Dry Eye

Definition of Dry Eye Disease (DED)

The Tear Film & Ocular Surface Society (TFOS) Dry Eye Workshop II (DEWS II, 2017) defines dry eye as:

"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."

Classifications of Dry Eye Disease

Dry eye can be classified based on etiology, pathophysiology, and severity

1. Based on Etiology (Primary Cause)
(A) Aqueous-Deficient Dry Eye (ADDE)

Cause: Reduced tear production by lacrimal glands.

Subtypes:

• Sjögren’s syndrome-associated (autoimmune destruction of lacrimal glands).
• Non-Sjögren’s (age-related, lacrimal gland dysfunction, medications, post-radiation, etc.).

(B) Evaporative Dry Eye (EDE)

Cause: Excessive tear evaporation due to lipid layer deficiency.

Subtypes:

• Meibomian gland dysfunction (MGD) (most common).
• Low blink rate (e.g., prolonged screen use, Parkinson’s).
• Exposure-related (e.g., lagophthalmos, thyroid eye disease).

(C) Mixed Dry Eye

• Combination of ADDE + EDE* (most common in clinical practice).

Signs and symptom

• A stinging, burning or scratchy sensation in your eyes
• Stringy mucus in or around your eyes
• Sensitivity to light
• Eye redness
• A sensation of having something in your eyes
• Difficulty wearing contact lenses
• Difficulty with nighttime driving
• Watery eyes, which is the body's response to the irritation of dry eyes
• Blurred vision or eye fatigue

Causes

Dry eyes are caused by a variety of reasons that disrupt the healthy tear film. Your tear film has three layers: fatty oils, aqueous fluid and mucus. This combination usually keeps the surface of your eyes lubricated, smooth and clear. Problems with any of these layers can cause dry eyes.

Reasons for tear film dysfunction are many, including hormone changes, autoimmune disease, inflamed eyelid glands or allergic eye disease. For some people, the cause of dry eyes is decreased tear production or increased tear evaporation.

Tear glands

The tear glands located above each eyeball, called the lacrimal glands, continuously supply tear fluid that's wiped across the surface of your eye each time you blink your eyelids. Excess fluid drains through the tear ducts into the nose.

Decreased tear production

Dry eyes can occur when you're unable to produce enough liquid tears, also called aqueous fluid. The medical term for this condition is  keratoconjunctivitis sicca.

Risk Factors

Factors that make it more likely that you'll experience dry eyes include:

• Being older than 50. Tear production tends to diminish as you get older. Dry eyes are more common in people over 50.
• Being a woman. A lack of tears is more common in women, especially if they experience hormonal changes due to pregnancy, using birth control pills or menopause.
• Eating a diet that is low in vitamin A, which is found in liver, carrots and broccoli, or low in omega-3 fatty acids, which are found in fish, walnuts and vegetable oils.
• Wearing contact lenses or having a history of refractive surgery.

Common causes of increased tear evaporation include

• Posterior blepharitis (meibomian gland dysfunction)
• Blinking less often, which tends to occur with certain conditions, such as Parkinson's disease; or when you're concentrating during certain activities, such as while reading, driving or working at a computer
• Eyelid problems, such as the lids turning outward (ectropion) and the lids turning inward (entropion)
• Eye allergies
• Preservatives in topical eye drops
• Wind, smoke or dry air
• Vitamin A deficiency

Common causes of decreased tear production include

Aging

Certain medical conditions including Sjogren's syndrome, allergic eye disease, rheumatoid arthritis, lupus, scleroderma, graft vs. host disease, sarcoidosis, thyroid disorders or vitamin A  eficiency

Certain medicines

Including antihistamines, decongestants, hormone replacement therapy, antidepressants, and medicines for high blood pressure, acne, birth control and Parkinson's disease

Corneal nerve desensitivity

Caused by contact lens use, nerve damage or laser eye surgery, though symptoms of dry eyes related to this procedure are usually temporary

Increased tear evaporation

The oil film produced by small glands on the edge of your eyelids (meibomian glands) might become clogged. Blocked meibomian glands are more common in people with rosacea or other skin disorders

Prevention

If you experience dry eyes, pay attention to the situations that are most likely to cause your symptoms. Then find ways to avoid those situations in order to prevent your dry eyes symptoms.

For instance:

• Avoid air blowing in your eyes. Don't direct hair dryers, car heaters, air conditioners or fans toward your eyes.
• Add moisture to the air. In winter, a humidifier can add moisture to dry indoor air.
• Consider wearing wraparound sunglasses or other protective eyewear. Safety shields can be added to the tops and sides of eyeglasses to block wind and dry air. Ask about shields where you buy your eyeglasses.
• Take eye breaks during long tasks. If you're reading or doing another task that requires visual concentration, take periodic eye breaks. Close your eyes for a few minutes. Or blink repeatedly for a few seconds to help spread your tears evenly over your eyes.
• Be aware of your environment. The air at high altitudes, in desert areas and in airplanes can be extremely dry. When spending time in such an environment, it may be helpful to frequently close your eyes for a few minutes at a time to minimize evaporation of your tears.