The Lacrimal System: Tear Production, Drainage & Functions
Anatomy and physiology of tear secretion (main and accessory glands), basal vs. reflex tearing, nasolacrimal drainage pathways, and how tears nourish and protect the cornea.
Article Table of Contents
1. Comprehensive Overview
The lacrimal apparatus consists of two coordinated systems: the secretory system (tear production) and the excretory system (tear drainage).
1. Tear Secretion: - Main Lacrimal Gland: Produces ~75% of aqueous tears; located in the superotemporal orbit beneath the brow, delivering tears via ~12 ducts into the superior conjunctival fornix. - Accessory Lacrimal Glands: Located in the conjunctiva, secreting mucin and lipid components essential for tear film stability. Tears are secreted in two modes: Basal Secretion (continuous, unperceived 24-hour lubrication) and Reflex Secretion (copious tearing triggered by irritation, inflammation, or emotion).
2. Tear Drainage: Tears enter the upper and lower puncta (1–2 mm openings at the medial lid margins), travel 8–10 mm through the canaliculi, collect in the Lacrimal Sac beside the nose, and pass down the 18 mm Nasolacrimal Duct into the nasal cavity and pharynx—explaining why patients taste eye drops in their throat.
3. Vital Functions of Tears: - Creates a smooth optical surface on the cornea for sharp light refraction. - Supplies oxygen and glucose to the avascular cornea and removes metabolic waste. - Defends against bacteria and viruses via lysozyme enzymes and antibodies. - Flushes away dust and foreign particles.
2. Symptoms & Warning Signs
If you observe any of the following symptoms repeatedly, an eye exam is strongly recommended:
- Fluctuating blurry vision and burning when the tear film is unstable (Dry Eye)
- Overflow tearing (epiphora) down the cheek when drainage pathways are blocked
3. Causes & Risk Factors
- 1High heat, wind, and air conditioning accelerate tear evaporation
- 2Punctal or nasolacrimal duct obstruction prevents normal nasal drainage
4. Treatments & Medical Management
5. Prevention & Daily Eye Care Advice
- Regular blinking, which acts as the mechanical pump for tear distribution and drainage
- Avoiding direct airflow from fans and air conditioners toward the eyes
6. When to Seek Emergency Eye Care
Visit an immediate eye emergency center if you experience any of the following critical indicators:
- ⚠Persistent overflow tearing onto the cheek or chronic burning and dryness
7. Frequently Asked Questions
Q:Why can we taste eye drops in our throat after putting them in the eye?
Because excess tears and eye drops drain through the puncta and nasolacrimal duct directly into the nasal cavity and back of the throat (pharynx).