Artificial tears are lubricating eye drops specifically formulated to provide relief for dry eye symptoms like irritation and discomfort. These solutions supplement the natural tear film that protects the ocular surface. They add moisture and lubrication, thereby reducing friction and soothing the eyes. This temporary relief helps maintain eye comfort when natural tear production is insufficient or tear film stability is compromised.
The Foundation: Water and Primary Lubricants
Water forms the base of most artificial tear formulations, serving as the primary solvent for all other components. Lubricating and wetting agents are added to mimic the natural tear film’s aqueous and mucin layers. These ingredients provide hydration and create a smooth, protective surface over the eye.
Common lubricants include cellulose derivatives like carboxymethylcellulose (CMC) and hydroxypropyl methylcellulose (HPMC). These polymers increase the solution’s viscosity, allowing drops to remain on the eye longer and improving corneal wettability.
Hyaluronic acid, or its derivative sodium hyaluronate, also binds large quantities of water. This property helps lower tear osmolarity and stabilize the tear film, promoting even distribution. Glycerin and polyethylene glycol (PEG) are frequently included; glycerin acts as a humectant, attracting and holding moisture, while PEG forms a protective layer. Propylene glycol often accompanies PEG, further enhancing viscosity and moisture retention.
Tailoring Performance: Viscosity and pH Adjusters
Artificial tears incorporate agents to modify their physical properties, enhancing effectiveness and user comfort. Viscosity-enhancing agents, also known as thickening agents, prolong the eye drop’s residence time on the ocular surface. Common examples include carbomers, hydroxypropyl guar (HP-Guar), and dextran. These agents allow the solution to adhere better to the eye, providing sustained lubrication; some, like HP-Guar, even form a soft gel upon contact with the tear film.
Maintaining an optimal pH is important for comfort and formulation stability. Artificial tears typically include pH adjusters and buffering agents, such as sodium chloride, potassium chloride, borate buffers, or phosphates. These electrolytes help maintain the solution’s osmotic balance, mimicking the natural tear film’s pH of approximately 7.4. This balance contributes to comfortable application and helps prevent irritation, ensuring the eye drop remains stable throughout its shelf life.
A Key Consideration: Preservatives and Their Alternatives
Many multi-dose artificial tear bottles contain preservatives, chemical agents added to prevent bacterial contamination once opened. Common preservatives include benzalkonium chloride (BAK), polyquaternium-1 (Polyquad), and compounds like sodium perborate or Purite. While preservatives ensure product sterility and extend shelf life, some, particularly BAK, can cause irritation or toxicity with prolonged use. BAK, a detergent-type preservative, has been associated with corneal and conjunctival cell damage, interference with tear film stability, and loss of goblet cells.
Due to these potential downsides, preservative-free artificial tears are a common alternative, especially for frequent application. These formulations come in single-use vials discarded after one application, minimizing contamination risk. Some preservative-free multi-dose bottles are also available, utilizing specialized designs to prevent microbial growth. Polyquaternium-1 and “vanishing” preservatives like sodium perborate and Purite are considered less irritating than BAK because they are larger molecules or break down into harmless components upon contact with the eye.