a randomized, investigator-blind, interventinal study will compare the effect of benzalkonium-chloride (BAK) preserved and preservative-free (PF) eye drops on conjunctival goblet cells.

The investigators will conduct a randomized, investigator-blind, interventinal study on 28 subjects. Each subject will apply a benzalkonium-chloride (BAK) preserved eye drop (Xalatan) in one eye and a preservative-free (PF) eye drop (Monoprost) in the other for 3 months. Which eye gets which treatment is randomized. Before and after treatment a conjunctival print will be made and the effect of the eye drops on goblet cell density will be evaluated along with effect on the intraocular pressure.

Inclusion Criteria:

1. Age >18years
2. Danish speaking
3. Open angle glaucoma or ocular hypertension
4. Average intraocular pressure equal to or above 22 mmHg

Exclusion Criteria:

a. history of significant eye diseae (including okular trauma) other than open angle glaucoma and ocular hypertension d. treatment with steroids within the last 3 months from inclusion e. Significant untreated systemic disease such as hypertension, heart failure, diabetes mellitus, stroke, lung disease and autoimmune diseases. Diseases are not reason for exclusion if they are well treated or does not need treatment g. pregnant or breast feeding h. women using unsafe anticonception i. allergy towards trial medication j. patients who cannot cooperate in eye examination k. ocular surface defects l. need for polytherapy in glaucoma treatment