Under normal circumstances, a bottle of eye drops in the case of sealed, according to the instructions on the use of 1-2 years, once the eye drops open after the start of use, the best time to use is no more than a month time. More than a month of eye drops, even from the appearance of transparency and cloudiness how much has not changed, it is best not to use. Because after opening the eye drops, with full contact with the air, the stability will become worse, even if the drops contain certain preservatives, but also prone to chemical changes, the composition of the drug effect will be more or less changed or reduced. The most important problem is that the bottle of eye drops does not pay attention to hygiene, contact with the eye is prone to contamination, plus repeatedly open the cap, the possibility of increased contamination is even greater. Patients are now advocated to use small packages of ophthalmic drugs without preservatives, and after the eye drops are opened, they are thrown away after more than 24 hours to avoid both contamination and damage to the eye surface from preservatives.