These are rewetting drops that can be bought over the counter and used for dry eye. Artificial tears are produced by many manufacturers and are essentially all the same. The only real difference between them is what preservative is used to keep the drops sterile. This preservative is crucial for keeping the drops fresh and free of environmental bacteria. However, the preservative itself (especially BAK) can be irritating to the eye if the drops are used too often. Preservative-free artificial tears are available that eliminate this problem. They come in single-use disposable plastic dispensers and can be used as often as needed.