Is it ok to use over-the-counter artificial tears without being told by an eye doctor to use them?

Yes: Yes, artificial tears that do not have extra chemicals in them such as redness-relievers in them are always fine to use at any time. They can only help. If you use artificial tears in a bottle, there are preservatives in them and they should only be used 4-5x/day because the preservatives can irritate the eyes if used more. Preservative-free tears can be used indiscriminately with no problems.

Yes: These drops are over the counter because they are not regulated by the fda and are deemed not to be significantly harmful if taken without the supervision of a doctor. The only warning is that you take these drops understanding their limitations: they help lubricate an otherwise dry eye. If there is the chance that you have another eye condition, see an eye doctor before choosing these drops.

Yes: Yes. If you use more than an occasional drop i would recommend using a preservative free tear drop, so you don't develop an allergy to the preservative in the drop.

Yes: Yes, but if you do have persistent problems that you feel require artificial tears on a regular basis it would probably be good to get an eye exam.