CHAPTER 228

Retinal Disorders

The cornea and lens focus light onto the retina, the transparent, light-sensitive membrane on the inner surface of the back of the eye. The central area of the retina, called the macula, contains a high density of color-sensitive photoreceptor (light-sensing) cells. These cells, called cones, produce the sharpest visual images and are responsible for central and color vision. The peripheral area of the retina, which surrounds the macula, contains photoreceptor cells called rods, which respond to lower light levels but are not color sensitive. The rods are responsible for peripheral vision and night vision.

The optic nerve carries signals generated by the photoreceptors (cones and rods). Each photoreceptor is joined to the optic nerve by a tiny nerve branch. The optic nerve is connected to nerve cells that carry signals to the vision center of the brain, where they are interpreted as visual images.

Viewing the Retina

The optic nerve and the retina have a rich supply of blood vessels that carry blood and oxygen. Part of this supply of blood vessels comes from the choroid, which is the layer of blood vessels that lies between the retina and the outer white coat of the eye (the sclera). The central retinal artery (the other major source of blood to the retina) reaches the retina near the optic nerve and then branches out within the retina. Blood drains from the retina into branches of the central retinal vein. The central retinal vein exits the eye near the optic nerve.

When examining a person’s retina, a doctor puts drops in the eye to dilate the pupil. This allows the retina to be seen in much more detail with an ophthalmoscope.

Retinal disorders are often diagnosed and treated by an ophthalmologist (a medical doctor who specializes in diagnosing and treating eye diseases and performing eye surgery). Frequently, treatment is by an ophthalmologist who specializes in disorders of the retina.

Age-Related Macular Degeneration

Age-related macular degeneration (also called age-related maculopathy) causes progressive damage to the macula, the central and most vital area of the retina, resulting in gradual loss of central vision.

Central vision becomes washed out and loses detail, and straight lines may appear wavy.

Changes in the eye that characterize the disorder can usually be seen by a doctor using a hand-held ophthalmoscope.

Dietary supplements may help slow progression of the disorder.

Eye injections and laser treatments may be necessary for some people.

Age-related macular degeneration is the most common cause of irreversible loss of central vision in the elderly. It is equally common among men and women.

Causes

The following are risk factors for the disorder:

Older age

Smoking

Fair skin

Certain genetic abnormalities

High blood pressure

A diet low in omega-3 fatty acids (for example, in certain fish) and dark green leafy vegetables

Types: There are two forms of age-related macular degeneration:

Dry (atrophic)

Wet (neovascular or exudative)

Ninety percent of people with macular degeneration have the dry type. However, 90% of the blindness caused by macular degeneration occurs in the 10% of people who have the wet form.

In dry macular degeneration, the tissues of the macula thin as cells disappear. Both eyes may be affected simultaneously in the dry form. There is no evidence of scarring or of bleeding or other fluid leakage in the macula.

Wet macular degeneration starts off as the dry type. In wet macular degeneration, abnormal blood vessels develop under the macula. These vessels may leak fluid and blood under the retina (hence the description as “wet”). Eventually, a mound of scar tissue develops under the retina. The wet form develops in one eye first but eventually may affect both eyes.

Symptoms

In dry macular degeneration, central vision slowly and painlessly worsens. Objects may appear washed out, or fine detail may be lost.

In wet macular degeneration, loss of vision tends to progress quickly and may be sudden if one of the abnormal blood vessels bleeds. The first symptom may be distortion of vision in one eye, so that fine, straight lines appear wavy. Often, difficulty with reading or watching television results.

Age-related macular degeneration can severely damage vision, but it usually does not lead to complete blindness. Vision at the outer edges of the visual field (peripheral vision) is generally not affected. The dry type tends to cause slower vision loss.

Diagnosis

Doctors can usually diagnose macular degeneration by examining the eyes with an ophthalmoscope or a slit lamp. The retinal damage is almost always visible even before symptoms develop. Sometimes fluorescein angiography—a procedure in which a doctor injects dye into a vein and photographs the retina—is used to confirm the diagnosis. Optical coherence tomography, an imaging study, can sometimes help in making the diagnosis.

Treatment

No treatment is currently available to undo damage caused by the dry type. No treatment is currently recommended for mild disease.

Dietary Supplements: People with moderate to severe dry macular degeneration and those who have wet macular degeneration in one eye benefit from high doses of antioxidants (vitamin C, vitamin E, and beta-carotene [a form of vitamin A]) and zinc, with a small amount of copper. People who have used tobacco products within the past seven years should not take beta-carotene or vitamin A because these supplements can increase the risk of developing lung cancer. Controlling high blood pressure and eating more omega-3 fatty acids and dark green leafy vegetables may help slow progression of the disorder.

