The prevalence and incidence of dry eye syndrome (DES) is constantly increasing. Several therapeutic strategies have been proposed, but still no ideal regimen has been found. Recently, a new method for the non- invasive measurement of tear film thickness (TFT) based on optical coherence tomography (OCT) has been developed. It has been shown in previous studies that TFT correlates well with objective signs as well as with subjective symptoms of DES.

In the present study the effects of three different topical lubricants (Neovis total multi®, Vismed multi® and Hydrabak® eye drops) on tear film thickness in patients with moderate to severe DES will be investigated using this device.

Tear film thickness will be measured at baseline and at defined time points after single instillation. The course of tear film thickness during this study day will provide information about the corneal residency time of the three different eye drops. Patients with moderate to severe DES will be randomized to receive either Neovis total multi®, Vismed multi® or Hydrabak® eye drops. Assessment of lipid layer thickness of the tear film will be performed before and at pre-specified time points after instillation as secondary outcome.

Other clinical measures for DES such as determination of tear film break up time (TFBUT), corneal fluorescein staining, Schirmer I test and subjective assessments will also be performed.

Inclusion Criteria

Patients will be eligible for inclusion if all these criteria are respected:

1. Age of at least 18 years
2. Provides written informed consent prior to study-related procedures at the screening visit
3. Is able to understand and willing to comply with the procedures and the actions asked of him/her
4. History of dry eye syndrome for at least 3 months
5. Reports at least 2 of the following symptoms related to dry eye syndrome: foreign body sensation, pain, itching, stinging, epiphora, photophobia or blurred vision
6. Tear Break Up Time (BUT) ≤ 10 seconds or Schirmer I test ≤ 10 mm
7. OSDI score ≥ 23 points
8. Normal ophthalmic findings except dry eye syndrome

Exclusion Criteria

Patients will be excluded under the following circumstances:

1. Participation in a clinical trial in the 3 weeks preceding the study
2. Symptoms of a clinically relevant illness in the 3 weeks before the first study day
3. Presence or history of a severe medical condition as judged by the clinical investigator
4. Intake of parasympathomimetic or anti-psychotic drugs
5. Wearing of contact lenses
6. Glaucoma in the medical history
7. Treatment with corticosteroids in the 4 weeks preceding the study
8. Topical treatment with any ophthalmic drug except topical lubricants in the 4 weeks preceding the study
9. Ocular infection or clinically significant inflammation not related to dry eye syndrome
10. Ocular surgery in the 3 months preceding the study
11. Sjögren's syndrome
12. Stevens-Johnson syndrome
13. History of allergic conjunctivitis
14. Pregnancy, planned pregnancy or lactating
15. Known hypersensitivity to any component of the study medication