The "dry eye syndrome" DES is a highly prevalent ocular disease, in particular in the elderly population. One mainstay of therapy for patients suffering from DES is the use of topically administered lubricants. However, despite many efforts, no "ideal" formulation has yet been found.

Recently, Croma Pharma has introduced chitosan-N-acetylcysteine eye drops, designed for treatment of symptoms related to DES. Chemically, chitosan is a polycationic biopolymer with favourable biological properties such as high biocompatibility and low toxicity. Additionally, the new formulation comprises N-acetylcysteine, which has been used in ophthalmology because of its mucolytic properties for several years. Based on theoretical considerations, one can hypothesize that the new chitosan derivative may show an increased adhesion to mucins of the ocular surface and may therefore be particularly beneficial in reducing the symptoms associated with DES. We have recently shown in a phase I trial that single instillation of chitosan-N-acetylcysteine eye drops is well tolerated in young healthy subjects. However, due to the fact that intraocular pressure has been measured as one of the main safety variables, topical anesthesia was necessary. Thus, the data about local ocular discomfort after administration are limited. This trial seeks to investigate whether single instillation of chitosan-N-acetylcystein leads to ocular discomfort such as burning and stinging.

Inclusion Criteria:

• Men and women aged between 18 and 45 years
• Normal laboratory values unless the investigator considers an abnormality to be clinically irrelevant
• Normal findings in the medical history and physical examination unless the investigator considers an abnormality to be clinically irrelevant
• Normal ophthalmic findings, ametropia < 6 dpt

Exclusion Criteria:

• Participation in a clinical trial in the 3 weeks preceding the study
• Abuse of alcoholic beverages
• Symptoms of a clinically relevant illness in the 3 weeks before the first study day
• Ametropia less than 6 dpt
• Pregnancy