C h a p t e r 3 8
Disorders of Special Sensory Function: Vision, Hearing, and Vestibular Function
965
first detectable sign of diabetic retinopathy. These vessels
grow in front of the retina along the posterior surface of
the vitreous or into the vitreous. They threaten vision in
two ways. First, they often leak blood into the vitreous
cavity and decrease visual acuity. Second, they attach
firmly to the retinal surface and the posterior surface of
the vitreous chamber, such that normal movement of the
vitreous humor may exert a pull on the retina, causing
retinal detachment and progressive blindness.
Current guidelines recommend that persons with
diabetes have yearly eye examinations.
27
Personswith any
level of macular edema, severe nonproliferative diabetic
retinopathy, or any proliferative retinopathy require
the prompt care of an ophthalmologist experienced in
the management and treatment of diabetic retinopathy.
Women with preexisting diabetes who plan to become
pregnant or are pregnant should have a comprehensive
eye examination and be counseled about the risk for
initiation or progression of diabetic retinopathy.
Preventing diabetic retinopathy from developing
or progressing is considered the best approach to pre-
serving vision. Growing evidence suggests that careful
control of blood glucose levels in persons with diabetes
mellitus may retard the onset and progression of reti-
nopathy. There also is a need for intensive management
of hypertension and hyperlipidemia, both of which have
been shown to increase the risk of diabetic retinopathy
in persons with diabetes.
28
Treatment strategies for diabetic retinopathy include
laser photocoagulation applied directly to leaking
microaneurysms and grid photocoagulation with a
checkerboardpatternof laserburnsappliedtodiffuseareas
of leakage and thickening. Because laser photocoagulation
destroys the proliferating vessels and the ischemic retina,
it reduces the stimulus for further neovascularization.
Intravitreal injections of anti-VEGF agents are also
being used to reduce active neovascularization and
vitreous hemorrhage.
28
Vitrectomy may be used for
removing vitreous hemorrhage and severing vitreoretinal
membranes that develop.
Hypertensive Retinopathy.
As with other blood
vessels in the body, the retinal vessels undergo changes
in response to chronically elevated blood pressure. In
the initial, vasoconstrictor stage, there is vasospasm
and an increase in retinal arterial tone because of local
autoregulatory mechanisms. On ophthalmoscopy, this
stage is represented by a general narrowing of the retinal
arterioles. Persistently elevated blood pressure results in
the compensatory thickening of arteriolar walls, which
effectively reduces capillary perfusion pressure.
29
With
severe uncontrolled hypertension, there is disruption of
the blood-retina barrier, necrosis of smooth muscle and
endothelial cells, exudation of blood and lipids, and
retinal ischemia. These changes are manifested in the
retina by microaneurysms, intraretinal hemorrhages, hard
exudates, and cotton-wool patches. Swelling of the optic
disk may occur at this stage and usually indicates severely
elevated blood pressure (malignant hypertension). Elderly
persons often have more rigid vessels that are unable to
respond to the same degree as those in younger individuals.
Retinal Detachment
Retinal detachment involves the separation of the
neurosensory retina from the pigment epithelium. The
disorder, which is one of most time-critical events seen
in an emergency department, occurs when traction on
the inner sensory layer or a tear in this layer allows
fluid, usually vitreous, to accumulate between the two
layers of the retina.
6,23,30
There are three types of retinal
detachments: exudative, traction, and rhegmatogenous.
Exudative Detachment.
Exudative (or serous) retinal
detachment results from the accumulation of serous or
hemorrhagic fluid in the subretinal space due to severe
hypertension, inflammation, or neoplastic effusions.
It usually resolves with successful treatment of the
underlying disease and without visual impairment.
Traction Retinal Detachment.
Traction retinal deat-
tachment
occurs with mechanical forces on the retina,
usually mediated by fibrotic tissue, resulting from previ-
ous hemorrhage (e.g., from diabetic retinopathy), injury,
infection, or inflammation. Intraocular surgery such as
cataract extraction may produce traction on the periph-
eral retina that causes eventual detachment months or
even years after surgery. Correction of traction retinal
detachment requires disengaging scar tissue from the
retinal surface, and vision outcomes are often poor.
Rhegmatogenous Detachment.
Rhegmatogenous
detachment, themost common type of retinal detachment,
is a full thickness break (“rhegma”) in the sensory retina,
with the passage of liquefied vitreous through the break
into the subretinal space. Although typically an acute
event, detachment is a consequence of lifelong liquefaction
of the vitreous humor, and is highly age-dependent with
27% of patients in their seventies and 63% in their
eighties.
30
As the collagenous and mucopolysaccharide
matrix of the vitreous humor begins to liquefy and shrink,
it pulls away from the retinal surface. Rhegmatogenous
detachment occurs when the liquid vitreous enters
the subretinal space through a retinal tear (Fig. 38-9).
Detachment of the neural retina from the retinal pigment
layer separates the visual receptors from their major
blood supply, the choroid. If retinal detachment continues
for some time, permanent destruction and blindness of
that part of the retina occur. Persons with high grades of
myopia or nearsightedness may have abnormalities in the
peripheral retina that predispose to sudden detachment.
In moderate to severe myopia, the anteroposterior length
of the eye is increased, and the retina tends to be thinner
and more prone to formation of a hole or tear.
30
As a
result, there is greater vitreoretinal traction, and posterior
vitreous detachment may occur at a younger age than in
persons without myopia.
Clinical Manifestations.
The primary symptom
of retinal detachment is painless changes in vision.
Commonly, flashing lights or sparks, followed by
small floaters or spots in the field of vision, are early
symptoms. As detachment progresses, the person
