Read an Excerpt
CHAPTER 1: What is ARMD?
Macular degeneration is one of the biggest secrets in the world.
--Emil F. Hubka, Jr., ARMD patient
This has become a true epidemic of our time.
--Jerry Chader, Ph.D., Chief Scientific Officer, The Foundation Fighting Blindness
"I thought I needed new glasses," Zelda Grant remembers. "I was shocked to discover that I have age-related macular degeneration. 'Macular what?' I said to my doctor. I had never heard of it before, and I could hardly believe that some disease I had never heard of was stealing my eyesight." Alarmingly, Zelda's experience is very common. Age-Related Macular Degeneration, or ARMD, is the leading cause of adult vision loss in the United States. It affects more people than all of the better known eye diseases combined: glaucoma, cataracts, and diabetic retinopathy. According to the respected Beaver Dam Eye Study--the most comprehensive attempt to estimate the demographics of macular degeneration in the United States--18 percent of seniors aged sixty-five to seventy-four and nearly 30 percent of seniors over seventy-five show early evidence of the condition. One out of every twenty-five Americans over sixty-five, or 1,367,000 people, suffers significant vision loss from advanced macular degeneration. Clearly, if y
ou have ARMD you are not alone.
What is Age-Related Macular Degeneration?
Macular degeneration dismantles central vision painlessly and silently, leaving peripheral vision intact. As a result, people with advanced macular degeneration do not feel any change in their eyes, and they do not appear any different to their friends and family, but their experience of the world and of their own capacities changes radically. Because macular degeneration leaves peripheral vision intact, people with ARMD can see whatever rests at the edges of their vision, but cannot see clearly whatever they look at directly. They find it difficult to recognize their grand-children's photographs, for example, but can describe the check pattern of a black and white tile floor. They cannot read a bus sign, but can see a leaf on the sidewalk out of the corners of their eyes. This combination of visual ability and vision loss is enormously frustrating, not the least because it takes away what we most want to see, leaving visible what appears to be irrelevant. As Carolyn See, an English professor, remarks dryly i
n her candid memoir of living with macular degeneration, "It begins in the center of your vision and after a while you can't read or drive or recognize your relatives. They say you'll always be able to pick up a thread on the carpet. But even with full vision, picking up threads on the carpet wasn't high on my list of activities."
Why Has Macular Degeneration Been a Big Secret?
Macular degeneration is coming out of the closet. Three years ago, patients came to appointments asking me to check their eyes for signs of glaucoma. Today they arrive asking about macular degeneration. But macular degeneration has been a leading cause of vision loss in seniors for decades. Why did it take us until the late 1990s to talk about it? No one is quite sure.
The first explanation may lie in the physiology of ARMD. Even though macular degeneration was first named by a German scientist in 1885, the technology used to understand it in detail was not developed until the 1960s. Unlike cataracts, which can easily be seen, or glaucoma, which can easily be measured, macular degeneration is more difficult to analyze and to treat. Ophthalmologists have tended to focus their energies on developing fine new surgeries that have helped improve the sight of hundreds of thousands of people with many different eye conditions. But macular degeneration never looked like a condition that would respond readily to surgery, so it wound up a bit lower on the research priority list.
A second explanation of why ARMD has not been talked about may lie in the category of people affected by it: seniors. Until about ten years ago, ARMD was called senile macular degeneration, which may be another clue to its anonymity. Although senile is a word we commonly associate with declining mental health, senile macular degeneration simply means macular degeneration in older people. But no matter how you define it, senile still connotes decline, and for much of this century declining vision was simply accepted as the result of "just growing old." But seniors like Zelda and Carolyn are now living longer and in better health than their parents and grandparents. Healthy longevity is on the rise: a sixty-five-year-old may have twenty to forty more years of reading, entertaining, traveling, and sports ahead of her; she may not even feel ready to retire. Seniors today are also less willing to accept adversity from aging as quietly as their parents and grandparents did. Zelda and her peers want to know, justifi
ably, why there is so little attention paid to macular degeneration, why their insurance companies don't cover visual aids or therapy for low vision, and when a cure will be developed. Vision loss is no longer an expected part of just growing old, nor should it be.
