The overall objective of this study is to optimise the corneal cross-linking standard protocol in terms of a more economical use of the resource "medical personnel" and in terms of increased patient participation. If it can be shown that the riboflavin necessary for corneal cross-linking does not necessarily have to be applied directly on the cornea (as currently performed by the nurses), but can also be applied in the inferior fornix (as it would be performed by patients in the context of self-application), then it would be conceivable to transfer this task from medical staff to the patients.

This national single-centre, experimental, randomized and controlled trial will comprise two parallel arms. The intervention to be studied will be an alternative application of riboflavin drops in the inferior fornix. As comparator serves a conventional riboflavin drop application directly on the center of the cornea. Our research hypothesis is that the application of riboflavin drops in the inferior fornix is not inferior to the corneal application with respect to the resulting riboflavin concentrations in the anterior chamber; which represents a sufficient corneal impregnation with riboflavin. This study is randomized but not blinded. Recruitment is anticipated to start in September 2019 and is scheduled to last 1-2 months. We will enroll 12 patients in each trial arm.

Inclusion Criteria:

• Healthy clinical staff members of the Dept. of Ophthalmology at the Lucerne Cantonal Hospital will be evaluated for study inclusion.
• Signed written informed consent form

Exclusion Criteria:

• Aged < 18 years
• Any ocular or systemic diseases with ocular side effects
• Medication with potential ocular side effects
• Epilepsia, due to the flickering light of the fluorophotometer used to measure anterior chamber riboflavin concentration