Retinopathy

Retinopathy is a noninflammatory disease of the retina.  With treatment, vision loss may be slowed or halted.

Retinopathies are divided into two broad categories, simple or nonproliferative retinopathies and proliferative retinopathies.  The simple retinopathies include the defects identified by bulging of the vessel walls, by bleeding into the eye, by small clumps of dead retinal cells called cotton wool exudates, and by closed vessels.  This form of retinopathy is considered mild.  The proliferative – or severe – forms of retinopathies include the defects identified by newly grown blood vessels, by scar tissue formed within the eye, by closed-off blood vessels that are badly damaged, and by the retina breaking away from its mesh of blood vessels that nourish it (retinal detachment).

While each disease has its own specific effect on the retina, a general scenario for many of the retinopathies is as follows:

• Blood flow to the retina is disrupted, either by blockage or breakdown of the various vessels.  This can lead to bleeding (hemorrhage) and fluids, cells, and proteins leaking into the area (exudates).
• There can be a lack of oxygen to surrounding tissues (hypoxia) or decreased blood flow (ischemia).
• Chemicals produced by the body then can cause new blood vessels to grow (neovascularization), however, these new vessels generally leak and cause more problems.  Neovascularization can even grow on the colored part of the eye (iris).  The retina can swell and vision will be affected.

Incidence; Causes and Development

Diabetic retinopathy is the leading cause of blindness in people ages 20 to 74.  In the United States, new cases of blindness are most often caused by diabetic retinopathy.  Among these new cases of blindness, 12% are people between the ages of 20 to 44 years, and 19% are people between the ages of 45 to 64 years.

Retinopathy (damage to the retina) has various causes, but it is usually caused by diabetes.  A hardening or thickening of the retinal arteries is called arteriosclerotic retinopathy.  High blood pressure in the arteries of the body can damage the retinal arteries and this is called hypertensive retinopathy.  The spreading of a syphilis infection to the retinal blood vessels causes syphilitic retinopathy, and diabetes damages the retinal vessels resulting in a condition called diabetic retinopathy.  Sickle cell anemia also affects the blood vessels in the eyes.  Exposure to the sun (or looking at the sun during an eclipse) can cause damage (solar retinopathy), as well as certain drugs (for example, chloroquine, thioridazine, and large doses of tamoxifen).  The arteries and veins can become blocked, thus resulting in a retinal artery or vein occlusion.  These are just some of the causes of the various retinopathies.

In the case of Diabetic Retinopathy, as the diabetes progresses, the blood vessels that feed the retina become damaged in different ways.  The damaged vessels can have bulges in their walls (aneurysms), they can leak blood into the surrounding jelly-like material (vitreous) that fills the inside of the eyeball, they can become completely closed, or new vessels can begin to grow where there would not normally be any: although these new blood vessels are growing in the eye, they cannot nourish the retina and they bleed easily, releasing blood into the inner region of the eyeball, which can cause dark spots and cloudy vision.

Retinal Vein Occlusion generally occurs in the elderly.  There is usually a history of other systemic disease, such as diabetes or high blood pressure.  The central retinal vein, or the retinal veins branching off of it, can become compressed, thus stopping the drainage of blood from the retina.  This may occur if the central retinal artery hardens.

Retinal Artery Occlusion is generally the result of an embolism that dislodges from somewhere else in the body and travels to the eye.

Looking directly at the sun or watching an eclipse can cause damage known as Solar Retinopathy.

Drug-related Retinopathies
Certain medications can affect different areas of the retina.  For example, doses of 20-40mg per day of tamoxifen usually does not cause a problem, but much higher doses may cause irreversible damage.

Patients taking chloroquine for lupus, rheumatoid arthritis, or other disorders may notice a decrease in vision.  If so, discontinuing medication will stop, but not reverse, any damage.  However, patients should never discontinue medication without the advise of their physician.

Patients taking thioridazine may notice a decrease in vision or color vision.

These drug-related retinopathies generally only affect patients taking large doses.  However, patients need to be aware if any medication they are taking will affect the eyes.  Patients need to inform their doctors of any visual effects.

Signs and Symptoms

Retinopathy is a "silent" disease of the back of the eye – it has no symptoms during its early stage.  A person with retinopathy could have it for years with no pain or other symptoms until the condition progresses enough to cause vision loss.

Diabetic Retinopathy begins prior to any outward signs of disease being noticed.  Once symptoms are noticed, they include poorer than normal vision, fluctuating or distorted vision, cloudy vision, dark spots, episodes of temporary blindness, or permanent blindness.

Non-proliferative Diabetic Retinopathy is characterized by leakage from small retinal blood vessels (capillaries).  This leakage permits protein to accumulate in the retina causing the retina to become swollen or "waterlogged" .  If this swelling occurs in the macula (area of central vision), sight may be significantly diminished.  Retinal capillaries may also become closed off resulting in poor retinal nutrition.  Loss of circulation to the macula can result in severe loss of central vision.

Proliferative Diabetic Retinopathy occurs when widespread impairment of retinal nutrition results from capillary leakage and closure.  The poorly nourished retina then sends out some type of chemical distress signal that causes new blood vessels to bud and grow (proliferate) on the retinal surface.  Unfortunately these new blood vessels are very fragile and usually rupture, permitting bleeding to occur within the eye.  Scar tissue may grow around the abnormal blood vessels and lead to pulling on the retina, causing retinal detachment and possible permanent blindness.  The proliferative form of diabetic retinopathy is present in approximately 20% of patients with diabetes of ten years' duration.

Symptoms of Retinal Vein Occlusion include a sudden, painless loss of vision or field of vision in one eye.  There may be a sudden onset of floating spots (floaters) or flashing lights.  Vision may be unchanged or decrease dramatically.

Transient loss of vision may precede Retinal Artery Occlusion.  Symptoms of a central retinal artery or branch occlusion include a sudden, painless loss of vision or decrease in visual field.  Some 10% of the cases of a retinal artery occlusion occur because of giant cell arteritis (a chronic vascular disease).

In cases of Solar Retinopathy, there may be a loss of the central visual field or decreased vision.  The symptoms can occur hours to days after the incident.

Diagnosis and Tests

The damaged retinal blood vessels and other retinal changes are visible to an eye doctor when an examination of the retina (fundus exam) is performed.  This can be done using a hand-held instrument called an ophthalmoscope or another instrument called a binocular indirect ophthalmoscope, allowing the doctor to see the back of the eye.  Certain retinopathies have classic signs (for example, vascular "sea fans" in sickle cell, dot and blot hemorrhages in diabetes, flame-shaped hemorrhages in high blood pressure).  Patients may then be referred for other tests to confirm the underlying cause of the retinopathy.  These tests include blood tests and measurement of blood pressure.

Fluorescein angiography, where a dye is injected into the patient and the back of the eyes are viewed and photographed, helps to locate leaky vessels.

Treatment and Prevention

For diabetics, maintaining proper blood sugar and blood pressure levels is very important, but some form of retinopathy will usually occur, given enough time.

Patients with Retinal Artery Occlusion should be referred to a cardiologist.  Patients with retinal vein occlusion need to be referred to a physician, as they may have an underlying systemic disorder, such as high blood pressure.

The best form of prevention is regular eye examinations that detect early signs of retinopathy.  Patients on certain medications should have more frequent eye exams.  They also should have a baseline eye exam when starting the drug.

Proper medical treatment for any of the systemic diseases known to cause retinal damage will help prevent retinopathy.

Prognosis

Nonproliferative retinopathy has a better prognosis than proliferative retinopathy.  Prognosis depends upon the extent of the retinopathy, the cause, and promptness of treatment.