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Nervous System
pressure), opthalmoscopic visualization of the optic
nerve, and visual field testing.
The elevation in intraocular pressure in persons with
open-angle glaucoma is usually treated pharmacologically
or, in cases where pharmacologic treatment fails, by
increasing aqueous outflow through a surgically created
pathway. Drugs used in the long-term management of
glaucoma fall into five classes:
β
-adrenergic antagonists,
prostaglandin analogs,
α
-adrenergic agonists, carbonic
anhydrase inhibitors, and cholinergic agonists.
34,37
Most
glaucoma drugs are applied topically as eye drops.
Topical
β
-adrenergic antagonists, which are thought
to lower intraocular pressure by decreasing aqueous
humor production, are usually the drugs of first choice.
Prostaglandin analogs, which increase the outflow of
aqueous humor through the iris root and ciliary body,
are highly effective first-line or adjuvant agents.
34
The
α
-adrenergic agonists cause an early decrease in production
of aqueous humor by constricting the vessels supplying
the ciliary body. Carbonic anhydrase inhibitors reduce
the secretion of aqueous humor. Cholinergic drugs, which
exert their effects by increasing the effects of acetylcholine
(a postganglionic neurotransmitter for the parasympathetic
nervous system), increase aqueous outflow through
contraction of the ciliary muscle and pupillary constriction.
When a reduction in intraocular pressure cannot
be maintained through pharmacologic methods, laser
or surgical trabeculoplasty may become necessary.
34
With laser trabeculoplasty, the microburns created
by the laser treatment scar rather than penetrate the
trabecular meshwork, a process thought to enlarge the
outflow channels by increasing the tension exerted on
the trabecular meshwork. Cryotherapy, diathermy, and
FIGURE 38-12.
Optic nerve head in glaucoma.The anterior
part of the optic nerve is decompressed (“optic cupping”
arrows), and the blood vessels crossing the margin of the
optic nerve head are displaced to the nasal side.The fundus
appears dark because the eye of an African-American patient
contains numerous pigmented melanocytes in the choroid.
(From Klintworth GK.The eye. In: Rubin R, Strayer DS, eds.
Pathology; Clinicopathologic Foundations of Medicine. 6th ed.
Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams &
Wilkins; 2012:1410).
FIGURE 38-11.
(A)
Normally, aqueous humor, which is
secreted in the posterior chamber, gains access to the anterior
chamber by flowing through the pupil. In the angle of the
anterior chamber, it passes through the canal of Schlemm into
the venous system.
(B)
In open-angle glaucoma, the outflow
of aqueous humor is obstructed at the trabecular meshwork.
(C)
In angle-closure glaucoma, the aqueous humor encounters
resistance to flow through the pupil. Increased pressure in
the posterior chamber produces a forward bowing of the
peripheral iris, so that the iris blocks the trabecular meshwork.
Anterior
chamber
Pupil
Iris
Posterior chamber
Canal of Schlemm
Ciliary body
Trabecular meshwork
Cornea
A
Lens
B
C
