Epithelium-off corneal cross-linking surgery compared with standard care in 10- to 16-year-olds with progressive keratoconus: the KERALINK RCT
Authors: Larkin Daniel FP , Chowdhury Kashfia , Doré Caroline J , Bunce Catey , Burr Jennifer M , Caverly Emilia , French Lisa , Kopsini Dimitra , Klepacz Anne , Raynor Mathew , Edwards Matthew , Tuft Stephen J 
Published: October 2021

Background
Keratoconus is a disease of the cornea affecting vision that is usually first diagnosed in the first three decades. The abnormality of corneal shape and thickness tends to progress until the patient reaches approximately 30 years of age. Epithelium-off corneal cross-linking is a procedure that has been demonstrated to be effective in randomised trials in adults and observational studies in young patients.

Objectives
The KERALINK trial examined the efficacy and safety of epithelium-off corneal cross-linking, compared with standard care by spectacle or contact lens correction, for stabilisation of progressive keratoconus.

Design
In this observer-masked, randomised, controlled, parallel-group superiority trial, 60 participants aged 10–16 years with progressive keratoconus were randomised; 58 participants completed the study. Progression was defined as a 1.5 D increase in corneal power measured by maximum or mean power (K2) in the steepest corneal meridian in the study eye, measured by corneal tomography.

Setting
Referral clinics in four UK hospitals.

Interventions
Participants were randomised to corneal cross-linking plus standard care or standard care alone, with spectacle or contact lens correction as necessary for vision, and were monitored for 18 months.

Main outcome measures
The primary outcome was K2 in the study eye as a measure of the steepness of the cornea at 18 months post randomisation. Secondary outcomes included keratoconus progression, visual acuity, keratoconus apex corneal thickness and quality of life.

Results
Of 60 participants, 30 were randomised to the corneal cross-linking and standard-care groups. Of these, 30 patients in the corneal cross-linking group and 28 patients in the standard-care group were analysed. The mean (standard deviation) K2 in the study eye at 18 months post randomisation was 49.7 D (3.8 D) in the corneal cross-linking group and 53.4 D (5.8 D) in the standard-care group. The adjusted mean difference in K2 in the study eye was –3.0 D (95% confidence interval –4.93 D to –1.08 D; p = 0.002), favouring corneal cross-linking. Uncorrected and corrected differences in logMAR vision at 18 months were better in eyes receiving corneal cross-linking: –0.31 (95% confidence interval –0.50 to –0.11; p = 0.002) and –0.30 (95% confidence interval –0.48 to –0.11; p = 0.002). Keratoconus progression in the study eye occurred in two patients (7%) randomised to corneal cross-linking compared with 12 (43%) patients randomised to standard care. The unadjusted odds ratio suggests that, on average, patients in the corneal cross-linking group had 90% (odds ratio 0.1, 95% confidence interval 0.02 to 0.48; p = 0.004) lower odds of experiencing progression than those receiving standard care. Quality-of-life outcomes were similar in both groups. No adverse events were attributable to corneal cross-linking.

Limitations
Measurements of K2 in those eyes with the most significant progression were in some cases indicated as suspect by corneal topography device software.

Conclusions
Corneal cross-linking arrests progression of keratoconus in the great majority of young patients. These data support a consideration of a change in practice, such that corneal cross-linking could be considered as first-line treatment in progressive disease. If the arrest of keratoconus progression induced by corneal cross-linking is sustained in longer follow-up, there may be particular benefit in avoiding the later requirement for contact lens wear or corneal transplantation. However, keratoconus does not continue to progress in all patients receiving standard care. For future work, the most important questions to be answered are whether or not (1) the arrest of keratoconus progression induced by corneal cross-linking is maintained in the long term and (2) the proportion of those receiving standard care who show significant progression increases with time.

Trial registration
Current Controlled Trials ISRCTN17303768 and EudraCT 2016-001460-11.

Funding
This project was funded by the Efficacy and Mechanism Evaluation (EME) programme, a Medical Research Council (MRC) and National Institute for Health Research (NIHR) partnership. This will be published in full in Efficacy and Mechanism Evaluation; Vol. 8, No. 15. See the NIHR Journals Library website for further project information. The trial sponsor is University College London. This research was otherwise supported in part by the NIHR Moorfields Biomedical Research Centre and the NIHR Moorfields Clinical Research Facility, London, United Kingdom.