High Oxygen Epi-On Protocol Shows Promise for CXL Treatments

Anovel high-oxygen epithelium-on (epi-on) treatment protocol may be a promising alternative to epi-off protocol in room air for customised cross-linking in keratoconus patients, according to preliminary data from an ongoing study by Anders Behndig MD, PhD and colleagues.

“So far, our results indicate the novel high-oxygen epi-on treatment protocol may offer certain advantages compared to epi-off customised cross-linking. We hope to be able to confirm the data when the final results are available in the near future,” Dr Behndig said.

Dr Behndig’s study compared the efficacy, safety, and healing phases of two different customised remodelled vision (CuRV) cross-linking protocols in 45 patients treated bilaterally for keratoconus: one eye with epi-on CuRV with high oxygen and one eye with epi-off CuRV in room air.

The treatment protocol used HPMC-based riboflavin application for 10 minutes followed by individualised treatment patterns with a maximum effect of 7.2 to 15 joules/cm2, with energy distribution determined by the maximum keratometry reading (Kmax). The posterior corneal surface was the basis for treatment localisation, with the maximum effect at the steepest point of the corneal posterior surface and a tapering of 2 joules per 2 D of reduced effect towards the periphery. There was a 6 mm vertex centred zone for all eyes treated with 5.4 joules/cm2 .

For the epi-on eye, humidified oxygen at 2.5 litres per minute was flushed over the eye during the whole treatment. The treatment time was always 16 minutes and 40 seconds, which Dr Behndig explained is important because the chemical reaction in cross-linking is oxygen dependent.

Dr Behndig first noticed this difference when previously performing treatments on low-grade myopia. When he treated patients in normal room air, there was almost no effect, but when Dr Behndig enhanced the oxygen concentration around the cornea by applying goggles and flushing oxygen into it, he obtained a much higher cross-linking effect.

This explains why accelerated cross-linking protocols will have less effect, noted Dr Behndig, as the oxygen is consumed too quickly. “High energy and short time are not the same as low energy and a longer time,” he said.

In terms of results, Dr Behndig said there was significantly less pain from eight hours after treatment in the epi-on eyes. Corrected and uncorrected distance visual acuity improved at key follow-up intervals out to 12 months for both groups, with no differences between the treated eyes.

However, low contrast visual acuity improved faster with the epi-on protocol, with improvement at one month for epi-on and at six months for epi-off eyes. There were no significant differences between the groups at six and 12 months. The safety data showed an improvement in corrected distance visual acuity, with no adverse events and no change in endothelial cell counts, he concluded.

Dr Behndig presented these results at the ESCRS Virtual Winter Meeting 2022.

Anders Behndig MD, PhD is Professor of Ophthalmology at Umeå University Hospital, Umeå, Sweden. anders.behndig@umu.se

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