Dry Eye Syndrome Disease Background

Introduction 

Dry eye syndrome (DES), also known as dry eye disease (DED), keratoconjunctivitis sicca (KCS) or dysfunctional tear syndrome, is a multifactorial disease of the ocular surface characterized by a loss of tear film hemostasis associated with ocular symptoms. 

Epidemiology 

Dry eye syndrome is a common condition that leads to varying degrees of eye discomfort, with a global prevalence of 5-50% depending on the diagnostic criteria used. Approximately 344 million people worldwide, 20 million in the United States (US), have DES, and this number is continually growing.  

Dry eye syndrome is noted to be more common in females and the Asian population. It is noted to increase in severity with age. In Asia, the prevalence rate is as high as 20-52.4%.

Pathophysiology 

The ocular symptoms of dry eye syndrome are secondary to several factors such as increased osmolarity of the tear film and inflammation of the ocular surface.

Tear hyperosmolarity may be due to reduced aqueous flow or excessive evaporation of tears. The tear film instability may be secondary to changes in function of the lipid layer, quality, quantity, and availability of tear fluid. Epithelial malfunction secondary to adverse environmental factors (eg low humidity, air conditioning or heating), ocular irritation or nerve impairment which may lead to inflammatory reactions. Dysfunction in the lacrimal glands, ocular surface, eyelids, meibomian glands, or associated sensory or motor nerves which may lead to DES causing changes in the volume, composition, distribution, and/or clearance of the tear film.

These symptoms may potentially damage the ocular surface. The presence of the hyperosmolar tear activates release of inflammatory mediators into the tears which may eventually result in decreased sensation of the cornea, decreased reflex activity, loss of goblet cells, and reduced production of mucin. Patients with moderate to severe DES may have reversible squamous metaplasia and punctate erosions of the ocular surface epithelium. In severe cases, DES may rarely cause ocular surface keratinization, microbial keratitis, corneal neovascularization, ulceration, perforation, scarring, or severe vision loss. 

Risk Factors 

Risk factors for DES include:

• Older age
• Female
• Estrogen hormone replacement therapy
• Androgen and vitamin A deficiency
• Antihistamine, antidepressants, anti-anxiety medications
• Decreased intake of omega-3 fatty acids
• Ocular conditions (eg seborrheic blepharitis, meibomian gland dysfunction, ocular rosacea)
• Connective tissue diseases (eg thyroid disease, Parkinson’s disease)
• Viral infections (eg hepatitis C infection, human immunodeficiency virus [HIV] infection)
• Radiation therapy
• Hematopoietic stem cell transplantation
• Laser-assisted in situ keratomileusis (LASIK) and refractive excimer laser surgeries

Classification 

Etiopathogenic Classification  

DES can be classified as aqueous tear-deficient dry eye or evaporative dry eye.  

In aqueous tear-deficient dry eye, also known as tear-deficient dry eye or lacrimal tear deficiency, the disease is secondary to the failure of lacrimal tear secretion. The condition is further subdivided into Sjögren syndrome, which is an autoimmune disorder, or non-Sjögren syndrome, which may be secondary to lacrimal gland insufficiency, lacrimal duct obstruction, or reflex hyposecretion.  

On the other hand, evaporative dry eye has normal secretory function but causes excessive loss of water from the exposed ocular surface. This may be secondary to intrinsic factors (eg meibomian gland dysfunction, eyelid aperture disorder or lid-globe incongruity, blink disorders) or extrinsic factors (eg ocular surface disease, contact lens wear, vitamin A deficiency, topical drug preservatives).  

A mixed condition may also be present where there is both aqueous tear-deficiency and evaporative dry eyes that is more pronounced in DES patients as the diseases progresses.  

Classification Based on Severity   

This classification system is based on the combination of signs and symptoms. However, this classification is considered indefinite as characteristics of the patients overlap at each level.  

Mild Dry Eye Syndrome (DES)  

Patients with mild DES have symptoms limited to irritation, itching, soreness, burning, or intermittent blurring of vision. Diagnosis is complicated due to inconsistent symptoms and signs, and the relatively low specificity and/or specificity of clinical tests.  

Moderate Drye Eye Syndrome (DES)  

Patients with moderate DES have increased discomfort and frequency of symptoms and more consistent visual dysfunction.  

Severe Dry Eye Syndrome (DES)  

Patients with severe DES have an increasing frequency of symptoms and visual dysfunction that may become constant.