08/12/2025
Tear System & Function
Your eyes have a “tear-making team” — the lacrimal glands, eyelids, meibomian glands, cornea, conjunctiva, and their nerves. They work together to keep your eyes moist, healthy, and your vision clear.
The tear film has three layers:
1. Mucous layer – Closest to the eye; made by goblet cells; acts like a slippery cushion, traps dust and germs.
2. Aqueous layer – The watery middle part; made by lacrimal glands; carries nutrients, oxygen, antibacterial agents, and helps healing.
3. Lipid layer – The oily top layer; made by meibomian glands; stops tears from drying too quickly and keeps the surface smooth.
The mucous and aqueous layers actually blend together into one “mucoaqueous” layer, thicker near the eye and thinner toward the air.
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Dry Eye Disease (DED):
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Dry eye happens when the tear system loses balance, leading to unstable tears, inflammation, and sometimes nerve problems.
It can be caused by:
• Aqueous tear deficiency – Not enough watery tears.
• Evaporative dry eye – Tears dry out too quickly.
Often, both happen together.
Examples: Contact lens wearers may blink less or incompletely, causing tears to evaporate, and some medicines can reduce tear production further.
Why it matters:
Dry eye can cause discomfort, blurred vision, and, in severe cases, damage to the eye’s surface, scarring, or even vision loss.
Causes of Dry Eye Disease (DED)
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1. Aqueous tear deficiency – Not enough watery tears
• Primary: Aging, born without tear glands, rare nerve disorders
• Secondary:
• Tear gland damage from disease (sarcoidosis, lymphoma, AIDS, hepatitis C) or surgery
• Blocked tear ducts
• Scarring from infections (trachoma), autoimmune diseases, chemical injury, graft-versus-host disease
• Nerve problems that reduce tear reflex (eye surgery, nerve injury, contact lenses, diabetes)
• Nerve or muscle signal problems (parasympathetic damage, certain medications)
• Sjögren’s syndrome: Autoimmune disease damaging tear and saliva glands (primary form or secondary to other autoimmune diseases like rheumatoid arthritis and lupus)
2. Evaporative dry eye – Tears dry out too quickly
• Lid-related:
• Meibomian gland problems (often linked to skin conditions like rosacea or dermatitis)
• Medications (e.g., isotretinoin)
• Eyelid shape issues, thyroid eye disease, contact lenses
• Low blink rate (e.g., Parkinson’s disease)
• Ocular surface-related:
• Low blink rate during reading, computer work, or TV
• Surface damage from vitamin A deficiency, certain eye drops, allergies
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Impact
• Can make daily activities (reading, driving, computer work, TV) uncomfortable
• Linked to higher rates of depression and anxiety, especially in primary Sjögren’s
• Some people have severe symptoms with little visible eye damage, while others have damage but few symptoms
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Risk Factors
• Non-modifiable: Age, female s*x, Asian ethnicity, autoimmune/connective tissue diseases, androgen deficiency
• Modifiable: Computer use, low humidity, pollution, certain medications, hormone therapy, meibomian gland dysfunction
• Probable links: Diabetes, rosacea, thyroid disease, psychiatric conditions, vitamin A deficiency, refractive surgery, allergies
• Less certain: Hispanic ethnicity, menopause, acne, smoking, alcohol, pregnancy, certain infections, Botox use.