Dry eyes, also known as dry eye syndrome (DES), dry eye disease (DED), ocular surface disease (OSD), dysfunctional tear syndrome (DTS), and keratoconjunctivitis sicca (KCS), are among the most common reasons for a visit to an eye doctor. The definition of a dry eye according to the Tear Film and Ocular Surface Society (TFOS) Dry Eye Workshop II (DEWS II) is, "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 etiologic roles."
The tear film is approximately 2 to 5.5 µm thick over the cornea and comprises 3 main components. These components (lipid, aqueous, and mucin) are often described as layers, although this may oversimplify the tear film milieu.
The tear film is approximately 2 to 5.5 µm thick over the cornea. It is composed of 3 main components, often described as layers (although this may be an oversimplification of the tear film milieu):
Lipid layer: The most superficial layer; produced by the meibomian glands of the eyelids and functions to reduce the evaporation of tears
Aqueous layer: The middle layer and the thickest component of the tear film; produced by the lacrimal glands, located in the orbits and the accessory lacrimal glands (glands of Krause and Wolfring) in the conjunctiva. Aqueous fluid contains water, metabolites, electrolytes, peptides, proteins, etc.
Basal layer: Composed of mucins, or glycoproteins; predominantly produced by conjunctival goblet cells. Mucins enhance the spread of the tear film over the corneal epithelium through the regulation of surface tension.
Nomenclature and Terminology
DES and DED relate to a common ocular illness in which there is insufficient lubrication and moisture on the eye's surface. Numerous symptoms, such as dryness, irritation, burning, redness, and blurred vision, can be brought on by this illness. Even though the names are frequently used interchangeably, DED refers to a more comprehensive understanding of the disorder. It can be confusing because different medical practitioners and researchers use different terminologies.
DES
This term is frequently used informally to refer to inadequate tear production or poor tear quality, which causes ocular pain and associated symptoms. Patients and medical professionals frequently use it to characterize the disease.
DED
The multifaceted character of the ailment is better described by the more inclusive term DED. It recognizes that evaporative dry eye, aqueous deficit, and mixed etiologies are some underlying causes of dry eye, a complex and heterogeneous disease. DED covers a broader spectrum of clinical manifestations and causes.
Classification
DES is a broader term that emphasizes symptoms and a decline in tear quantity or quality rather than focusing on underlying causes in detail. DED acknowledges that the disorder has several facets and different subtypes. The 2017 TFOS DEWS II report offers a thorough categorization and in-depth explanation of dry eye illness. Inflammation, neurosensory abnormalities, and environmental triggers are just a few of the contributing elements the report considers when classifying DED into aqueous-deficient and evaporative subtypes.
Diagnosis and Treatment
Diagnostic procedures and therapies for DES and DED are comparable. A thorough eye exam that includes tests for tear film quality and quantity, a review of the ocular surface, and an evaluation of the patient's stated symptoms is frequently required for diagnosis. Artificial tears, lubricating eye drops, dietary changes, antiinflammatory drugs, and, in extreme circumstances, procedures or operations may all be used as treatments. The underlying cause and severity of the condition determine the best course of action.
Research
Over time, dry eye research has advanced, and our understanding of the condition has become more complex. In contemporary medical literature and research investigations, the term DED is used more frequently to reflect this thorough understanding. Inflammation, meibomian gland dysfunction, and the effect of the environment on the ocular surface have all been studied in recent DED studies. Researchers hope to advance patient care by utilizing the term DED to cover various contributing factors.
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