1. The United State Pharmacopoeia 24th revision. The National Formulary, 19th edition. Rockville, MD: The United States Pharmacopeial Convention, Inc.; 2000.
2. European Pharmacopoeia, 7th edition Strasbourg: Council of Europe; 2010.
3. Kallings LO, Ringertz O, Silverstolpe L. Microbiological contamination of medical preparations. Acta Pharm Suec. 1966;3(3):219-228.
4. Preservatives in eyedrops: The good, the bad and the ugly
5. Microbial contamination of multiply used preservative-free artificial tears packed in reclosable containers