contact lens care and compliance
Choose Rewetting Drops and Artificial Tears With Care
BY MICHAEL A. WARD, MMSC, FAAO
Dry eye symptoms are a major contributor to contact lens dropout. Dryness symptoms may result from dry eye, or they may result from a tight-fitting lens or from lens care product sensitivity. Lubricating/rewetting drops may help relieve symptoms — or may make them more profound depending on the dosage and types of drops chosen.
Rewetting Drop Components
Most rewetting drops are preserved, multi-dose products that may contain electrolytes, buffers, and wetting agents (Table 1).
Common wetting agents/ lubricant components include carboxy methylcellose (CMC), hydroxypropyl methylcellulose (HPMC), and hyaluronic acid (HA). Surfactants (surface active agents) are amphiphilic: they contain both hydrophobic ‘tails’ and hydrophilic ‘heads,’ which reduce the interfacial tension between oil and water. This property results in the slipperiness of detergents. Too much surfactant can emulsify the lipid tear layer, exacerbating dryness.
Preservatives are another double-edged sword. All preservatives have the potential to be toxic. Their goal is to maintain product sterility, while avoiding damage to ocular tissues. Overuse of preserved drops may create a toxic preservative load that can mimic dry eye. As a rule of thumb, preservative load should be limited to four doses each day. Dissipating preservatives such as perborate and stabilized oxychloro complex are less likely to cause preservative cytotoxicity.
Avoid Preserved Artificial Tears
Do not confuse artificial tears with contact lens rewetting drops. Preserved artificial tears may contain preservatives such as benzalkonium chloride (BAK) that are contra-indicated for soft lens use. BAK interferes with cellular mitosis, slows epithelial healing, and can cause a toxic keratitis when used in conjunction with soft contact lenses.
However, patients may safely use most preservative-free artificial tears over their soft contact lenses. CLS
Mr. Ward is an instructor in ophthalmology at Emory University School of Medicine and Director, Emory Contact Lens Service.