Drug Treatments and Laser Procedures: In the wet type of macular degeneration, drugs such as ranibizumab, bevacizumab, or pegaptanib can be injected into the eye to cause the new blood vessels to stop leaking. These injections need to be repeated every 1 to 2 months, but the injections can improve vision in some people, and one in three people regains reading vision. Another treatment is photodynamic therapy. In this treatment, a substance that sensitizes the retinal blood vessels to laser light is injected into a vein in the arm, and then a beam of laser light is used to destroy the abnormal new blood vessels. If the new blood vessels are not directly under the macula, a thermal laser can be used to destroy them before they do further harm. Corticosteroid drugs can sometimes be injected into the eye. Surgery is done only if these other treatments are not working.

Adjusting to Vision Loss: Magnifiers, reading glasses, telescopes, and closed-circuit television magnifying devices may help people with poor vision. Computer users can select from a variety of low-vision aids (see box on page 1426). For example, one device projects an enhanced image from the computer onto an undamaged part of the retina. Certain types of software display computer data in large print or read the data aloud in a synthetic voice. Counseling regarding the types of services that are available for people with poor vision is advisable and is typically given by a low-vision specialist (an ophthalmologist or optometrist who specializes in treating people with very poor vision).

Epiretinal Membrane

Epiretinal membrane (also called cellophane maculopathy, macular pucker, or premacular fibrosis) is formation of a thin membrane over the retina, which interferes with vision.

Epiretinal membrane is a thin membrane of scar tissue that forms over the retina and contracts, wrinkling the retina underneath. Epiretinal membrane typically occurs after age 50 and is most common among people older than 75.

With aging, the vitreous humor (the jellylike substance inside the back part of the eye; also called the vitreous) shrinks. Various conditions that can cause or contribute to wrinkling of the retina include the following:

Diabetic retinopathy

Uveitis

Retinal detachment

Injury to the eye

Most of the time, however, no clear cause can be identified.

Symptoms may include blurred vision or distorted vision (for example, straight lines may appear wavy). Many people say that it seems like they are looking through plastic wrap or cellophane. Doctors confirm the diagnosis by looking at the back of the eye with an ophthalmoscope. Fluorescein angiography and optical coherence tomography may also be helpful.

Most people need no treatment. If vision is poor, the membrane can be removed surgically, using a procedure called a membrane peel. This procedure can be done under local anesthesia in an operating room and usually takes about 30 minutes.

Detachment of the Retina

Retinal detachment is separation of the retina from the underlying layer to which it is attached.

People notice a sudden increase in floaters, a sudden onset of flashing lights, a curtain or veil across vision, or sudden loss of vision.

Doctors make the diagnosis by looking in the eye with an ophthalmoscope.

Most retinal detachments can be repaired, resulting in improved vision if done soon after the detachment occurs.

A retinal detachment may begin in a small area, usually as the result of a retinal tear. If the small area is not soon reattached, the entire retina can detach. Retinal tears that can lead to retinal detachment are more likely to occur in people who have or have had the following:

Severe nearsightedness (myopia)

Cataract surgery

An eye injury

When the retina detaches, it separates from part of its blood supply. Unless the retina is reattached, it may be permanently damaged by lack of blood. Fluid or blood from a damaged blood vessel may also collect between the retina and the underlying tissue, further worsening vision.

Symptoms and Diagnosis

A retinal detachment is painless. People usually see an increase in small, floating objects (floaters) or many flashes of bright light that last less than a second. Peripheral vision is typically lost first, and vision loss spreads as the detachment progresses. The loss of vision resembles a curtain or veil falling across the line of sight. If the macula becomes detached, vision rapidly deteriorates, and everything becomes blurred.

After applying eye drops to dilate the pupil, doctors examine the retina using an ophthalmoscope and can usually see a detachment. If the detachment is not visible, an ultrasound of the eye can reveal it.

Prognosis

Vision usually improves, except in the following conditions:

The retina has been detached for several days or weeks.

Bleeding or scarring has occurred.

The macula has been detached or is damaged.

Treatment

Most retinal detachments can be repaired. The surgeon seals the tears with laser surgery or freezing therapy (cryopexy). Then the surgeon draws the retina and the eye wall together either by placing a band around the eye (a scleral buckle) or by removing the vitreous jelly behind the lens and in front of the retina with surgery called a vitrectomy. A gas bubble is often used to hold the retina is place.