Macular Degeneration Gains Attention
Macular degeneration has become a major health issue, and more and more physicians, pharmaceutical companies, and laboratories are searching for cures and for a clearer understanding of what causes ARMD. But even with this new attention, the total amount of research dollars devoted to ARMD is still small considering that it is the biggest cause of irreversible vision loss in the country:more than cataracts, glaucoma, and diabetic retinopathy combined. The National Eye Institute (NEI), a division of the National Institutes of Health, has ranked ARMD its number one priority, but for the magnitude of the problem a relatively small percentage of the national health budget is devoted specifically to ARMD research. Unless we speak up, this situation is unlikely to change, and prevention and cure will be that many more years away.
Many seniors depend on the American Association of Retired Persons (AARP) to lobby Washington on their behalf, but the AARP follows a policy of not addressing any one disease. That means there is no major voice in Washington telling Congress that macular degeneration research is important to Americans. Write your representatives in Congress and ask them to support the NEI and promote additional funding for macular degeneration research. Fortunately, ARMD has been in the news enough that they should understand the urgency of your request.
Newsweek, Time, Prevention, US News and World Report, The New York Times, and CNN have all reported on new studies since early 1996. News reports, however, are not always entirely complete. While celebrating and encouraging scientific breakthroughs, the media have a tendency to trumpet results prematurely. Experimental treatments and special curative diets are sometimes presented as if their success has already been confirmed. The hopes of many combined with the relative lack of public information on the topic (at least until 1999) give these news reports great weight. Patients often call to ask about new cures and requesting treatments that haven't really been proven effective or safe. The truth is that macular degeneration is complicated; there is no easy answer. Chapter 2, "ARMD Treatments and Medical Research," and Chapter 3, "Genes and Greens: The Causes and Prevention of ARMD," accurately explain the latest information on research, treatment, and prevention. It is important to understand what we really
do and do not know, and it's also important to keep faith in the future since it will hold new solutions.
Macular Degeneration Isn't Just About Your Eyes
Unfortunately, few authorities recognize that ARMD affects more than a person's eyes. Most people say they'd rather lose a limb than an eye, and national surveys tend to place vision loss among the most feared afflictions, along with cancer. Why? Because eyesight affects every aspect of life: mobility, physical activity, communication, appearance, perception, self-esteem, and psychological health. Macular degeneration is not just about how much you can or cannot see. It's about your whole life: how you cope with change, your view of the future, and your capacity to enjoy the present. And macular degeneration is tailor-made to push every button we have. It can raise feelings of grief, helplessness, depression, fear, anxiety, and anger. This book seeks to address these experiences in Part II, but first we have to define the condition itself. As Zelda put it, "macular what?" What is macular degeneration anyway?
AGE-RELATED MACULAR DEGENERATION EXPLAINED
Our Eyes Are Like Little Cameras
You have probably heard this analogy before: our eyes are like little cameras.
Just as light enters the camera through the shutter, is focused by the lens, and falls on the film, so light enters our eye through the pupil, is focused by the lens, and falls on the retina at the back of our eye. The retina is like camera film. Its thin tissue forms the inner lining of the eye, picking up light and converting it into nerve signals. The retina sends those signals through the optic nerve to the brain, which "develops" them into the images we actually see, just as film is developed into photographs.
The Macula: Center of the Retina
The retina has two types of photoreceptor cells that convert light into electrical messages for the optic nerve to transmit: rod cells and cone cells, so named for their shapes. There are many more rods than cones throughout the retina, especially at the edges, where rods outnumber cones twenty to one. Rod cells are responsible for peripheral vision and light-and-dark contrast perception. They essentially provide us with background information, but they cannot transmit crisp pictures. We use the rods of our peripheral vision to catch a glimpse of something. They tell us that a car is coming from the far left or right, but in order to see the car clearly or describe it, we instinctively turn to look at it directly. As soon as we turn, however, we are no longer primarily using our rod cells to see, but our cone cells. Cones are concentrated in the center of the retina--called the macula--and are responsible for central vision, color perception, and sharp images (acute vision). The capacity of cones to distingui
sh detail is one hundred times greater than rods. We need them to tell the difference between forest green and black, and to see precise detail, like the features of a face, the lace pattern on a table cloth, or the letters on this page. The macula is therefore both the geographic center of the retina, and the focal center of our vision. The fovea is the very center of the macula. It is also the only area of the retina that has only cone cells. For all its power, though, the macula is very small; it measures about a quarter inch in diameter and is tissue-paper thin. But the macula is truly a mouse that roars. This tiny area is responsible for so much of what we see.
