Answer
A harmless white residue can appear when the viscous drops dry. It can be gently wiped away with clean cotton wool.
Sources for this answer
- Fusidic Acid 1% Viscous Eye Drops / Fucithalmic 1% w/w Viscous Eye Drops — Current selected SmPCemc · Summary of Product Characteristics
General medicine information. Follow the instructions for your own medicine and speak to a pharmacist or clinician about your individual circumstances.