Retinopathies
Retinopathy is a noninflammatory disease of the retina, the thin membrane that lines the back of the eye and contains light-sensitive cells (photoreceptors). Light enters the eye and is focused onto the retina. The photoreceptors send a message to the brain via the optic nerve and the brain then "interprets" the electrical message sent to it, resulting in vision. The macula is a specific area of the retina responsible for central vision and the fovea is an tiny area about 1.5 mm located in the macula responsible for sharp vision. When looking at an object, the fovea should be directed right at it. Damage to the retina causes vision deficits and even blindness.
Retinopathy, or damage to the retina, has various causes. While each cause has its own specific effect on the retina, a general scenario for many of the retinopathies is as follows (note: not all retinopathies necessarily affect the blood vessels). 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 bea lack of oxygen to surrounding tissues (hypoxia), or decreased blood flow (ischemia). Chemicals produced by the body then can cause new blood vessels togrow (neovascularization); however, these new vessels generally leak, cause the retina to swell, and vision will be affected.
Retinopathies are divided into two broad categories, simple--or nonproliferative retinopathies, and proliferative retinopathies. Thesimple retinopathies include the defects identified by bulging of the vesselwalls, by bleeding into the eye, by small clumps of dead retinal cells calledcotton wool exudates, and by closed vessels. This form of retinopathy is considered mild. The proliferative, or severe, forms include the defects causedby 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).
There are many causes of retinopathy, and some of the more common ones are listed below.
Diabetic retinopathy--caused by diabetes mellitus--is the leading cause of blindness in people ages 20-74. Diabetes is a complex disorder characterized byan inability of the body to properly regulate the levels of sugar and insulin (a hormone made by the pancreas) in the blood. As diabetes progresses, theblood vessels that feed the retina become damaged in different ways. They canhave bulges in their walls (aneurysms), they can leak blood into the jelly-like fluid that fills the eyeball (vitreous), they can become completely closed, or new vessels can begin to grow where there would not normally be blood vessels. However, these new blood vessels cannot nourish the retina and they bleed easily, releasing blood into the inner region of the eyeball, which cancause dark spots and cloudy vision. Diabetic retinopathy begins prior to anyoutward signs of the disease. Once symptoms are noticed, they include poorerthan normal vision, fluctuating or distorted vision, cloudy vision, dark spots, episodes of temporary blindness, or permanent blindness. Diabetic retinopathy will occur in 90% of persons with type 1 diabetes (insulin-dependent, orinsulin requiring) and 65% of persons with type 2 diabetes (non-insulin-dependent, or not requiring insulin) within about 10 years of diabetes onset. 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 20-44 years, and 19% are people between the ages of 45-64 years.
Hypertensive retinopathy is caused by hypertension (high blood pressure). Some blood vessels can narrow, others can thicken and harden (arteriosclerosis).There will be flame-shaped hemorrhages and macular swelling (edema). This edema may cause distorted or decreased vision.
Sickle-cell anemia also affects blood vessels in the eye. This disease occursmostly in American-African populations and is a hereditary disease that affects the red blood cells. The sickle-shaped blood cell reduces blood flow, which also includes blood flow in the retina. Vision problems will not appear early on in the disease; however, patients need to be followed closely in caseneovascularization occurs.
Retinal vein occlusion generally occurs in the elderly. There is usually a history of other systemic disease, such as diabetes or high blood pressure. Thecentral retinal vein (CRV), or the retinal veins branching off of the CRV, can become compressed, stopping the drainage of blood from the retina. This may occur if the central retinal artery hardens. Symptoms 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; or vision may decrease dramatically.
Retinal artery occlusion is generally the result of an embolism (blood clot)that dislodges from somewhere else in the body and travels to the eye. Temporary loss of vision may precede an occlusion. Symptoms include a sudden, painless loss of vision or decrease in visual field. Ten percent of the cases of aretinal artery occlusion occur because of giant cell arteritis (a chronic vascular disease).
Solar retinopathy can be caused by looking directly at the sun, as when watching an eclipse. This can cause loss of the central visual field or decreasedvision. The symptoms can occur hours or days after the incident.
Certain medications can affect different areas of the retina. Doses of 20-40mg a day of tamoxifen usually does not cause a problem, but much higher dosesmay 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 informed if medications will affect their eyes, and they also need to inform their doctors of any visual effects from medications.
Damaged retinal blood vessels and other retinal changes are visible to an eyedoctor during an examination of the retina. This can be done using a hand-held instrument called an ophthalmoscope, or another instrument called a binocular indirect ophthalmoscope, that allow 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. Also, fluorescein angiography, where adye is injected into the patient and the back of the eyes are viewed and photographed, helps to locate leaky vessels.
Treatment for retinopathy usually begins with an ophthalmologist, a physicianwho specialize in eye disorders. Because retinopathy can result from underlying systemic causes, a general physician should be consulted as well. For drug-related retinopathies, the treatment is generally discontinuation of the drug (only under the care of a physician).
In some cases, laser surgery can help to prevent blindness or lessen vision loss. The high-energy light from a laser is aimed at the weakened blood vessels in the eye, destroying them. Scars will remain where the laser treatment was performed. For that reason, laser treatment cannot be performed in all sections of the retina. For example, laser photocoagulation at the fovea would destroy the area for sharp vision. Panretinal photocoagulation may be performedin which a larger area is treated at the periphery (edges) of the retina aimed at decreasing neovascularization. Prompt treatment of proliferative retinopathy may reduce the risk of severe vision loss by 50%. Patients with retinalartery occlusion should be referred to a cardiologist. Patients with retinalvein occlusion need to be referred to a physician, as they may have an underlying systemic disorder such as high blood pressure. Nonproliferative retinopathy has a better prognosis (expected outcome) than proliferative retinopathy. Prognosis depends upon the extent of the retinopathy, the cause, and promptness of treatment.
To help reduce the risk of retinopathy, complete eye examinations done regularly can help to detect early signs. Patients on certain medications should have more frequent eye exams, as well as a baseline eye exam when starting thedrug. Persons with diabetes must take extra care to have thorough, periodic eye exams, especially if early signs of visual impairment are noticed. Anyoneexperiencing a sudden loss of vision, decrease in vision or visual field, flashes of light, or floating spots, should contact their eye doctor immediately.
Proper medical treatment for any of the systemic diseases known to cause retinal damage will help prevent retinopathy. For diabetics, maintaining proper blood sugar and blood pressure levels is important; however, some form of retinopathy will usually occur in diabetics, given enough time. A proper diet, particularly for those persons with diabetes, and stopping smoking, will also help delay retinopathy.
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