Second-Generation “Sub400” Protocol For Corneal Cross-Linking In Ultrathin Corneas: One-Year Follow-Up Data

Published 2024 - 42nd Congress of the ESCRS

Reference: PO666 | Type: Free paper | DOI: 10.82333/w4ka-t790

Authors: Emilio A. Torres-Netto* ¹ , M. Enes Aydemir ² , Mark Hillen ² , Léonard Kollros ² , Nikki Hafezi ² , Boris Knyazer ³ , Ludmilla Nascimento ⁴ , Luciene Barbosa ⁴ , Frank Blaser ⁵ , Farhad Hafezi ²

¹ELZA Institute,Zurich,Switzerland;University of Zurich,Zurich,Switzerland;University of Geneva,Geneva,Switzerland, ²ELZA Institute,Zurich,Switzerland, ³Soroka University Medical Center, Faculty of Health Sciences, Ben-Gurion University of the Negev,Beer-Sheva,Israel, ⁴Federal University of São Paulo UNIFESP-EPM,Sao Paulo,Brazil, ⁵University Hospital Zurich,Zurich,Switzerland

Purpose

The original sub400 protocol is an epi-off CXL used to strengthen ultra-thin (~180–≤400µm) corneas. It uses pre-irradiation thinnest-point stromal pachymetry measurements and a validated algorithm to adapt irradiation duration (and therefore fluence), leaving a ~70 µm safety margin region above the endothelium. The original sub400 protocol is based on 3 mW/cm² intensity and a fluence of 5.4 J/cm2 at 400 µm of stromal thickness.

The second-generation sub400 protocol modifies this approach in two ways. First, its starting fluence increases from 5.4 to 10 J/cm2 at 400 µm of corneal stroma and second, it delivers the same efficacy and safety as earlier sub400 CXL but in a shorter (sub-20 minute) period. We will present one-year follow-up data.

Setting

The study was conducted at the ELZA Institute, Zurich, Switzerland.

Methods

The study included approximately 70 eyes with progressive keratoconus and corneal thickness below 400 µm, treated with the second-generation sub400 protocol. UV irradiation intensity was adjusted based on corneal thickness: 9 mW/cm² for cornea with pachymetries ≥330–400 µm, and 3 mW/cm² for those below 330 µm. Fluence at 400 µm of stromal thickness was 10 J/cm2 and was then consecutively lowered following our published algorithm. Outcome measures included keratoconus progression, visual acuity, and corneal topography and tomography, as well as corneal endothelial cell counts in a subset of patients.

Results

We will present one-year follow-up data of this cohort. Comprehensive data on the second-generation sub400 protocol's effectiveness in halting keratoconus progression and its impact on visual function and corneal morphology, and endothelial cell counts will be presented.

Conclusions

The second-generation sub400 protocol offers a tailored approach to CXL in ultrathin corneas, with UV irradiation intensity and duration adjusted according to specific corneal thickness measurements. Initial observations suggest no adverse effects on endothelial cell density, with forthcoming data expected to provide further insight into the protocol’s safety and efficacy in managing keratoconus over a one-year period.