RETINOPATHY
RETINOPATHY
Retinopathy is any damage to the
retina of the eyes, which may cause vision impairment. Retinopathy
often refers to retinal vascular disease, or damage to the retina caused by
abnormal blood flow. Age-related macular degeneration is technically
included under the umbrella term retinopathy but is often discussed as a
separate entity. Retinopathy, or retinal vascular disease, can be broadly
categorized into proliferative
and non-proliferative types.
Frequently, retinopathy is an ocular manifestation of systemic disease as seen
in diabetes or hypertension. Diabetes is
the most common cause of retinopathy in the U.S. as of 2008. Diabetic
retinopathy is the leading cause of blindness in working-aged people. It
accounts for about 5% of blindness worldwide and is designated a priority eye
disease by the World Health Organization.
Epidemiology
The
two most common causes of retinopathy include diabetic retinopathy and
retinopathy of prematurity. Diabetic retinopathy affects about 5 million people
and retinopathy of prematurity affect about 50,000 premature infants each year
worldwide. Hypertensive retinopathy is the next most common cause affecting
anywhere from 3 to 14% of all non-diabetic adults.
PATHOGENESIS & PATHOPHYSIOLOGY
The
development of retinopathy can be broken down into proliferative and
non-proliferative types. Both types cause disease by altering the normal blood
flow to the retina through different mechanisms. The retina is supplied by
small vessel branches from the central retinal artery Proliferative retinopathy
refers to damaged caused by abnormal blood vessel growth. Normally, angiogenesis is a natural part of
tissue growth and formation. When there is an unusually high or fast rate of angiogenesis,
there is an overgrowth of blood vessels called neovascularization. In the
non-proliferative type, abnormal blood flow to the retina occurs due to direct
damage or compromise of the blood vessels themselves.
CAUSES
Many causes of retinopathy may cause both
proliferative and non-proliferative types, though some causes are more
associated one type.
Non-proliferative
Retinopathy
Non-proliferative
retinopathy is often caused by direct damage or remodeling of the small blood
vessels supplying the retina. Many common causes of non-proliferative damage
include hypertensive retinopathy, Retinopathy of prematurity, Radiation
retinopathy, solar
retinopathy, and retinopathy associated with Sickle cell disease.
There
are three main mechanisms of damage in non-proliferative retinopathy: blood
vessel damage or remodeling, direct retinal damage, or occlusion of the blood
vessels. The first mechanism is indirect damage by altering the blood vessels
that supply the retina. In the case of hypertension, high pressures in the
system causes the walls of the artery to thicken, which effectively reduces the
amount of blood flow to the retina. This reduction in flow causes tissue
ischemia leading to damage. Atherosclerosis, or hardening and narrowing of
blood vessels, also reduces flow to the retina. The second mechanism is direct
damage to the retina usually caused by free radicals that causes oxidative
damage to the retina itself. Radiation, solar retinopathy, and retinopathy of
prematurity fall under this category. The third common mechanism is occlusion
of blood flow. This can be caused by either physically blocking the vessels of
the retinal artery branches or causing the arteries to narrow. Again, the end
result is reduced blood flow to the retina causing tissue damage. Sickle cell
disease compromises blood flow by causing blood to sludge, or thicken and flow
slowly, through the retinal arteries. Other disorders that cause hyperviscosity
syndrome may also cause blood sludging. Lastly, clots or central arterty thrombosisdirectly
blocks flow to the retina causing the cells to die.
Proliferative retinopathy
Is
the result of aberrant blood flow to the retina due to blood vessel overgrowth,
or neovascularization. These pathologically overgrown blood vessels are often
fragile, weak, and ineffective at perfusing the retinal tissues. These weak,
fragile vessels are also often leaky, allowing fluids, protein, and other
debris to leech out into the retina. They are also prone to hemorrhage due to
their poor strength. This makes proliferative types of retinopathy more risky
since vessel hemorrhaging often leads to vision loss and blindness. Many of the
causes mentioned in non-proliferative retinopathy may also cause proliferative
retinopathy at later stages. Angiogenesis and neovascularization tend to be a
later manifestation of non-proliferative retinopathy. Many types of
non-proliferative retinopathies result in tissue ischemia or direct retinal
damage. The body responds by trying to increase blood flow to damaged retinal
tissues. Diabetes mellitus, which causes diabetic retinopathy, is the most
common cause of proliferative retinopathy in the world.
Other
Causes;
Genetic
mutations are rare causes of certain retinopathies and are usually X-linked including
NDP family of genes causing
Norrie Disease, fever, and
Coats disease among others. There is emerging evidence that there may be a
genetic predisposition in patients who develop retinopathy of prematurity and
diabetic retinopathy. Trauma, especially to the head, and several diseases may
cause Purtscher's retinopathy
Diagnosis
Retinopathy
is diagnosed by an ophthalmologist or an optometrist during eye examination. Stereoscopic
fundus photography is the gold standard for the diagnosis of retinopathy.
Dilated fundoscopy, or direct visualization of the fundus, has been shown to be
effective as well.
SIGNS AND SYMPTOMS
Many
patients often do not have symptoms until very late in their disease course. Patients
often become symptomatic when there is irreversible damage.
- Vitreous hemorrhage
- Floaters or small objects that
drift through the field of vision
- Decreased visual acuity
- "Curtain falling" over
eyes
Treatment
Treatment is based on
the cause of the retinopathy and may include laser therapy to the retina. Laser
photocoagulation therapy has been the standard treatment for many types of
retinopathy. Evidence show that laser therapy is generally safe and improves
visual symptoms in sickle cell and diabetic retinopathy. In recent years targeting the pathway
controlling vessel growth or angiogenesis has been promising. Vascular
endothelia lgrowth factor (VEGF) seems to play a vital role in promoting
neovascularization. Using anti-VEGF drugs (antibodies to sequester the growth
factor), research have shown significant reduction in the extent of vessel
outgrowth. Evidence supports the use of anti-VEGF antibodies, such as bevacizumab
or pegaptanib seems to improve outcomes when used in conjunction with laser
therapy to treat retinopathy of prematurity. The evidence is poorer
for treatment of diabetic retinopathy. Use of anti-VEGF drugs did not appear to
improve outcomes when compared to standard laser therapy for diabetic
retinopathy.DOWNLOAD LINK
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