Generality
Artificial tears are sterile solutions, based on viscous substances, able to retain moisture on the surface of the eye; they are available in the form of eye drops, gels and ointments, which simulate the natural composition of tears.
Natural tears
Tears are essential to keeping the eye healthy. The tear film lubricates the ocular surface, reduces friction, provides nourishment and oxygen to the conjunctival epithelium and protects the eyes from any small foreign bodies, toxic substances and bacteria.
Tears are composed of water, carbohydrates, lipids, electrolytes, lysozymes (enzymes with bactericidal activity), lactoferrin (a protein that prevents or slows bacterial growth) and "binding" proteins.
The tear film of the eye (or precorneal film) has three distinct layers, from the outermost:
- Lipid layer : composed of fats, it is secreted by the meibomian glands. Cover the aqueous layer; it provides a hydrophobic barrier to prevent the tear film from coming out of the eye and helps maintain hydration of the ocular surface.
- Aqueous layer : secreted by the lacrimal glands, it is composed of water and other substances such as electrolytes, organic acids, amino acids and proteins. Reduces friction of eye and eyelid movements; promotes tear film diffusion, control of infectious agents and osmotic regulation.
- Mucous layer : it is secreted by the goblet cells of the conjunctiva and covers the cornea; making the surface otherwise hydrophobic hydrophilic.
The altered composition of the tear film and the lack or poor production of tears can have different consequences, including serious corneal lesions.
Artificial Tears and Dry Eyes
Artificial tears help to reconstitute and stabilize the tear film that covers the eye, alleviating the irritation and discomfort caused by dry keratoconjunctivitis (dry eye). If applied at regular intervals, artificial tears can generally control the problem in people who do not produce enough tears or when the tear film is unstable. Severe cases require more aggressive treatment, such as the instillation of artificial tears 10-12 times a day. Once the symptoms improve, you can use the product as needed, approximately three or four times a day. For moderate or severe forms of eye dryness, artificial tears can be integrated with other therapies.
Pharmaceutical composition and forms
Although it is impossible for artificial tears to perfectly replace their natural counterparts, the available products try to simulate the composition of at least one of the three layers of the tear film. Artificial tears are formulated based on water, salts and polymers, but do not contain the proteins found in natural ones. The products may contain carboxymethylcellulose, hydroxypropyl methylcellulose (HPMC or hypromellose), hydroxypropyl cellulose and hyaluronic acid. Hydroxypropyl cellulose and other thickening agents stabilize and thicken in the precorneal tear film, prolonging the residence time of the solution on the ocular surface. In addition to lubricating the eyes, some artificial tears contain electrolytes. These additives can promote cell healing on the surface of the eye.
Another important approach to formulating an excellent product is to try to imitate the biphasic nature of the tears, providing a lipid and an aqueous component, where the lipid substitute better stabilizes the tear film.
Another factor to consider is viscosity. Patients with mild dry eyes may prefer an aqueous solution, while those with severe dry eye may prefer a more viscous preparation, which remains on the longer cornea, decreases friction and lubricates more. The main side effect of gel and ointments is the temporary blurred vision.
Another element of differentiation between the drops is osmolarity. If this parameter is lower, some artificial tears can have a better effect on the ocular surface. The ingredients used to obtain a lower osmolarity are called osmoprotectors (example: L-carnitine and erythritol). These are absorbed by epithelial cells on the surface of the eye and dampen their response, preventing cellular damage from hyperosmolarity.
Furthermore, it is possible to distinguish two categories of artificial tears:
- With preservatives. These artificial tears are often available in multidose vials and contain chemicals (preservatives) that discourage the growth of bacteria once the package has been opened. However, preservatives can irritate the eyes, especially in the case of moderate or severe dry eyes.
- Preservative free. These artificial tears have fewer additives and are generally recommended if they are applied more than four times a day or in cases of moderate or severe eye dryness. Often, products without preservatives are available in single-dose vials.
As anticipated, lubricating ointments can offer more lasting relief than eye drops, but they can cause temporary blurred vision. For this reason, these products should be applied just before going to sleep.
Artificial tears are available without a prescription, but it is useful to consult the ophthalmologist to decide the best approach for the specific case, especially based on the origin and extent of the condition. There are many products with different ingredients and sometimes this vast choice on the market is confusing to the patient.
To select the product, it is important to consider:
- The underlying cause of dry eye (example: deficit in tear production or systemic disease);
- How often is the patient applying artificial tears: according to the severity of the disease and the dosage, is a product with or without preservatives more appropriate?
