Inclusion Criteria:  patients with open angle galucoma or ocular hypertension that had been controlled (stable IOP <19mmHg) by commercially available preserved PGA -timolol FC for at least 3 months Stable visual field (based on at least two reliable visual field tests performed within the last 12 months) Central corneal thickness within the range 500-580µm. mild to moderate hyperaemia based on MacMonnies (scores 1 and 2)  Exclusion Criteria:  Best-corrected visual acuity (BCVA) 0,1 or lower Severe visual field defects (MD 12 dB or higher) Any intraocular surgery (other than filtration surgery performed at least 6 months before screening) Any ocular surface abnormality preventing accurate IOP measurement Acute ocular inflammation Contact lens wearers