Retinitis Pigmentosa

Retinitis pigmentosa is a rare, progressive degeneration of the retina that eventually causes moderate to severe vision loss.

Retinitis pigmentosa is often inherited. One form has a dominant pattern of inheritance, requiring only one abnormal gene from either parent. Other forms are recessive and require an abnormal gene from both parents. An X-linked recessive form occurs mainly in males who inherit one abnormal gene from their mother. In some people, mostly males, hearing loss may also be inherited (a disorder called Usher’s syndrome).

The photoreceptors (light-sensing cells) of the retina that are responsible for vision when light is low (rods) gradually degenerate, so that vision becomes poor in the dark. The first symptoms often begin in early childhood. Over time, peripheral vision progressively deteriorates. In the late stages of the disease, the person typically has only a small area of central vision and possibly some peripheral vision remaining (tunnel vision).

When examining the retina with an ophthalmoscope, doctors see specific changes that suggest the diagnosis. Tests such as the electroretinogram, which evaluates the electrical response of the retina to light, may help to confirm the diagnosis.

Family members should be examined so that the inheritance pattern can be determined if possible. If the disorder is present in other family members, genetic counseling should be considered before having children.

No conventional treatment can reverse retinal damage. Vitamin A is recommended by some doctors in an attempt to slow the progression of the disorder. Gene therapy and implantable cells that make a compound to nourish the retina are under investigation.

Blockage of Central Retinal Arteries and Veins

A blood vessel in the retina may become blocked, causing sudden, painless loss of vision.

Doctors typically make the diagnosis by looking in the eye with an ophthalmoscope and sometimes by performing tests.

Treatment often is unsuccessful.

Blockage may occur in the main artery or vein in the retina (arteries supply blood, and veins drain blood away) or in their branches.

The central retinal artery, the main vessel that supplies blood to the retina, can become completely blocked by a particle, such as a piece of atherosclerotic plaque (see art on page 397) or a blood clot, that floats in the bloodstream (embolus) until it gets stuck in and blocks a vessel. Giant cell arteritis, an inflammation of the blood vessels, is also a possible cause of retinal artery blockage.

Retinal veins may become blocked in people with glaucoma, diabetes, or high blood pressure. Such blockage occurs mainly in older people.

Symptoms

If the central retinal artery is blocked, the affected eye has a sudden but painless loss of vision over the entire field of vision or sometimes only a part of it. Vision loss ranges from mild to severe.

Blockage of the central retinal vein causes similar symptoms except that vision loss sometimes is gradual, occurring over days or weeks. Recurrences are common.

Blockage of the central retinal artery or vein may also cause growth of abnormal blood vessels on the retina or iris. Sometimes these abnormal blood vessels bleed or cause glaucoma.

Diagnosis

Using an ophthalmoscope, doctors can see changes in blood vessels and the retina. If the central retinal artery is blocked, the retina may be pale. If the central retinal vein is blocked, the veins may be engorged or enlarged, and the front of the optic nerve may be swollen.

Fluorescein angiography—a procedure in which a doctor injects dye into a vein and then photographs the retina—helps determine the extent of damage to the retina and helps the doctor plan treatment. Doppler ultrasound scanning may sometimes be used to observe blood flow in the vessels.

If the artery has been blocked by an embolus, doctors need to search for a source. They often do tests such as echocardiography or carotid artery ultrasonography.

Treatment

Treatments for blockage of the main artery or vein or their branches tend not to be very effective. Preventing such blockages by controlling risk factors (for example, high blood pressure, diabetes, and other risk factors for atherosclerosis) is more effective.

Blockage of an Artery: Immediate treatment is often given in an attempt to unblock the retinal artery. However, treatments are rarely effective. Pressure inside the eye sometimes can be lowered by intermittently massaging the closed eyelids with the fingers. Alternatively, a procedure called anterior chamber paracentesis may help lower pressure inside the eye. In this procedure, drops are placed in the eye to numb the eye, and then a needle is inserted into the anterior chamber to withdraw a small amount of fluid, thereby rapidly lowering the pressure in the eye. Lowering the pressure inside the eye by massage or by anterior chamber paracentesis may dislodge a blood clot or other embolus and allow it to enter a smaller branch of the vessel, thereby reducing the area of damage to the retina.

Vein Blockage of a Vein: Laser treatment of the leaking blood vessels can help improve vision for people with a blockage in a branch of the retinal vein. Injections of drugs into the eye are being investigated as treatments for vein blockage.

