The tear film is the thin fluid layer, a few micrometres thick, that covers the cornea and conjunctiva. It is usually described as an outer lipid layer from the meibomian glands, a middle aqueous layer from the lacrimal glands, and an inner mucin layer from conjunctival goblet cells. It is renewed with every blink.
| Location | Surface of the cornea and conjunctiva, with a reservoir in the lid margins (tear menisci) |
|---|---|
| Parts |
|
| Nerve Supply | Corneal sensory nerves (CN V1) driving reflex secretion; Parasympathetic fibres to the lacrimal gland |
| Blood Supply | Derived from secretions of glands supplied by the lacrimal and palpebral arteries |
Keeps the eye surface moist and smooth for clear vision, supplies oxygen to the cornea, washes away debris and fights infection.
A smooth tear film is the first refracting surface of the eye, so an unstable film causes blurred, fluctuating vision. Dry eye disease is very common and can be aqueous-deficient, evaporative or both. Tear break-up time and the Schirmer test assess tear quality and quantity. Screen use reduces blink rate and worsens symptoms.
Loss of tear film stability or volume causing burning, grittiness and blurred vision. It is linked to age, screen use, meibomian gland dysfunction and autoimmune disease.
Overflow of tears onto the cheek from overproduction (often reflex from dry eye) or blocked drainage.
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