Products
Tear substitutes are available as eye drops or eye gels in the form of single doses (monodoses, SDU, UD) and in vials. The monodoses do not contain preservatives and are usually suitable for contact lens wearers. The vials may contain a preservative and have a limited shelf life after opening. However, there are those available that can be used for up to 6 or even 12 months after opening. Some tear substitutes are approved as drugs, while others are approved as medical devices. Products include, for example, Bepanthen eye drops, Cellufluid, Hylo-Comod, Lacrycon, Protagent, Systane, and Viscotears (selection).
Structure and properties
Tear substitutes usually contain water-binding (hygroscopic) and gel-forming polymers, such as hyaluronic acid, cellulose derivatives, carbomers, polyethylene glycols, or povidones. The agents may contain additives and active ingredients such as salts, lipids, vitamins such as dexpanthenol and vitamin A, plant extracts such as eyebright, and ectoine.
Effects
Tear substitutes (ATC S01XA20) moisturize the eye and counteract irritation and the sensation of foreign bodies. They form a lubricating and protective film on the cornea and conjunctiva. Their viscosity prolongs the time they remain on the eye and reduces evaporation. Artificial tears are actually medical devices because they do not induce pharmacological effects, but act physically.
Indications
Indications for use include:
- Insufficient production of lacrimal fluid (dry eyes).
- Eye irritation and inflammation, in conjunctivitis or keratitis.
- Tired, burning eyes.
- Improving the comfort of wearing contact lenses.
Dosage
According to the technical and directions for use. As a rule, the drops can be placed in the conjunctival sac of the eyes several times a day. Usually, application three to four times daily is sufficient. Application can be regular or as needed. See also under Administering eye drops. The single doses are intended for single use, according to the product information. Some are resealable and may be stored for up to 12 hours.
Active ingredients (selection)
Polymers used:
- Carmellose (carboxymethyl cellulose).
- Carbomers
- Dextran-70
- Hydroxypropyl Guar (HP Guar)
- Hyaluronic acid eye drops
- Hypromellose
- Macrogol 400
- Povidone
- Polyvinyl alcohol
Contraindications
Tear substitutes are contraindicated in case of hypersensitivity. Preparations without preservatives are also suitable for contact lens wearers. If eye drops with preservatives are used, lenses should be removed before use and reinserted after 15 minutes (there are exceptions). For complete precautions, refer to the drug label and directions for use.
Interactions
Other eye drops should be placed in the eye approximately 5 to 15 minutes apart. Eye ointments should be used last.
Adverse effects
Possible adverse effects include local reactions to the eye such as blurred vision and a burning sensation in the eye. Eye gels, in particular, can temporarily impair vision. Benzalkonium chloride, a preservative often used in eye drops, can cause adverse effects on the eye such as eye irritation, inflammation and corneal disease. Therefore, products without benzalkonium chloride should be used whenever possible. Alternative preservatives exist, such as Purite (oxychlorocomplex), which can be combined with lenses. The use of phosphate buffers to adjust the pH of eye drops is also criticized. The phosphate buffer, together with calcium, can form poorly soluble calcium phosphate crystals (hydroxyapatite). This can lead to cloudiness in the cornea, a condition known as calcification.
