Dry eyes affect millions of people all around the world. This condition is more common in women after menopause, but it can affect both genders at all ages, including children.
Dry eye symptoms are well known to sufferers:
irritation
red eyes
light ipersensitivity
constant sensation of a foreign body in the eye.
In some cases, these symptoms can be misunderstood even by the same healthcare professionals who, due to the methods of description and the lack of specificity reported by the patient, often neglect or minimize them.
Dry eye syndrome (also known by the acronym DED, Dry Eye Disease or simply as Dry Eye) is a multifactorial pathology of the lacrimal system and the ocular surface that causes symptoms of ocular discomfort, visual disturbances and instability of the tear film with consequent potential damage of the ocular surface itself.
It is usually accompanied by tear film hyperosmolarity and ocular surface inflammation.
Tears play a decisive role in maintaining the integrity of the ocular surface, protecting it from the aggression of microorganisms and safeguarding the quality of vision.
The alteration, reduction or disappearance of the tear film can seriously damage the eye. This, along with other associated conditions, can lead to:
eye dryness
increased incidence of infections
corneal ulceration and perforations caused by reduced quantity and quality of tears.
The tear film protects the eye by washing away harmful chemicals and environmental contaminants from the ocular surface.
This protective film, much more complex than the common imagination, covers the surface of the eye and consists in three layers.
The outer or lipid layer is very thin and lipophilic. This layer, located on the surface of the tear film, is secreted by the meibomian glands located just behind the eyelashes inside the eyelids. This outer layer prevents the evaporation of water from the tear film.
Eyelid abnormalities and diseases, such as blepharitis, styes and chalazion, can cause increased evaporation of tears and potentially dry eye.
The middle or watery layer is secreted by the tear glands and makes up the majority of the tear film. This layer supplies the surface of the eye with oxygen and various nutrients as well as physiological hydration.
Sjogren's syndrome is a systemic disease characterized by dry eye and dry mouth, affecting the lacrimal gland, leading to a decrease in the aqueous component of tear secretion.
The inner layer of tears, or mucin, is secreted by goblet cells normally found on the surface of the eye. This layer coats the surface of the eye (epithelium) with a substance called mucin, which allows tears to adhere to the surface of the eye and in particular to the corneal microvilli.
The most common symptoms of dry eye include:
eye irritation pain
the sensation of grains of sand
decreased tolerance to contact lenses
an increased sensitivity to light.
In the early stages, symptoms may be intermittent, but they usually get worse over the course of the day.
There are many methods to study dry eye syndrome. The first and also the simplest is the Shirmer Test.
The test consists in inserting thin millimeter strips of bibulous paper behind the lower eyelids, in order to evaluate the quantity of tears produced by the patient. It is an examination to be performed before any other diagnostic procedure and with dimmed ambient light. It measures both basal (at rest) and reflex tear secretion. If the value is less than 10 mm the diagnosis is hyposecretion.
The Basal secretion test (Jones test) is a variant of the previous test. The difference is that a drop of local anesthetic is instilled in the eye and after 7 seconds the degree of imbibition of the paper strip is measured. By difference with the value found with this test from that obtained with the Shirmer test we obtain approximately the value of the reflex tear secretion. If these values are less than 5 mm they are to be considered pathological.
The Fluorescein Stain Test uses strips of special paper colored at one end with an orange dye and inserted behind the lower eyelid. Then, it is observed with cobalt blue light from the slit lamp. In this way it is possible to evaluate both the break up time, i.e. the breaking time of the tear film and, therefore, of its ability to coat the ocular surface; and the possible presence of areas of erosion of the cornea and conjunctiva resulting from dry eyes.
The Lissamine Green Test (Van Bijsterveld Test) consists in applying a strip of paper where the green dye is fixed and observing between the first and fourth minute, using the green light of the low intensity slit lamp. From here, a score is obtained linked to the quantity of corneo-conjunctival sectors colored in a more or less extensive punctiform way.