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, no data is yet available about safety and tolerability of chitosan-N-acetylcysteine in subjects wearing contact lenses. This is of special interest because the tear film is critical to successful contact lens wear. Disturbances of the quantity or quality of the tear film results in intolerance of contact lens wear and possible damage to the ocular surface. This trial seeks to investigate the local tolerability and possible ocular discomfort of chitosan-N-acetylcysteine eye drops after repeated instillation .

Inclusion Criteria:

• Regular contact lens wear since 3 years minimum
• Daily wearing time of the contact lens of 8 hours or more
• Good tolerability of the contact lenses without ocular discomfort or local signs of chemosis, conjunctival redness or other signs of intolerability as judged by the investigator.
• Subject willing to continue contact lens use for the study period
• 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 except ametropia

Exclusion Criteria:

• Participation in a clinical trial in the 3 weeks preceding the study
• Use of colored contact lenses
• Abuse of alcoholic beverages or other drugs
• Symptoms of a clinically relevant illness in the 3 weeks before the first study day
• Pregnancy