My mother saw a new opth.She has been taking these drops for 20 years with 2 previous opth.treating her.She asked and was previously told that it did not matter when she took her daily dose. Recently her pressure was up and she was referred to a new Dr who told her it is not effective if at taken at night. Something about not manufacturing that particular fluid during sleep which is more liquified during the day and the medicine is nore easily absorbed.