Usually preservatives are added into the eye drop solution to destroy the microorganisms which may be introduced during manufacture or use. There a many types like benzalkonium, chlorhexidine, thimerosal, chlorbutanol, polyquad.
Benzalkonium chloride (BAK) is often used because of its stability, excellent antimicrobial activity and long shelf life. But Benzalkonium chloride actually have toxic effects on both the tear film and corneal epithelium. A single drop of 0.01% BAK can break the superficial lipid layer of the tear film into numorous oil droplets. This preservative can reduce the tear film breakup time and thus may represent a poor choice for an antimicrobial preservative in artificial tear products.BAK can be retained in ocular tissues for up to 7 days and thus repetitive use may lead to cumulative effect. Long term use can damage conjunctival and corneal epithelial cells.
It makes the matter worse if the person is wearing a contact lens as the contact lens can act as a reservoir for BAK.
So what is the conclusion?
If it is really harmful, i think the health ministry must have taken action long time ago. There are so many considering factors involved, especially the cost.
Almost all bottled eye drops use BAK as its preservative. Even the antimicrobial eye drop itself like Chloramphenicol and Ciprofloxacin eye drop also contains BAK. Do we really have a choice here?
Ask the pharmacist!
1)Ask yourself whether u are going to use the artificial tears long term? If price is not a problem, always choose the best option available, which is preservative free artificial tears vial.
Some of the preservative free artificial tears2) Contact lens user, maybe it is better to use spectacles? i have been using specs for the past 16 years++.
3) As usual, consult your ophthalmologist or doctor or pharmacist for advise.
4) For further reading, pls visit here.