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Results of a prospective study using individualized fluence corneal-cross-linking in ultra-thin corneas – the sub400 protocol

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First Author: F.Hafezi SWITZERLAND

Co Author(s):    E. Torres-Netto   F. Gilardoni   S. Kling   R. Abrishamchi   H. Abdshahzadeh   N. Hafezi     

Abstract Details

Purpose:

Current treatment options for corneal cross-linking (CXL) in corneas thinner than 400 µm include swelling of the stroma with hypo-osmolaric riboflavin or application of a contact lens. Both methods aim at artificially increasing stromal thickness and go along with highly variable outcomes and reduced efficacy. In 2017, we published a new algorithm: rather than modifying corneal thickness, we adapt the total irradiation (fluence) to every patient’s individual stromal thickness (sub400 protocol). In this prospective clinical study, we analyzed whether CXL with individualized fluence is able to stop keratoconus progression in ultra-thin corneas with a follow-up of 1 year.

Setting:

The study was conducted jointly at the Laboratory for Ocular Cell Biology, Center for Applied Biotechnology and Molecular Medicine at the University of Zurich (Switzerland) and the ELZA Institute AG, Dietikon (Switzerland).

Methods:

A total of 47 progressive keratoconus (KC) eyes with corneal thicknesses between 214 μm and 398 μm at the time of UV irradiation were enrolled. Following a standardized riboflavin application for 20 minutes, UV irradiation was performed at 3 mW/cm2 with individualized irradiation times. CDVA, manifest refractive sphere, cylinder, Kmax, thinnest corneal thickness and densitometry were evaluated preoperatively, and at 6 and 12 months postoperatively. Corneal demarcation line was assessed with anterior segment OCT at 1 month after surgery. Keratoconus progression was defined as increase of Kmax by >1.0 D within 1 year.

Results:

5 of 47 eyes showed progression within 12 months. A significant correlation was found between demarcation line depth and irradiation time (r=+0.423, p=0.003), however not between demarcation line depth and change in Kmax (r=-0.129, p=0.387). On average, there was a significant change from baseline at 12 months in thinnest thickness (-16.8±23.9 μm, p<0.05), in Kmax (-2.15±3.60 D, p<0.05) and in densitometry (+2.00±2.07 GSU, p<0.05). No significant changes were found in CDVA (p=0.471), sphere (p=0.206) and cylinder (p=0.753).

Conclusions:

The “sub400” individualized fluence CXL protocol standardizes the treatment in ultra-thin corneas and halted KC progression with a success rate of 89% at 12 months. The sub400 protocol allows for the treatment of corneas as thin as 215 µm of corneal stroma, extending the clinical range of cases that can be safely cross-linked to far progressed keratoconus stages. Demarcation line depth did not predict treatment outcome and hence is likely not related to the extent of CXL-induced corneal stiffening, but rather to the extent of induced wound healing.

Financial Disclosure:

... has significant investment interest in a competing company, ... receives non-monetary benefits from a company producing, developing or supplying the product or procedure presented