When i open this refresh tears eye drops how many days should i use it or how many days after opening it will be expire?

As needed: Refresh tears may be used as follows: 1-2 drops every 1 to 4 hours as needed for ocular dryness. Sometimes you may have to use the product frequently for excessive dryness, whereas other times less frequently. You may also try refresh optive, liquigel for drier eyes. The bottle itself has the expiration date printed on it. Discard the bottle if expired, contaminated, or empty.