Over-the-counter eye drops, commonly known as artificial tears, are topical solutions designed to supplement the eye’s natural moisture barrier and provide lubrication. They are the first line of defense for addressing discomfort, dryness, and irritation caused by environmental factors or various ocular conditions. Their primary function is to increase the volume of the tear film and stabilize its layers to protect the delicate surface of the eye. This article focuses specifically on non-preserved formulations, which offer an alternative for individuals with sensitive eyes or those who require frequent daily use. These preservative-free products use advanced delivery systems to ensure sterility without chemical additives.
Why Preservatives Are Excluded
Preservatives are included in multi-dose eye drops to prevent microbial contamination once the bottle is opened. However, the most common preservative, benzalkonium chloride (BAK), is a detergent that can have negative effects on the ocular surface, especially with chronic or frequent application. BAK causes dose-dependent toxicity by disrupting the lipid layer of the tear film, leading to instability and increased evaporation. This can worsen dry eye symptoms, causing burning, discomfort, and a foreign body sensation.
On a cellular level, BAK is cytotoxic, meaning it can damage cells on the surface of the eye. Chronic exposure causes inflammation, loss of mucin-producing goblet cells, and epithelial cell apoptosis (cell death) in the cornea and conjunctiva. This long-term damage is why specialists recommend preservative-free options for patients using drops more than four times a day or those with moderate-to-severe dry eye disease. Removing the preservative makes the drop formulation significantly gentler on sensitive ocular tissue.
Types of Non-Preserved Formulations
Manufacturers utilize sophisticated packaging technology to maintain sterility in the absence of chemical preservatives. The most recognizable format is the single-use or unit-dose vial, which is sealed and sterile until opened. Since the vial is meant to be used once and discarded, there is no risk of bacterial contamination from repeated use. These vials are highly recommended for sensitive eyes and post-surgical care, though they can be less convenient and more costly.
A major advancement is the development of specialized multi-dose bottles that allow for repeated use without preservatives. These systems employ purely mechanical means to prevent external contaminants from entering the solution.
Multi-Dose Systems
One common design uses a non-return valve combined with a fine filtering membrane, such as the ABAK® system, which allows the liquid out while filtering air and contaminants that try to enter. Other technologies, like the Ophthalmic Squeeze Dispenser (OSD) or Novelia® bottle, use a combination of a one-way valve and a tip-seal or silicone membrane. These mechanisms prevent backflow and filter the air that enters to compensate for the dispensed drop volume. This design allows for a larger, more convenient bottle while still delivering a sterile drop.
Key Lubricating Ingredients and Their Function
The effectiveness of non-preserved drops stems from their lubricating and protective ingredients, which serve different purposes depending on the underlying cause of dry eye. Hyaluronic acid (HA), often listed as sodium hyaluronate, is a highly effective demulcent known for its ability to bind large quantities of water. HA functions as a viscosity-enhancing agent, increasing the drop’s retention time on the eye and promoting epithelial cell proliferation and wound repair.
Other common polymers, such as Carboxymethylcellulose (CMC) and Polyethylene Glycol (PEG), also increase the viscosity of the tear film, improving its stability and thickness. CMC is a plant-derived cellulose that provides mucoadhesive properties, allowing the drop to stick to the ocular surface longer. PEG, often combined with other glycols and polymers, creates a protective mesh that binds to damaged cells, helping to restructure the tear film and provide lasting protection.
For individuals with evaporative dry eye, caused by a deficiency in the tear film’s outer lipid layer, lipid-based drops are necessary. These formulations utilize ingredients like mineral oil, castor oil, or specialized seed oils such as Sacha Inchi oil. These oils are formulated as microemulsions to supplement and stabilize the natural lipid layer, which significantly reduces the rate at which the aqueous component evaporates. Combining these lipid components with aqueous enhancers like glycerin or HA creates a drop that targets both aqueous and evaporative components, providing comprehensive relief for mixed-type dry eye.
Safe Usage and Storage Guidelines
Proper handling and storage are important for all non-preserved eye drops to maintain their sterility. For single-use vials, the guideline is to discard the container immediately after administering the drops, even if liquid remains. Reusing a single-use vial, even a few hours later, risks introducing bacteria into the eye since the contents lack a preservative to inhibit growth.
Specialized multi-dose bottles, while more convenient, also have strict in-use expiration dates once opened. Depending on the mechanical system used, these drops must be discarded between 28 days and six months after the first use, with the specific time frame listed in the product instructions. To prevent contamination, users must avoid touching the dispenser tip to the eye, eyelid, or any other surface during application. All eye drops should be stored at room temperature, away from extreme heat or cold, and never used past the expiration date printed on the packaging.