Macular Degeneration: The Key Players
In macular degeneration, rod and cone cells of the macula begin to die, reducing the number of cells able to transmit visual signals to the brain. Macular degeneration, however, is not a condition of these cells alone, but of the underlying tissue that supports them and keeps them healthy. In addition to the rods and cones, there are three more key players in macular degeneration: the retinal pigment epithelium (RPE), Bruch's membrane, and the choroid. In that order, each is a layer of tissue that lies beneath the retina, like layers of a club sandwich or, more accurately, stations on a delivery line. Taken together, they form a kind of conveyor belt for nutrition and waste management, constantly supplying the macula with oxygen-laden macula meals and whisking away waste. The large blood vessels of the choroid truck materials in and out through the blood stream. Bruch's membrane acts as a security gate between these blood vessels and the delicate RPE, and the RPE delivers oxygen and receives waste directly fr
om the rod and cone cells in the macula.
Normally, the system works very efficiently. But if there's a jam somewhere, the oxygen meal shipments and the waste removals back up, and eventually the pick-up and drop-off stations shut down. The choroid, Bruch's membrane, and the RPE become disabled and can no longer do their jobs. When they fail, the rod and cone cells lack the massive amounts of oxygen they need to stay alive and have no way to clear away the waste products they produce by metabolizing oxygen. Dying of oxygen deprivation and clogged with refuse, rods and cones become unable to send signals through the optic nerve to the brain--they are no longer able to see. This is what happens with macular degeneration.
TWO TYPES OF ARMD: DRY AND WET
There are two types of macular degeneration, commonly called dry and wet. All cases are thought to start with the dry form. Between 10 percent and 15 percent of the people who show signs of dry macular degeneration eventually develop the wet form.
Although there is only one kind of dry ARMD, you may hear it called "atrophic," "geographic atrophy," or "nonexudative" macular degeneration. Atrophic or atrophy refers to a declining, weakening, or wasting away. We often use the word to talk about muscles that haven't been used in a great while and lose their strength as a result. We can exercise our muscles and regain strength but, unlike our muscles, atrophy in our macula isn't currently reversible. This is because the macula atrophies from a lack of oxygen, not a lack of use. And as we know, any part of our body that suffers a prolonged lack of oxygen usually sustains permanent damage. Geographic atrophy of the macula means atrophy concentrated in one contiguous area of the macula. Nonexudative means not exuding, or not discharging, meaning that there is no blood leakage in the macula contributing to the malfunctioning of the conveyor belt system.
Hard and Soft Drusen
Dry ARMD is usually signaled by the presence in the macula of small pale spots called drusen. There are two types of drusen: less harmful hard drusen and more ominous soft drusen. Hard drusen are small, round, sharply defined light yellow deposits of lipid (a fatty compound) and calcium that accumulate on Bruch's membrane. They are quite common with age, appearing in most older eyes like age spots appear on skin, and are not necessarily thought to indicate macular degeneration. Soft drusen can be nearly twice the size of hard drusen, with indistinct margins and varying sizes and shapes. While soft drusen can be seen in older eyes that don't develop full-blown ARMD, they have been considered an early indicator of the condition, perhaps because they are the first feature of ARMD that we can detect in an affected eye. Recently, however, researchers have suggested that by the time we can see soft drusen in an eye, macular degeneration may already be advanced.
Soft drusen are thought to plug up the conveyor belt system in dry macular degeneration. Some researchers also believe that soft drusen are responsible for wet macular degeneration because they may weaken Bruch's membrane or because they may trigger the proliferation of abnormal blood vessels. Other researchers disagree, arguing that soft drusen occur because Bruch's membrane has already been weakened for some other reason. In any case, soft drusen signal to us that the conveyor belt support system for the macula is malfunctioning and Bruch's membrane is weak, which may allow abnormal blood vessels from the choroid to creep through. Your ophthalmologist can see hard and soft drusen in your eyes during a standard eye exam, with no special testing. Your retina is transparent, although it appears red-orange because the underlying RPE gives it color. The light yellow color of the drusen shows up against this red-orange glow.
Like soft drusen, focal hyperpigmentation is another signal of possible early macular degeneration that your ophthalmologist can see. Focal hyperpigmentation means the appearance of darkish irregular specks in the macula. They are caused by pigment cells that clump up over time, although we aren't sure exactly why they do. When our eyes are young, healthy, and working well, they have a kind of robust color, like a rosy apple. The RPE glows bright red-orange, and the fovea, the center part of the macula, has a pretty gold glow. But when our eyes become much older or unhealthy, they appear sallow. Light yellow drusen tone down the bright red-orange of the RPE, and darkish pigment specks mark the gold of the fovea. Since age-related macular degeneration is a condition of deterioration, these age spots, like drusen, are often indicators of oncoming macular degeneration.
