Overview

Conjunctival sac capacity≈7–10 µL

Typical eye-drop volume≈30–50 µL

The palpebral conjunctiva is firmly attached to the tarsal plates and is vascular and red; the bulbar conjunctiva is loosely attached to the anterior sclera (Tenon capsule) and is transparent, so the white sclera and fine conjunctival vessels show through. The two are continuous at the superior and inferior fornices. The conjunctiva stops at the limbus, where its epithelium becomes continuous with the corneal epithelium — it does not cover the cornea. Medially lie the semilunar fold (plica semilunaris) and the lacrimal caruncle.

The epithelium is non-keratinised stratified columnar (stratified squamous near the lid margin and limbus) with abundant goblet cells that secrete the mucin layer of the tear film. The substantia propria contains lymphoid tissue (conjunctiva-associated lymphoid tissue, CALT). The accessory lacrimal glands of Krause and Wolfring lie in the fornices and upper tarsus.

The conjunctival sac is the space between lids and globe into which eye drops are instilled; its capacity is only ≈7–10 µL, so most of a 30–50 µL drop overflows or drains down the nasolacrimal duct (systemic absorption, e.g. of timolol).

Location: Lines the posterior surfaces of the eyelids and the anterior sclera up to the corneoscleral limbus.

Parts & subdivisions

Palpebral conjunctiva
Lines the eyelids; adherent to the tarsal plates; site of papillae and follicles in conjunctivitis.
Bulbar conjunctiva
Covers the anterior sclera loosely; transparent; ends at the limbus.
Fornices
Superior and inferior recesses where palpebral and bulbar parts meet; the lacrimal ductules open into the superolateral fornix.
Goblet cells
Mucin-secreting cells that make the tear film adhere to the hydrophobic corneal surface.

Anatomy

Innervation: Ophthalmic (V1) and maxillary (V2) branches — supratrochlear, infratrochlear, lacrimal, infraorbital and long ciliary nerves.
Arterial supply: Palpebral arcades and anterior ciliary arteries (from the ophthalmic artery).
Lymphatic drainage: Preauricular (parotid) and submandibular lymph nodes.
Histology: Non-keratinised stratified columnar/squamous epithelium with goblet cells over a loose vascular lamina propria containing lymphocytes.

Function

Protect the eye surface and allow friction-free movement of lids over the globe
Secrete mucin (goblet cells) and aqueous tears (accessory lacrimal glands)
Provide immune defence (CALT, IgA)

Clinical significance

Conjunctivitis

"Pink eye" — the commonest cause of a red eye. Viral (adenovirus; most common): watery discharge, follicles, tender preauricular lymph node, highly contagious. Bacterial (S. aureus, S. pneumoniae, H. influenzae): purulent discharge with lids stuck together. Allergic: bilateral itch, watery discharge, papillae, atopic history. In neonates: N. gonorrhoeae (hyperacute, days 2–5, can perforate the cornea) and Chlamydia trachomatis (days 5–14). Vision, pupils and cornea are normal in uncomplicated conjunctivitis — reduced vision, photophobia or pain suggest keratitis, uveitis or glaucoma.

Subconjunctival haemorrhage

Bright-red painless patch from rupture of a conjunctival vessel (coughing, straining, anticoagulation, hypertension); vision normal; resolves in 1–2 weeks.

Trachoma

Chronic Chlamydia trachomatis (serovars A–C) infection causing conjunctival scarring, trichiasis and corneal opacity — the leading infectious cause of blindness worldwide.

Compiled from standard anatomy and physiology references — see the Special Senses sources. For education only; not medical advice.