Can you tell me the standard recommendation for the shelf-life of over-the-counter eye drops once opened?

Can you tell me the standard recommendation for the shelf-life of over-the-counter eye drops once opened? My drops both have expiration dates of about 14 months from purchase, but it states nothing about once it is opened. Are they safe to continue using after several months?

Eye drops, once opened and used, risk being contaminated with the normal bacteria that live on your eyelids. Most bottles of eye drops contain preservatives which limit bacterial growth but not entirely. The older the bottle, the greater the chance that it has been contaminated, and the longer time the bacteria has to grow. A good rule of thumb is to throw away any opened bottle of eye drops after 3 months. Never share eye drops—eye infections can be spread this way. Never use someone else's prescription eye drops. Some people mistakenly think that all eye drops are alike, and they are not—some treat dry eye, some treat bacterial or viral infections, and some treat inflammation or glaucoma or fluid in the eye.