Abnormal Blood Vessel Growth: Laser treatment may be used to destroy abnormal blood vessels if they develop on the iris or angle.

Hypertensive Retinopathy

Hypertensive retinopathy is damage to the retina caused by high blood pressure.

When blood pressure becomes high (hypertension—see page 333), the retina may become damaged. Hypertension damages the small blood vessels in the retina, causing their walls to thicken, which decreases the amount of blood that can flow through them. As a result, the blood supply to the retina is reduced. Patches of the retina may become damaged because the blood supply is inadequate. As hypertensive retinopathy progresses, blood may leak into the retina. These changes lead to a gradual loss of vision, particularly if they affect the macula, the central part of the retina. Even mild hypertension may damage the retinal blood vessels if it goes untreated for years.

Using an ophthalmoscope, doctors can observe the typical appearance of the retina in people with high blood pressure. The amount of damage to the retinal blood vessels tends to correlate with the amount of damage to blood vessels in other organs affected by hypertension, such as the brain, heart, and kidneys. When blood pressure is extremely high, doctors may be able to see other changes in the eye, such as swelling of the front of the optic nerve.

Did You Know…

By looking into the eye with an ophthalmoscope, doctors can see the eye’s arteries and veins. The appearance of these blood vessels can tell doctors how hypertension and atherosclerosis have affected other blood vessels in the body.

The goal of treatment is to lower blood pressure. When high blood pressure is severe and life threatening, treatment may be needed immediately to save vision and avoid other complications, including stroke, heart failure, kidney failure, and heart attack.

Diabetic Retinopathy

Diabetic retinopathy is damage to the retina as a result of diabetes.

Blood vessels in the retina can leak.

New blood vessels may develop, sometimes leading to bleeding (hemorrhage), scar formation, or retinal detachment.

The diagnosis is based on an eye examination after the pupil is dilated with eye drops.

Controlling blood sugar and blood pressure are important for people who have diabetic retinopathy or who are at risk of developing it.

Laser treatments can sometimes prevent or delay further damage.

Diabetes mellitus is among the leading causes of blindness in the United States and other developed countries. Some retinal change occurs in virtually all people with diabetes, whether or not they use insulin therapy. People with diabetes who also have high blood pressure are at much higher risk of developing diabetic retinopathy because both conditions tend to damage the retina. Pregnancy can cause diabetic retinopathy to worsen.

High levels of sugar (glucose) in the blood make the walls of small blood vessels, including those in the retina, weaker and, therefore, more prone to damage. Damaged retinal blood vessels leak blood and fluid into the retina.

The extent of retinopathy and vision loss is related mostly to the following:

How well blood sugar levels are controlled

How well blood pressure is controlled

How long the person has had diabetes

In general, retinopathy appears 5 years after people develop type 1 diabetes. Because diagnosis of type 2 diabetes may not occur for years, retinopathy may be present by the time people receive the diagnosis of type 2 diabetes.

Symptoms

Diabetes mellitus can cause two types of changes in the eye.

In nonproliferative retinopathy, small blood vessels in the retina leak fluid or blood and may develop small bulges. Areas of the retina affected by leakage may swell, causing damage to parts of the field of vision. At first, the effects on vision may be minimal, but gradually vision may become impaired. Blind spots may occur, although these may not be noticed by the person and are usually discovered only if testing is done. If leakage occurs near the macula, central vision may blur. Swelling of the macula (macular edema) due to leakage of fluid from blood vessels can eventually cause significant loss of vision.

In proliferative retinopathy, damage to the retina stimulates the growth of new blood vessels. The new blood vessels grow abnormally, sometimes leading to hemorrhage or scarring. Extensive scarring may cause retinal detachment. Proliferative retinopathy tends to result in greater loss of vision than does nonproliferative retinopathy. It can result in total or near-total blindness due to a large hemorrhage into the vitreous humor (the jellylike substance inside the back part of the eye) or to a type of retinal detachment called traction retinal detachment. Growth of new blood vessels can also lead to glaucoma. Macular edema with significant loss of vision can occur with proliferative diabetic retinopathy as well.

Diagnosis

Doctors diagnose nonproliferative and proliferative retinopathy by examining the retina with an ophthalmoscope or a slit lamp. Fluorescein angiography (see page 1424) helps to determine the location of the leakage, as well as areas of poor blood flow and the areas of new abnormal blood vessel formation.

Prevention

The best way to prevent diabetic retinopathy is to control diabetes and keep blood pressure at normal levels. People with diabetes should have an annual eye examination, in which the pupil is dilated with eye drops, so that retinopathy can be detected and any necessary treatment can be started early. Pregnant women with diabetes should have these eye examinations about once every 3 months.

