Epithelial thickness mapping used to guide phototherapeutic keratectomy
Transepithelial phototherapeutic keratectomy with epithelial thickness mapping reduced stromal irregularities and improved vision in cases of irregular astigmatism, according to a study.
The study authors retrospectively analyzed 30 eyes that underwent transepithelial phototherapeutic keratectomy (TE-PTK) only and 11 eyes that underwent TE-PTK with subsequent refractive surgery, with the goal of defining a standard treatment protocol based on population epithelial thickness measurements.
A Mel 80 excimer laser (Carl Zeiss Meditec) was used to perform all TE-PTK procedures. An Artemis very high-frequency digital ultrasound scan (ArcScan) was used to generate preoperative epithelial thickness maps. Visual and refractive outcomes were analyzed 12 months after treatment, and change in epithelial thickness range was used to evaluate the effectiveness of stromal surface regularization.
Postoperatively, corrected distance visual acuity improved by one or more lines in 58% of eyes. One eye lost one line, and no eyes lost two lines.
Significant stromal surface regularization was achieved when average epithelial thickness range was reduced from 41 µm to 29 µm, according to the authors.
Fifty-nine percent of eyes in the TE-PTK group had an unpredictable refractive shift with a change of more than 0.50 D. Refractive accuracy in the TE-PTK with refractive ablation group was acceptable; however, there were two outliers outside the standard deviation of 1 D.
The authors identified a therapeutic window with epithelial thickness between 51 µm and 60 µm.
“A standard protocol of targeting an initial TE-PTK ablation for 55 µm will likely achieve breakthrough of the thinnest epithelium without total epithelial removal, allowing the treatment to be continued in a stepwise fashion,” the authors wrote.
Disclosure: Reinstein is a consultant for Carl Zeiss Meditec, has a proprietary interest in Artemis technology (ArcScan) and is an author of patents related to very high-frequency digital ultrasound administered by the Cornell Center for Technology Enterprise and Commercialization in Ithaca, NY.