contact lens care
Lubricating Drops May Improve or Worsen Lens-Related Dry Eye
BY MICHAEL WARD, MMSC, FAAO
Dry eye symptoms are a major contributor to contact lens drop out. Their presence doesn't necessarily mean that a patient has dry eyes -- symptoms may result from a tight lens fit or lens care product sensitivity. Lubricating drops may help to relieve symptoms or make them more profound depending on the dosage and types of drops chosen.
Table 1 lists popular commercially available rewetting drops, their lubricants and preservatives. Ophthalmic demulcents (soothing, usually mucilaginous or oily substances used to relieve pain in inflamed or irritated mucus membranes) are the active ingredients in lubricating drops. Surfactants also increase a product's lubricity because their bipolar nature creates a slippery surface.
Most rewetting drops are preserved, multi-dose products that contain sodium and potassium salts along with buffers. They may also contain other electrolytes, surfactants and emulsifiers. Patients may use preserved lubricating drops during lens wear at any time during the day, but shouldn't exceed four doses each day. Overuse of preserved drops may create a toxic preservative load that can mimic dry eye.
In-Eye Protein Removers
Complete Blink-N-Clean (Advanced Medical Optics) and Clerz Plus (Alcon) both reduce protein buildup, rewet and clean lenses during wear. Blink-N-Clean is a PHMB-preserved solution that uses tromethamine as the emulsifier/buffer, HPMC as the lubricant, tyloxapol as a surfactant and EDTA as a chelant.
Clerz Plus is a Polyquad-preserved solution that uses Tetronic 1304 as its surfactant/wetting agent and RLM-100 (lauryl ether carboxylic acid) as its surfactant. The dose for lens lubrication differs from the dose for preventing protein deposition.
Patients may safely use most nonpreserved artificial tears over soft contact lenses. However, some preserved artificial tears use 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 over soft lenses. Nonpreserved drops don't have a theoretical dosing limit, which is to say that no concern for preservative build up exists.
Mr. Ward is an instructor in ophthalmology at Emory University School of Medicine.