To elucidate confounding factors in ocular surface microbiome research and to confirm the presence of a core ocular surface microbiome and its temporal stability.

The investigator will take a conjunctival sample of both eyes of a group of volunteers together with an extensive questionnaire. Furthermore, 50 volunteers will be sampled repeatedly during one year or two years.

Inclusion Criteria:

• The subject is fluent in written and verbal Dutch
• The subject is capable of giving informed consent

Exclusion Criteria:

• Use of glaucoma drops
• Use of antibiotic drops < 1 month before sampling