, MD, PhD, and colleagues reported on the results achieved with phototherapeutic keratectomy (PTK)-assisted, customized, epi-on corneal crosslinking (CXL) (PACE), from the Swiss-based Elza Institute) that is a new take on CXL, in that it is not intended to just stable corneal tissue but to provide profoundly improved vision in patients with keratoconus (KCN) without ablating tissue. Hafezi, Professor of Ophthalmology, University of Geneva, Switzerland, described his team’s 1-year results with the procedure at the 2024 American Academy of Ophthalmology Annual Meeting in Chicago.
“This procedure is different from the CXL we have been using for the past 20 years. ELZA-PACE is unlike all previous combinations of the excimer laser and CXL for vision rehabilitation such as, for example, the Athens and Cretan protocols, selective transepithelial topography-guided photorefractive keratectomy combined with accelerated corneal crosslinking, and topo-guided removal of epithelium in keratoconus, in that no stromal tissue is removed.
Briefly, the PACE procedure involves an epithelial map-driven PTK performed over the cone with no removal of stromal tissue. The customization is achieved by closely combining technologies: the entire cornea receives an epi-on treatment, in the presence of an epi-off window over the tip of the cone. Riboflavin then is instilled into the cornea, with the highest concentrations in the epithelium-denuded (cone) region and a concentration gradient toward the periphery. The third step consists of a selective second irradiation immediately after the first in which the periphery is covered and the center is treated.
PACE effects
To date, almost 300 patients have undergone PACE. Of these, about 150 have reached the 1-year follow-up time point.
In a representative case, Hafezi reported a patient who went from 0.4 to 1.0 corrected distance visual acuity with glasses. He demonstrated the topographic results that showed rapid and extensive flattening and a gain of 6 lines of vision 1 week after treatment.
This effect differs from excimer laser treatments using, for example, wavefront-guided PRK, in that stromal tissue is not removed as in PRK. The change in vision in PACE is the result of a massive remodeling and coupling cross-linking effect, not an ablative effect.
The key is that the CXL effect is focused at the tip of the KCN. The corneal measurements generally reveal an oval-shaped cone. “We create a custom offset, custom-size PTK that very tightly hugs the tip of the cone and it is epithelial map driven. The treatment does not extend into the stroma, but stays within Bowman's layer. By so doing, this results in an epi-off window, an area that reacts with greater flattening than the epi-on area because nothing impedes the ultraviolet light,” Hafezi explained.
The take-home message is that this procedure differs from an excimer laser treatment where the excimer laser provides the effect. This is a treatment in which the entire effect comes from cross-linking.
Hafezi explained that when all cases have reached the 1-year follow-up point, the data will be analyzed and possibly allow prediction of the degree of flattening in a given eye.
Reference:
Hafezi F, Torres Netto EA, Awwad ST, et al. One-year clinical experience with PACE (second-generation customized CXL) to reduce corneal topographical asymmetry and improve vision in patients with KCN. Presented at the 2024 American Academy of Ophthalmology Annual Meeting, Chicago; October 19-21. Presentation: Cornea, External Disease; session: PA034
