Polyvinyl alcohol eye drops belong to a kind of artificial tears, this kind of eye drops does not contain preservatives, so the packaging of the drug is usually a single package, each eye drops use time limit within 24 hours. The correct usage should be to open an eye drop every morning and then dot the eyes 3-4 times, which can be evenly separated, such as 4 times in the morning, noon, afternoon and evening, and then discard the eye drops when you are done with them at night. Within 24 hours, the eye drops have not deteriorated and can be used, but if you forget to use them after the night, or if there is still residual eye drops, you can no longer continue to use them until the morning of the second day, in which case you should promptly discard the eye drops to avoid side effects from drug deterioration.