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the cause of neovascularization is uncertain, research
links the process with a vascular endothelial growth fac-
tor (VEGF) produced by the lining of blood vessels.
25–27
Hypoxia is a key regulator of VEGF-induced retinal
neovascularization. It is likely that other growth factors
and signaling systems are also involved.
Opacities
represent a loss of retinal transparency due
to hemorrhages, exudates, cotton-wool spots, edema,
and tissue proliferation. The development of exudates
often results in the destruction of the underlying retinal
pigment and choroid layer.
Cotton-wool patches
are ret-
inal opacities with hazy, irregular outlines. They occur
in the nerve fiber layer of the retina and are associated
with retinal trauma, severe anemia, papilledema, and
diabetic retinopathy.
Diabetic Retinopathy.
Diabetic retinopathy is one
of the leading causes of blindness in the Western
world, particularly among individuals of working
age.
6,25–28
Chronic hyperglycemia, hypertension,
hypercholesteremia, and smoking are all risk factors for
the development and progression of the disorder. People
with type 1 (insulin-dependent) diabetes do not usually
develop the disorder until at least 3 to 5 years after the
onset of the disease, whereas those with type 2 diabetes
may have retinopathy as a presenting symptom at the
time of diagnosis.
25
Diabetic retinopathy can be divided into two types:
nonproliferative (or background) and proliferative.
6,25
Nonproliferative
retinopathy is confined to the retina.
It involves engorgement of the retinal veins, thickening
of the capillary endothelial basement membrane, and
development of capillarymicroaneurysms (Fig. 38-8A,B).
Small intraretinal hemorrhages may develop and
microinfarcts may cause cotton-wool spots and leakage
of exudates. The most common cause of decreased
vision in persons with background retinopathy is
macular edema. The edema is caused primarily by the
breakdown of the blood-retina barrier at the level of
the capillary endothelium, allowing leakage of fluid and
plasma constituents into the surrounding retina.
Proliferative diabetic retinopathy
represents a more
severe retinal change than background retinopathy
(Fig. 38-8C,D). It is characterized by formation of new
fragile blood vessels (i.e., neovascularization) at the
optic disk and elsewhere in the retina, which is often the
FIGURE 38-8.
(A)
Nonproliferative (background) retinopathy showing microaneurysms.
(B)
Ocular
fundus of a patient with background diabetic retinopathy. Several yellowish “hard” exudates (which
are rich in lipids) and several relatively small retinal hemorrhages are present.
(C)
Proliferative
retinopathy.
(D)
Ocular fundus in a patient with proliferative retinopathy. A vascular frond (branching
pattern of preretinal neovascularization) has extended anterior to the retina. (B and D from Klintworth
GK.The eye. In: Rubin R, Strayer DS, eds. Rubin’s Pathology: Clinicopathologic Foundations of
Medicine. 6th ed. Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams &Wilkins; 2012:1403.)
A
C
B
D
