Glaucoma is one of the leading causes of blindness in the west. The disease caused by high intra ocular pressure (IOP) and characterized by damage to the optic nerve and gradual loss of visual field. Intra ocular pressure change during the day. To evaluate the efficiency of the therapy it is common to measure the intra ocular pressure at different times of the day. Most ophthalmologists admit the patient for one day at which intra ocular pressure is measured at different times. This method does not mimic the patient daily routine and may not reflect the true diurnal fluctuations.