[Preservatives in eye drops: toward awareness of their toxicity]

Preservatives are present in numerous multidose eyedrops and provide the sterility of the solution against bacteria and fungi. However, numerous studies have shown their toxicity for the ocular surface, particularly in long-term treatments. The most widely used preservative in eyedrops is benzalkonium chloride. This quaternary ammonium acts as a detergent, antiseptic, disinfectant, fungicide, bactericide, and spermicide. Its use on the ocular surface therefore has significant consequences. Indeed, the preservatives are pro-apoptotic, pro-inflammatory and they cause the dissolution of the lachrymal film. The prolonged administration of one or several eye drops containing preservatives induces changes in the superficial structures (conjunctiva, cornea) as well as in deeper structures (trabecula, lens). The least severe symptoms are irritation and discomfort, including sensation of a foreign body, itching, or burning sensations. However, more severe side effects have been described, such as chronic inflammation of variable intensity or the progressive development of fibrosis with higher risk of failure after glaucoma filtering surgery. Ideally, preservative-free eyedrops should be recommended, or at least a reduction of the number of instilled preserved eyedrops should be considered. All these strategies could increase patient comfort, quality of life, and compliance, with better outcome at the time of filtering surgery.