Dry eye is a multifactorial disease of the ocular surface characterized by a loss of homeostasis of the tear film, and accompanied by ocular symptoms, in which tear film instability and hyperosmolarity, ocular surface inflammation and damage, and neurosensory abnormalities play etiological roles. - TFOS DEWS II definition - 2017.
Ocular discomfort (burning, sandy-gritty feeling, difficulty in opening the eyelids, especially when waking-up), visual disturbances (blurred vision, photophobia), tear film instability with potential damage to the ocular surface.
Medical treatment should be aimed at reducing or eliminating, where possible, the trigger factors of the pathology and to reduce the discomfort that this condition determines. Usually it is recommended a symptomatic treatment, which involves the use of eye drops or gel whose composition is similar to tears, the so-called "artificial tears".
The "dry eye" syndrome, referred to as "keratoconjunctivitis Sicca" (in medical language), is a multifactorial disease that affects the tear film and ocular surface, causing symptoms of discomfort, visual disturbances, tear film instability with potential damage to the ocular surface. It is accompanied by increased osmolarity of the tear film and ocular surface inflammation.
The tear film is a film that covers the conjunctival-corneal surface and constitutes the interface between the eye and the external environment. It consists of three distinct layers: lipidic, aqueous and mucous.
The aqueous part of the tear film is the most abundant and contains numerous proteins and electrolytes, including lysozyme with antibacterial properties. It is produced by the lacrimal glands.
The tear film performs several functions:
- it lubricates the eye, creating a smooth surface on the cornea over which the eyelids can easily slide.
- it nourishes the cornea, as it is devoid of blood vessels (avascular tissue) and receives nutrients and oxygen through the tear film.
- it protects the eye from bacterial and viral infections and removes waste substances
Based on its causes it is possible to distinguish two main forms of dry eye: 1) hyposecretion forms; 2) evaporation forms.
Among the hyposecretion forms, in which there is reduced lacrimal glands functioning, are the forms related to autoimmune diseases such as Sjögren's syndrome, first and foremost, but also rheumatoid arthritis, systemic lupus erythematosus, polyarteritis nodosa, Wegener's Granulomatosis, systemic sclerosis and other connective tissue diseases.
Then there are the "non Sjögren" hyposecretive dry eye forms, the most important of which is related to ageing.
Dry eye from excess evaporation can be classified on the basis of the conditions that determine it, in "intrinsic" (e.g. in case of dysfunction of meibomian glands or eyelid and orbital anomalies) and "extrinsic" (due to the use of contact lenses or topical medications with preservatives; eye diseases such as allergies and conjunctivitis; vitamin A deficiency).
The main risk factors can be summarised as follows:
1. Age: ageing is the cause of a progressive deterioration of the lacrimal glands.
2. Gender: women between 40 and 60 years are most affected by dry eye, probably because of the new hormonal balance after the menopause.
3. Use of certain medications: hormones, immunosuppressants, antihypertensives, antihistamines, antidepressants, and others..
4. Climatic-environmental factors: air conditioners, dry climate, cigarette smoking, wind, smog.
5. Prolonged use of computers and television.
6. Nutritional deficiency: insufficient intake of vitamin A.
7. Use of contact lenses. In this respect it was found that the use of any type of contact lenses leads to alterations of the surface of the eye and of the tear film. The magnitude of these effects varies according to the material of the lens, the way of use and the characteristics of the wearer. Silicone Hydrogel lenses have generally less detrimental effects. The risk of infections and corneal inflammation remains high, especially in the case of frequent night wearing of the lenses. In the case of prevalent daytime wearing , ocular surface damage may also be caused by using some solutions for daily cleaning of the lenses, to which the eye can be or become particularly sensitive.
In recent years, dry eye, like other eye diseases such as glaucoma and Keratoconus has been associated with oxidative stress. The surface of the eye is also particularly exposed to environmental agents (wind, changes in temperature, ultraviolet) and irritant agents that make it vulnerable to oxidative stress. Mechanical factors such as the use of contact lenses or eye surgery can also be causes of oxidative stress to the surface of the eye.
The patients effected by dry eye may have a variety of symptoms, such as burning, sandy-gritty feeling, difficulty in opening the eyelid, especially waking-up, blurred vision, photophobia (light sensitivity), pain (in severe cases). These symptoms are often accompanied by clinical signs such as: redness, mucous hyposecretion, pain of the corneal-conjunctival epithelium.
The dry eye syndrome is a very common pathology whose diagnosis can be made using several tests, some of which are used to diagnose the qualitative alterations of the tear film (such as the tear break-up time test), while others measure the quantities of tearing deficiency (such as the Schirmer's test).
There is also a test to diagnose dry eye by measuring the tear osmolarity: an increase of this parameter indicates the presence of dry eye.
Most of the dry eye forms tends to become chronic and recurrent. Therefore, therapy should be aimed primarily at reducing or eliminating, where possible, the triggering factors of the disease and to reduce the discomfort that this condition causes, in order to improve the quality of life of the patient.
Normally it is a symptomatic treatment which involves the use of eye drops or gel whose composition is similar to tears, the so-called "artificial tears", with lubricant and moisturising properties.
Recently it has been considered important using artificial tears with antioxidant properties.
Self-prescription of artificial tears is strongly advised against, whereas it is recommended to undergo a visit by a ophthalmologist for an accurate diagnosis and for the prescription of an appropriate therapy.
In addition, it is preferable to use preservative-free artificial tears because they, as a result of prolonged use of products that contain preservatives, could damage the surface of the already compromised eye.