Dry Eye Syndrome (DES), also known as kerato conjunctivitis sicca is a multifactorial condition resulting from changes in tear composition and/or ocular surface. Characterized by chronic dryness of the cornea and conjunctiva, DES often causes symptoms such as burning, stinging, itching and photophobia and if untreated can result in the development of ocular surface abnormalities, potentially leading to loss of visual function. DES is a common disorder, thought to affect nearly 5 million Americans aged 50 years old and above; two-thirds of which are women. DES can be subdivided into two main classes based on etiology; aqueous tear-deficient dry eye or evaporative dry eye.
The tear film, which maintains eye moisture, consists of 3 layers. The outer lipid layer is produced by the meibomian glands and is comprised of cholesterols, fatty acids, and phospholipids, providing a smooth optical surface and preventing the evaporation of tears. The middle aqueous layer contains numerous essential nutrients supportive of the ocular surface environment. It is water based and includes components such as lysozyme, immunoglobulins, sodium and some soluble mucins. Finally, the innermost mucus layer, secreted principally by the conjunctival goblet cells is made up of components includingsilacic acid, hyaluronic acid, and various ocular mucins which attach to glycocalyx, anchoring the aqueous tear film to the corneal epithelium. Alterations in the composition, volume, clearance and /or distribution of the tear film can lead to DES. Such alterations can be caused by many different factors not limited to autoimmune disease, meibomian or lacrimal gland dysfunction, ocular surface irregularities, or structural abnormalities of the lid. Evaporative DES is most commonly caused by dysfunction of the meibomiangland causing lipid insufficiency or poor lipid distribution, leading to the disruption of tear film integrity and resultant decreased tear film stability and increased tear evaporation.
The pathogenesis of DES is incompletely understood, however inflammatory pathways activated in response to desiccating stress are recognized to play a pivotal role in the development and propagationof evaporative DES. Here, the induction of MAPK and NF-κB regulated proinflammatoy cytokines induces the activation and maturation of immature antigen presenting cells (APCs) which induce effector helper T cells that then travel to the ocular surface and release an array of proinflammatory mediators, amplifying preexisting inflammation and potentially contributing to the destruction of normal secretory function.
Management of DES most commonly includes the strategies and approaches to increase lubrication, minimize evaporative tear loss, stabilization of the tear film, enhancement of gland secretion and targeting the immune component of this common multifactorial disorder.
In conclusion, DES is a common disorder which can lead to visual impairment and profound effects on an individual’s quality of life. This disease can be subdivided into either aqueous tear-deficient or evaporative dry eye based on etiology, resulting from a variety of factors that causes changes in tear film composition and/or structural abnormalities leading to the activation of proinflammatory cascades which are thought to drive much of the pathology behind this disease.
Animation of the treatment of dry eye syndrome
Dry eye syndrome is a condition characterized by a decrease in the quality or quantity of the tear film that covers the surface of the eye. In this condition, a patient may experience visual disturbances as well as damage to the ocular surface. This medical animation highlights a treatment for dry eye syndrome that is thought to reestablish a healthy tear film and treat some of the symptoms associated with this condition.
This is an image of the mucin layer of the eye’s tear film, which is comprised of silicic acid, hyaluronic acid and various mucins which have various functions such as forming a viscoelastic matrix to protect the ocular surface and securing the tear layer to the microvilli and glycocalyx.
This is an image of the tear film, which is composed of three layers, the outer lipid layer, middle aqueous layer and the lower mucin layer.