Treatment

Treatment consists of laser photocoagulation, in which a laser beam is aimed into the eye at the retina to slow the growth of abnormal new retinal blood vessels and decrease leakage. Laser photocoagulation may need to be repeated. If bleeding from damaged vessels has been extensive, a procedure called vitrectomy may be needed. In this procedure, blood is removed from the cavity in which the vitreous humor lies. Vision often improves after vitrectomy for vitreous hemorrhage, and vision may improve after vitrectomy for traction retinal detachment. Laser treatment only rarely improves vision, but it commonly prevents further deterioration. Newer treatments that are being investigated involve injecting drugs into the eye. These treatments may help improve vision for some people with severe vision loss.

Endophthalmitis

Endophthalmitis is infection inside the eye.

Eye surgery, eye injury, or infection in the bloodstream can cause the infection.

Severe eye pain, eye redness, and loss of vision may occur.

Cultures are taken of eye fluids, and antibiotics are given as soon as possible.

Endophthalmitis is uncommon. It is caused by organisms that have entered the eye through a surgical incision or an injury to the eyeball or, less often, have traveled through the bloodstream into the eye. Infection in the bloodstream has many possible causes, such as intravenous drug use, an abscess (a collection of pus), skin ulcers, infections such as pneumonia or sepsis, or surgery anywhere in the body. Infection is usually due to bacteria, but fungi or protozoa may also be responsible. Viruses can also cause extensive eye infections, but these are not usually classified as endophthalmitis.

Symptoms may be severe and include pain, redness in the white of the eye, extreme sensitivity to bright light, and partial or complete loss of vision. The diagnosis is based on the symptoms, an examination of the eye, cultures, and sometimes antibody or DNA testing. Cultures may be taken from the aqueous humor (fluid inside the front of the eye, also called the aqueous) and the vitreous humor (the jellylike substance inside the back part of the eye) to determine which organisms are responsible and which drugs are most active against them.

Endophthalmitis is a medical emergency. Immediate treatment with antibiotics is usually needed to preserve vision. A delay of even a few hours can result in irreversible vision loss in extreme cases. The choice of antibiotic may be adjusted depending on which organism is found to be causing the endophthalmitis. Antibiotics may be injected into the eye and given intravenously or orally. Oral corticosteroids may also be given for a few days after injection of antibiotics into the eye. Surgery may be needed to remove infected tissue from inside the eye, which may improve the chances of stopping the infection.

Cancers Affecting the Retina

Cancers affecting the retina usually occur in the choroid, a dense layer of blood vessels that supplies the retina. The choroid is sandwiched between the retina and the sclera (the outer white part of the eye). Because the retina depends on the choroid for its support and half of its blood supply, damage to the choroid by a cancer is likely to affect vision.

Choroidal Melanoma: Choroidal melanoma is a cancer that originates in the pigment-producing cells (melanocytes) of the choroid. Choroidal melanoma is the most common cancer originating in the eye. It is most common among people with fair complexions and blue eyes. In its early stages, the cancer usually does not interfere with vision. Later, it may cause blurred vision or retinal detachment, with symptoms such as flashes of light, a veil or curtain across the visual field, or a sudden increase or change in floaters. Melanomas, particularly if large, may extend into the orbit or spread through the bloodstream (metastasize) to other parts of the body and may be fatal.

Early diagnosis is important because smaller tumors are easier to cure. The diagnosis is made using an ophthalmoscope and performing tests, which may include ultrasound scanning, computed tomography (CT), and serial photographs.

If the melanoma is small, treatment with a laser, radiation, or an implant of radioactive materials may preserve vision and save the eye. If the cancer is large, the eye may have to be removed.

Choroidal Metastases: Choroidal metastases are cancers that have spread to the choroid from other parts of the body. Because of its rich blood supply, the choroid is often a place to which cancers from other parts of the body may spread. In women, breast cancer is the most common cause. In men, cancers of the lung or prostate are the most common causes.

Often, these cancers cause no symptoms until they are advanced. Symptoms, when they develop, are often loss of vision or symptoms of retinal detachment. Vision loss may be severe.

The diagnosis is sometimes made during a routine eye examination with an ophthalmoscope. The diagnosis is aided by ultrasound scanning. Confirmation of the diagnosis may involve using a fine needle to remove a sample of tissue for examination under a microscope (biopsy). Treatment is usually with chemotherapy and radiation therapy.