Wet ARMD is called "wet" because it is characterized by abnormal, leaky blood vessels that grow underneath the retina in the choroid. You may also hear wet ARMD called "subretinal net," "subretinal neovascularization" (SRNV), or "choroidal neovascularization" (CNV). Subretinal means "underneath the retina" or "underneath the RPE," and neovascularization simply means "new vessels." Wet ARMD may also be referred to as exudative degeneration. Exudative means "seeping" or "bleeding," referring to these abnormal blood vessels. We don't know why these abnormal blood vessels grow. They grow from the choroid through Bruch's membrane, which is not supposed to allow such a thing, and collect under the RPE like tree roots under a sidewalk. These vessels are weak and tend to leak fluid and blood, which seeps through the surrounding tissue, flooding the cone cells of the macula and either suffocating them or triggering changes that result in their death. Very late stage wet macular degeneration is sometimes called discifo
rm degeneration. Although this refers to the disc-shaped scars that result after bleeding occurs, disciform degeneration is generally used to simply refer to extensive or late stage degeneration.
If these leaky vessels exert enough pressure under the RPE, they may rip it away from Bruch's membrane, creating a sort of blister between the two layers that permanently destroys the conveyor belt system in that particular area. This condition is called a serous pigment epithelial detachment, or PED. A PED is sometimes referred to in patient information pamphlets as a third type of macular degeneration, but it is a possible development in wet macular degeneration.
Your ophthalmologist may be able to detect the presence of abnormal blood vessels in your eye because they sometimes give the affected area of your retina a muted gray-green color. But to define the precise size and shape of these vessels, a fluorescein angiogram is necessary. This is a photograph of your eye taken with a special camera that can detect dye in the blood vessels underneath your retina. Having a fluorescein angiogram involves having dye injected into your arm. This dye travels throughout your blood stream, making all of your blood, including the blood in those abnormal vessels, glow for the camera. Chapter 2 provides a more detailed explanation of fluorescein angiograms and treatments for macular degeneration.
ARMD DOES NOT AFFECT PERIPHERAL VISION
Macular degeneration is by definition a condition affecting only the macula--not the entire retina. It is a failure of the conveyor belt system that exclusively supports the macula, which has a very different support system from the rest of the retina. This is because the macula is the only area of the retina with a high concentration of cone cells, and cones turn out to be very high maintenance. They demand enormous quantities of oxygen, and produce enormous quantities of oxygenated waste. In fact, the macula has the highest blood flow of any area in the body. Rod cells, on the other hand, consume much less oxygen, so they don't require the same level of support. As a result, rods outside the macula have their own support system. And it doesn't clog up, partly because rods consume less oxygen and produce less waste, and partly because the rods outside the macula are distributed over a much larger area, so there is more support tissue available for each cell. It might help to think of the macula as a busy lit
tle island in the middle of a big, calm retina rod-lake: the macula has its own soil, its own root system, and its own drama of health and survival.
PATTERNS OF ARMD PROGRESSION
Macular degeneration often catches people off guard. Not only does the disease progress painlessly and silently, but our eyes are designed to compensate for one another. If one eye's vision deteriorates gradually enough, the brain simply pays attention to the visual signals of the other eye, allowing us to maximize our vision and avoid the distractions of minor impairments. Buddy Burmester, for example, began to notice that it was more difficult to read the morning paper in his kitchen, so he turned on an extra light or sat in the sun on the deck, without really noticing his own adjustment. It wasn't until street signs became difficult to see at dusk that he thought he might need new glasses. Like Zelda, he was utterly shocked to discover that his eyesight in his right eye was 20/200, at the level of legal blindness, while his left eye was holding its own at 20/50. Buddy's experience is very common.
Visual Indications of ARMD
If you see an ophthalmologist or optometrist who checks your retinas at least every two years, he or she will likely detect early macular degeneration before you experience any significant vision loss. If you do not see an ophthalmologist or optometrist regularly, you will not be able to tell whether or not you have early macular degeneration. Like Buddy, you may not notice anything at all until you experience significant vision loss, especially if your degeneration is advanced in only one eye. You can use the Amsler Grid in Chapter 2 to test your own vision at home, but I recommend checkups with an ophthalmologist or optometrist every two years, not only for macular degeneration but also for glaucoma and for the general health of your eyes. If you do experience vision loss from macular degeneration, you are most likely to notice difficulty reading, seeing small details, pouring champagne or coffee (especially if whatever you are pouring is the same shade as your glass or cup), and distinguishing between simi
liar colors and subtle shades. You may also notice that you need more light to do what you used to be able to do with less light but that you are more sensitive to glare.