Note : some types of artificial tears contain preservatives such as benzalkonium chloride, which can produce toxic effects or hypersensitivity. The instillation of drops containing benzalkonium chloride for long periods of time could damage the front of the eye (ie it can cause corneal toxicity, inflammation and reduced production of tears). Therefore, if long-term artificial tears are used more than four times a day, it is better to use a product without preservatives or that does not contain, in particular, this preservative.
Types of artificial tears
The artificial tears designed to alleviate the symptoms of dry eye are mainly:
- Artificial tears with cellulose derivatives: they add viscosity to the fluid on the surface of the eye, helping to temporarily relieve the symptoms of dry eyes.
- Artificial tears based on glycerine : thanks to the water content, they help keep the eye moist.
- Tears containing hyaluronic acid : hyaluronic acid gives the product similar characteristics to artificial tears based on cellulose derivatives.
- Tears with polyethylene glycol and propylene glycol : they have a lower viscosity than cellulose-based products and create a protective layer to allow the damaged areas of the cornea to heal.
- Oil based tears : they contain oil (for example: mineral oil) and other ingredients in emulsion, which aim to stabilize the tear film. The oily part of the natural tear film may be deficient if conditions are present, such as a blepharitis or dysfunction of the meibomian gland.
Correct Use
How to use artificial tears
Although artificial tears are widely used, many people do not know the best way to use them. First, it is necessary to use the product exactly as indicated in the package insert or as prescribed by your doctor. Do not use in greater or lesser quantities or for longer than recommended.
To apply the eye drops:
- Tilt your head back slightly and lower your lower eyelid with your index finger to create a small pocket. Hold the dropper over the eye with the tip pointing down.
- Look up and instill the drops (usually one or two), then close the eyelids gently for a few moments, so that the solution can spread over the ocular surface.
To apply an ointment or gel:
- Tilt your head back slightly and lower your lower eyelid with your index finger.
- Squeeze the product along the lower eyelid, without touching the eye with the tip of the applicator. Look down and close your eyes for a few minutes.
- After opening the eyes, it is possible to have blurred vision for a short time, during which it is better to avoid driving or performing other activities that require complete visual acuity.
Wash hands thoroughly before and after using the product. Make sure not to touch the eye, eyelid, eyelashes, hand or any other surface with the tip of the dropper or tube, as they could lead to infection if contaminated. Since the eye lubricant is used as needed, if the patient forgets an application, he can recover as soon as possible, distancing himself from the next one. Do not use two or more doses, but always respect the quantities indicated by your doctor. If you wear contact lenses, you must remove them before instilling the drops in the eyes and wait at least 15 minutes before applying them again.
Interactions
For artificial tears, no interactions are reported. However, it is possible to take some precautions. Contact lens wearers must choose specific products that are compatible with these devices. In the case of simultaneous therapy with other eye drops, space the application of the different products by at least 5 minutes. This ensures that the drugs do not interfere with each other. If you are using both eye drops and eye ointment, apply the drops 10 minutes before the ointment.
If the product changes color or becomes cloudy, do not use it.
In case of eye pain, changes in vision, redness or irritation of the eye, or if the condition worsens or lasts more than 72 hours, stop using artificial tears and consult your doctor.
Contraindications
A documented contraindication of artificial tears is hypersensitivity to one of the components of the product.
Before starting the treatment, it is however necessary to take into consideration the following conditions and report them to your doctor, who can indicate if the product is appropriate:
- Eye infections or trauma;
- Use of contact lenses;
- Unusual allergic reaction to artificial tears, other drugs, foods, dyes or preservatives.
- Pregnancy;
- Breastfeeding.
Side effects
Possible adverse effects, which should be reported to the doctor as soon as possible, include:
- Eye pain;
- Changes in vision;
- Headache;
- Allergic reactions, such as skin rashes, itching or burning, difficulty breathing, swelling of the face, lips, tongue or throat;
- Irritation and redness, which progressively worsen or last for more than 72 hours.
If one of these signs occurs, the use of artificial tears must be stopped. Possible side effects of products containing hydroxypropyl cellulose include hyperemia, photophobia, stickiness of eyelashes, discomfort and irritation.
Less serious side effects of artificial tears, which do not require medical attention (however, to be reported to the doctor, if they persist or are bothersome) can be:
- Mild eye burn or temporary blurred vision after application;
- Itching or redness of the eyes;
- Tearing;
- Unpleasant taste in the mouth.
storage
Store artificial tears at room temperature (between 15 and 30 ° C), away from moisture and heat. Do not freeze. Keep the bottle or tube tightly closed. Once the product is opened, most experts recommend using it within 30 days. It is important to remember to keep this and all other medicines out of the reach of children, do not share them with other people and use artificial tears only for the prescribed indications.
