CHAPTER 20
Eye
407
The ganglion cells and their axons are part of the central nervous system. They cannot regenerate following severe damage.
Embryologically, the pigmented epithelium layer and the neural layers of the retina originate from different layers of the optic
vesicle. Therefore,
retinal detachment
may occur between the pigmented epithelium layer and the rest of the neural retina.
SYNOPSIS 20-1
Retinal Layers
(1)
Pigment epithelium layer
, a layer of cuboidal cells which are rich in melanin granules. This layer is important in absorbing
excess light and in esterifying vitamin A.
(2)
Photoreceptor (rods and cones) layer
, consists of inner and outer segments of the photoreceptor cells.
(3)
Outer limiting layer
, a plexus of junction complexes that joins the membranes of the photoreceptor cells and Müller
cells (retinal glial cells).
(4)
Outer nuclear layer
, contains nuclei of the photoreceptor cells (rods and cones).
(5)
Outer plexiform layer
, consists of axodendritic synapses between the axons of the photoreceptor cells and dendrites of
the bipolar and horizontal cells.
(6)
Inner nuclear layer
, contains nuclei of bipolar cells, horizontal cells, amacrine cells, and Müller cells.
(7)
Inner plexiform layer
, composed of axodendritic synapses between the bipolar cell axons, ganglion cell dendrites, and
processes of the amacrine cells.
(8)
Ganglion cell layer
, contains nuclei of the ganglion cells.
(9)
Nerve F
ber layer
, contains axons of the ganglion cells.
(10)
Inner limiting membrane
, the basement membrane of the Müller cells.
CLINICAL CORRELATIONS
Figure 20-16A.
Age-Related Macular Degeneration.
Age-related macular degeneration (ARMD)
is a degenerative eye
disease affecting the central portion of the retina. Symptoms include
blurred vision, distortion of straight lines, and worsening of color
vision. There are two forms:
exudative
(
wet
) and
nonexudative
(
dry
).
Wet ARMD
is characterized by the growth of new vessels from the
choroidal circulation and
serous fl uid leakage
from the new vessels.
This causes detachment of the retina and macula, producing a rapid
and irreversible loss of central vision. Treatment options include
laser photocoagulation, surgery, and drugs.
Dry ARMD
is char-
acterized by subretinal drusen deposits (focal eosinophilic material
arising from the
Bruch membrane
and lying between the pigment
epithelium and the Bruch membrane), and atrophy and degeneration
of the outer retina, including the retinal pigment epithelium, Bruch
membrane, and choriocapillaris. The causes of ARMD are not well
understood, but risk factors include age, smoking, family history,
hypertension, and ethnicity (higher in non-Hispanic Caucasians).
D. Cui
Pigment epithelium
Vitreous fluid-
filled space
Detached
retina
Photoreceptor
layer
Retinal
hole
Vitreous fluid
B
Figure 20-16
B
.
Retinal Detachment.
H&E,
3
62
Retinal detachment
is an eye condition in which the sensory retina
separates from the underlying retinal pigment epithelium and
choroid (see
red arrows
). It is categorized into three major types:
(1)
rhegmatogenous retinal detachment ([RRD]
illustrated) is the
most common; it occurs when
vitreous fl uid
leaks into the subreti-
nal space through a break in the retina; (2)
exudative
or
serous
detachment
occurs in association with infl ammation or a tumor;
(3)
traction detachment
occurs when scar tissue on the retina’s sur-
face contracts and causes the retina to separate from the retinal
pig-
ment epithelium
. Retinal detachment is a medical emergency that
can lead to permanent vision loss. Time is critical for surgical reat-
tachment of the retina, which will usually preserve vision. Symptoms
include fl ashes, fl oaters, and visual F eld distortion or loss. Treatment
options include laser photocoagulation, cryoretinopexy, vitrectomy,
and silicone oil repair.
J. Lynch
Choroid
Abnormal blood
vessels, leaking fluid
Bruch membrane
A
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