Xalatan © administration - the second eye will receive mono-treatment of Xalatan © (Pfizer, latanoprost mono-treatment eye drops) as an internal control. According to the manufacturer's instructions for use - the recommended dosage is one drop once daily. Study administration will be in the evening time. Reduction of the IOP starts approximately 3 to 4 hours after administration and the maximum effect is reached after 8 to 12 hours. Xalatan will be administered by the patient until end of the study, and mis-compliance will be documented in the CRF.