Dry eye syndrome is a highly prevalent ocular disease with an increasing incidence in the elderly population. Topically administered lubricants are the basis for treatment of this disease. However, information about the corneal residence time of topical lubricants is still sparse, therefore no ideal treatment regimen has been found.

Recently a new method for assessment of tear film thickness based on optical coherence tomography (OCT) has become available. The aim of the present study is to assess corneal residence time of three different formulations of topical lubricants, in particular Thealoz Duo® Eye Drops, Hyabak® Eye Drops and Hydrabak® Eye Drops in patients with moderate dry eye disease. In addition, standard tests for dry eye syndrome, such as the ocular surface disease index (OSDI©), Schirmer I test and determination of tear break up time (BUT) will be performed..

Inclusion Criteria:

• Men and women aged over 18 years
• Signed and dated written informed consent.
• History of dry eye syndrome for at least 3 months
• Tear Break Up Time (BUT) ≤ 10 seconds or Schirmer I test ≤ 5 mm and ≥ 2mm
• OSDI (Ocular Surface Disease Index) ≤ 32 and ≥ 13
• Normal ophthalmic findings except dry eye syndrome, ametropia < 6 Dpt.
• No administration of topical lubricants 24 hours before the screening examination

Exclusion Criteria:

• Participation in a clinical trial in the 3 weeks preceding the study
• Symptoms of a clinically relevant illness in the 3 weeks before the first study day
• Presence or history of a severe medical condition as judged by the clinical investigator
• Intake of parasympathomimetic or anti-psychotic drugs
• Wearing of contact lenses
• Glaucoma
• Treatment with corticosteroids in the 4 weeks preceding the study
• Topical treatment with any ophthalmic drug except topical lubricants in the 4 weeks preceding the study
• Ocular infection or clinically significant inflammation
• Ocular surgery in the 3 months preceding the study
• Sjögren's syndrome
• Stevens-Johnson syndrome
• History of allergic conjunctivitis
• Ametropia >= 6 Dpt
• Pregnancy, planned pregnancy or lactating
• Known hypersensitivity to any component of the study medication.
• Any medical or surgical history, disorder or disease such as acute or chronic severe organic disease
• Inability to understand the study procedures