DƯỢC LÍ Goodman & Gilman's The Pharmacological Basis of Therapeutics 12th, 2010

1776
SECTION IX
SPECIAL SYSTEMS PHARMACOLOGY
A
ANTERIOR
SEGMENT
POSTERIOR
SEGMENT
B
anterior
chamber
posterior
chamber
zonule
canal of Schlemm
(Schlemm’s canal)
scleral
spur
lens
trabecular
meshwork
conjunctiva
zonule
choroid
sclera
Cornea
retina
optic disk
limbus pupil cornea anterior chamber
iris
angle
episcleral
veins
posterior
lens
chamber
epithelium
Bowman’s membrane
stroma
Descemet’s membrane
endothelium
optic nerve
ciliary process
ciliary muscle
ciliary epithelium
pars plana
Ciliary
body
ciliary
body
vitreous
retinal
arterioles
and veins
central retinal
artery and vein
canal of
Schlemm
conjunctival
epithelium
trabecular
meshwork
Tenon’s
capsule
+
episclera
zonular
fibers
sclera
Figure 64–3. A. Anatomy of the eye. B. Enlargement of the anterior
segment, revealing the cornea, angle structures, lens, and
ciliary body. (Adapted with permission from Riordan-Eva P.
Anatomy and embryology of the eye. In, Vaughan & Asbury’s
General Ophthalmology, 17th ed. (Riordan-Eva P, Whitcher JP,
eds.) McGraw-Hill, New York, 2008. Copyright © 2008 by The
McGraw-Hill Companies, Inc. All rights reserved.)
parasympathetic and sympathetic nerves. Differences in iris color
reflect individual variation in the number of melanocytes located
in the stroma. Individual variation may be an important consideration
for ocular drug distribution due to drug-melanin binding (see
“Distribution”). The posterior surface of the iris is a densely pigmented
bilayer of epithelial cells. Anterior to the pigmented
epithelium, the dilator smooth muscle is oriented radially and is
innervated by the sympathetic nervous system (Figure 64–4),
which causes mydriasis (dilation). At the pupillary margin, the
sphincter smooth muscle is organized in a circular band with
parasympathetic innervation, which, when stimulated, causes miosis
(constriction). The use of pharmacological agents to dilate
normal pupils (i.e., for clinical purposes such as examining the
iris
optic
nerve
optic
chasm
optic
tract
lateral
geniculate
body
optic
radiation
visual
cortex
motor center
in occipital cortex
Edinger-Westphal
nuclei and
nuclei of Perlia
ocular fundus) and to evaluate the pharmacological response of
the pupil (e.g., unequal pupils, or anisocoria, seen in Horner’s syndrome
or Adie’s pupil) is summarized in Table 64–2. Figure 64–5
provides a flowchart for the diagnostic evaluation of anisocoria.
Ciliary Body. The ciliary body serves two very specialized roles in the
eye:
• secretion of aqueous humor by the epithelial bilayer
• accommodation by the ciliary muscle
inferior
cilio-spinal
sympathetic
center
hypothalamic
sympathetic
center
The anterior portion of the ciliary body, called the pars plicata,
is composed of 70-80 ciliary processes with intricate folds. The posterior
portion is the pars plana. The ciliary muscle is organized into outer
longitudinal, middle radial, and inner circular layers. Coordinated contraction
of this smooth muscle apparatus by the parasympathetic nervous
system causes the zonule suspending the lens to relax, allowing the
lens to become more convex and to shift slightly forward. This process,
known as accommodation, permits focusing on near objects and may
be pharmacologically blocked by muscarinic cholinergic antagonists,
through the process called cycloplegia. Contraction of the ciliary muscle
also puts traction on the scleral spur and hence widens the spaces
within the trabecular meshwork. This latter effect accounts for at least
some of the IOP-lowering effect of both directly acting and indirectly
acting parasympathomimetic drugs.
Lens. The lens, a transparent biconvex structure, is suspended by
zonules, specialized fibers emanating from the ciliary body. The lens
is ~10 mm in diameter and is enclosed in a capsule. The bulk of the
b
a
cervical
sympathetic
nerve
ciliary
ganglion
parasympathetic
fibers of
oculomotor
nerve
superior
cervical
sympathetic
ganglion
Figure 64–4. Autonomic innervation of the eye by the sympathetic
(a) and parasympathetic (b) nervous systems. (Adapted with permission
from Wybar KC, Kerr-Muir M. Bailliere’s Concise
Medical Textbooks, Ophthalmology, 3rd ed. Bailliere Tindall,
New York, 1984. Copyright © Elsevier.)