The conjunctiva is the clear layer of tissue that lines the inner
eyelids (tarsal or palpebral conjunctiva)
and the eyeball itself (bulbar conjunctiva).
It extends from the eyelid margin to the edge of the cornea. Histologically,
the conjunctiva is composed of an epithelial layer that contains
goblet cells, a substantia propria layer that contains lymphatic
vessels, and a lymphoid layer that is active in generating immune
responses. The conjunctiva is normally clear, with a few visible
blood vessels supplied by the anterior ciliary artery. The vessels
become dilated when they are irritated (blood-shot eyes).
The conjunctiva is important in maintaining a normal tear film
in the eye. The tears are composed of 3 layers (Figure 27–1).
The bulk of the tear film is composed of the liquid
aqueous layer, which is secreted by the lacrimal glands. The
external surface of the tear film is composed of the lipid layer. This layer is formed by
lipids secreted by the meibomian glands in the eyelids. The lipid
layer maintains stability of the tear film and retards evaporation.
The basal layer of the tear film is the mucin
layer. This layer is secreted by the conjunctival goblet cells.
Its primary function is to promote adhesion between the tear film
and the eyeball and lubricate the eye. Abnormalities of any of these
layers may cause dysfunction of the tears, with secondary ocular
Inflammation of the conjunctiva due to allergies or infection
(pink eye) is one of the most common ocular problems encountered
The conjunctiva has a limited number of ways to respond to stimuli.
The most common is dilation of the conjunctival blood vessels, which
may occur as a reaction to external irritation (e.g., smoke), infection,
trauma, or inflammation. These conditions may also cause edema of
the conjunctiva, which produces a milky thickening of the conjunctival
tissue (chemosis) (Figure 27–2). If the conjunctiva is
diffusely damaged, the surfaces may scar. This can produce adhesion
of the conjunctiva between the globe and the inner lining of the
eyelid (symblepharon) (Figure 27–3). If a large area of
the conjunctiva is injured, tear film dysfunction may develop due
to loss of the mucin tear layer that is normally produced by the
conjunctival goblet cells. In this condition the tear production
is normal, but the tears do not function properly because they cannot
adhere to the eye.
Thickening (chemosis) and injection (engorged blood vessels)
of conjunctiva following blunt trauma (air bag).
Symblepharon (scar tissue) between tarsal (eyelid) and
bulbar (eyeball) conjunctiva following a chemical injury.