Assessing Transepithelial Surface Ablation Benefits
Epi-on and epi-off appear to produce similar outcomes.
Published: Tuesday, August 29, 2023
Transepithelial surface ablation offers a safe, effective, and predictable method of refractive correction in topography-guided photorefractive keratectomy (PRK) and phototherapeutic keratectomy (PTK) procedures, according to Dr Jesper Hjortdal.
In traditional PRK procedures, the corneal epithelium is mechanically removed, most often alcohol assisted, to enable the excimer laser to reshape the cornea. Although successfully deployed for more than 30 years, PRK recovery time is typically longer than LASIK, primarily due to the healing of the corneal epithelium. This prompted the evolution of PRK without epithelial removal to provide theoretically faster healing, faster visual recovery, and better predictability, Dr Hjortdal said.
He noted transepithelial ablation presents its own unique challenges for the surgeon.
“The corneal epithelium is thicker towards the periphery, where the excimer laser is less efficient. The ablation rate of the epithelium is different than the stroma,” he said. “To ensure a controlled stromal ablation, we can increase the number of excimer laser spots in the periphery, use online measurements of the epithelial thickness profile, or use a platform with laser nomograms specifically designed to perform transepithelial PRK.”
He did point out very few randomised controlled trials in the scientific literature compare the two approaches.
A recent meta-analysis by Alasbali included 12 experimental and interventional studies from 2011 to 2021 comparing PRK with and without epithelium, but only two of those studies were randomised controlled trials.1
In terms of visual outcomes, Alasbali found no difference between PRK with epithelium (TPRK) and without epithelium (PRK) for uncorrected distance visual acuity (UDVA) and spherical equivalent refraction. Corneal haze results were also similar in both procedures. However, there was a faster healing time for TPRK than PRK.
“My interpretation of the study conclusion based on the forest plots indicate the traditional outcome measures are comparable after PRK with and without epithelium, but epithelial healing may be faster after PRK with epithelium,” Dr Hjortdal said.
A contralateral randomised controlled study revealed the visual and refractive outcomes were similar with or without epithelium.2 Furthermore, although the time to complete re-epithelialisation was similar, the epithelial healing rate was faster in conventional PRK, considering the initial corneal epithelial defect area. Patients also experienced less pain and discomfort in the first postoperative day.
Deploying transepithelial ablation can also reduce visual symptoms after complicated SMILE procedures—though Dr Hjortdal added it was important to use mitomycin C after the ablation to reduce the risk of haze development.
The transepithelial approach provided a viable treatment option for a young patient diagnosed with homozygous granular corneal dystrophy type II at six years old.
“She has had repeated transepithelial ablations over many years,” Dr Hjortdal explained. “We always use mitomycin C. She is 17 years of age now, and her visual acuity is 0.4.”
Dr Hjortdal presented at the 2023 ESCRS Winter Meeting in Vilamoura, Portugal.
For citation notes, see page 54.
Jesper Hjortdal MD, PhD is Clinical Professor at Aarhus University Hospital, Denmark. email@example.com