Your Risk of Vision Loss from Macular Degeneration
If you have a few soft drusen, which is usually considered a sign of early onset ARMD, you may never develop late stage macular degeneration and significant vision loss. The risk, however, increases with age and with other factors, like eye color, family background, a history of smoking, and nutrition. There are no reliable risk statistics for dry ARMD, which means that we cannot really predict how fast your dry macular degeneration may progress, whether you will get it in both eyes, or what amount of vision you may lose. We can use the Beaver Dam Eye Study statistics, which combine the rates of wet and dry macular degeneration, to give you a ballpark risk figure. What remains clear is that everyone's risk of macular degeneration increases with age. If you are fifty-five, for example, your chance of having early signs of macular degeneration is 13.8 percent and your chance of having full-blown macular degeneration (either wet or dry) is about .6 percent. By the time you are over seventy-five, however, those f
igures jump to 29.7 percent and 7.1 percent, respectively.
What Are the Risks of Developing Wet ARMD in a Second Eye?
Researchers have focused most of their efforts on wet macular degeneration since wet macular degeneration may respond to laser and causes vision loss more quickly and extensively than the dry form. For wet macular degeneration, we have more accurate risk predictions from the Macular Photocoagulation Study. This study addressed a number of specific questions, including: "What are the chances of developing wet macular degeneration in your second eye if you already have it in one eye?" The answer turns out to be: "It depends." It depends upon whether or not you have one or more of four risk factors. They are:
1. Five or more drusen in your second eye
2. More than one druse larger than .064 millimeters
3. Focal hyperpigmentation
4. High blood pressure
Your risk of developing wet macular degeneration in your second eye within five years of the first eye is as follows, according to the study:
Withno risk factors = 7 percent
With 1 risk factor = 25 percent
With 2 risk factors = 44 percent
With 3 risk factors = 53 percent
With 4 risk factors = 87 percent
Now, there's a great deal that these figures don't tell us: how much vision you may lose in either eye, or what your chances of developing wet macular degeneration in the first eye are to start with. What they do tell us is that macular degeneration and vision loss vary greatly from one person to another. We know that you can develop macular degeneration before you experience any significant vision loss from the condition. And, as we know from Buddy Burmester's experience, you can experience significant vision loss before you realize that you have developed macular degeneration. How fast you may experience vision loss and how much vision you will lose depends, but upon what it depends is not yet clear.
As a result, people's experiences of ARMD vary greatly. Buddy Burmester, who has dry ARMD, lost vision in both eyes within four years from the time of his diagnosis. He still reads with the help of a closed circuit television, but he doesn't drive. Zelda Grant turned out to have fast progressing wet ARMD and experienced pronounced vision loss in less than six months. But their neighbor, Dolores Lopez, was diagnosed with dry ARMD in one eye nearly eight years ago, and she's still using the other eye to drive and read. Why is Dolores's macular degeneration progressing so much more slowly than Buddy's? Why didn't she develop wet macular degeneration like Zelda did? We just aren't sure. Fortunately, new studies, and even whole new centers devoted to macular degeneration research and treatment, are appearing even as you read this book. With increased attention to the condition and more research money, we will have better answers to these questions. We may also find effective ways to slow the progress of ARMD or pr
event it altogether.
LATE STAGE ARMD
Given that we can't predict how macular degeneration may affect any particular person, what is the worst case scenario? Now that Buddy's and Zelda's macular degeneration has affected both of their eyes, how much vision can they expect to lose in the long run? How bad does it get? What exactly does "developing vision loss" mean anyway? The phrase sounds like a polite euphemism, largely because we have an impoverished vocabulary for talking about visual impairment. Until very recently, our options were to talk about having normal vision or being blind, with the confusing third term "legal blindness" in the mix.
The good news is that Buddy and Zelda will not become totally blind from macular degeneration, and neither will anyone else. If you have ARMD and no other eye condition you will always have your peripheral vision. This sight is yours to keep, a saving grace that will enable you to always maintain a level of independence and to enjoy activities that require some vision. This is a fact, but it's a fact that many people with vision loss often doubt. When my daughter set out to interview several of my patients for this book, she discovered that at least 50 percent questioned my enthusiastic assurances that they weren't going totally blind.
At first I thought that maybe I hadn't communicated my assurances strongly enough. Then I realized that the very nature of macular degeneration fosters this doubt. As I've admitted, we don't know a great deal about its causes. And if physicians don't know exactly what causes the development of soft drusen or the proliferation of abnormal blood vessels in the macula, then how can they guarantee that total blindness from macular degeneration isn't a possibility? The answer is that this guarantee is built into the anatomy of your eye. As I explain in greater detail in the section above entitled "ARMD Does Not Affect Peripheral Vision," macular degeneration by definition is specifically a degeneration of the macula--not the entire retina. The rod cells that provide your peripheral vision and are located outside the macula remain unaffected by macular degeneration.
The Fear of Total Blindness
The fear of total blindness many people express may stem from the experience of having macular degeneration itself. Since ARMD is a degenerative condition, it subjects those who have it to the frustrating process of watching their eyesight slip away. Each degree of vision loss may feel like a threat to daily life, creating a timed progression that measures one year against the previous one, one day against the next. Last year I could read the newspaper, this year I cannot. Tomorrow the salt shaker will disappear. It's enough to drive even the most stalwart personality nuts. It is also enough to give the very real impression that there is no end, that the deterioration will continue endlessly until there is nothing left to lose. This impression becomes stronger as the condition progresses because the majority of remaining vision is peripheral, and peripheral vision is not very precise. As a result, it becomes more difficult to tell whether or not one's vision is as good today as it was yesterday. The remaining
peripheral vision also feels very precarious, like the last lone cowboy standing on an exposed bluff. And it feels inadequate compared with fully functioning central vision.
"How much more vision can I lose and still see?" This is the question that many patients would like to throw at their doctors' assurances that they are not at risk of total blindness. What, in other words, is the practical difference between what you are calling total blindness and what I'm seeing, or more precisely, what I'm not seeing? The practical difference is enormous, especially if you work to enhance your remaining eyesight through visual rehabilitation. Vision that is 20/400, while not close to 20/20, is a great deal more sight than we commonly call blindness. My 93-year-old father has 20/500 vision in his best eye from macular degeneration. He bowls in a league, writes his own checks, and dines out regularly. He recently took a bus up to the frame shop, had his favorite photograph enlarged, gave instructions for cropping it, and selected a matching silver frame. And then he walked home. That's a lot more than he could do if he truly couldn't see anything at all.
OUR VOCABULARY OF VISION
We often think of 20/20 vision as perfect sight. We say "hindsight is 20/20" or we name a truth-finding television program 20/20. The truth is that 20/20 vision is not perfect vision but standard vision, or the lowest amount of vision that is considered normal (many people have better than 20/20 vision). The first 20 represents you standing twenty feet away from an object. The second figure, in this case also a 20, represents how far away from the object a person with standard normal eyes could stand and still see it in the same amount of detail as you do. In other words, if your vision is 20/60, it means that what you can see from a distance of 20 feet, the average person with normal eyes can see from a distance of 60 feet. We can take Buddy Burmester as an example. When he discovered that the vision in his right eye was measuring 20/200, it meant that he could see at 20 feet away what his wife or daughter could see in the same detail at 200 feet away.
This figure, however, doesn't give a complete picture of the quality of Buddy's vision or of our own. There are a whole host of other variables that go into measuring visual acuity that the figures 20/60 or 20/200 don't represent. For example, 20/60 doesn't measure visual ability in varying weather or lighting conditions, and it doesn't measure color perception or contrast sensitivity. The only other measure that has gained as widespread a use as the 20/20 measure is the field measure. The average normal eye has a visual field of roughly 170 degrees, or a little less than a half circle. This means that when you look straight ahead and stretch out your arms to either side, you can see from the tip of one hand to the tip of the other out of the corners of your eyes. This is the rod cell peripheral vision that people with macular degeneration keep.
Vision Exists on a Continuum
Using the 20/20 measure as our sole vocabulary for vision is misleading because it suggests to us that seeing is an all-or-nothing proposition, rather than a process. We talk about whether we have 20/20 vision or not. We measure our sight based on a number we get from the optometrist's or ophthalmologist's office rather than on what we can accomplish with our eyes. We fall into thinking that there are two categories of people in the world: those who can see and those who can't, or the normal and the blind. But vision exists on a continuum, like hearing or feeling pain. Whenever we experience pain we are aware of its quality and intensity. Doctors often ask, "On a scale of one to ten, how much back pain do you feel?" We think of hearing on a relative scale, too. Music that one person experiences as too loud, another may experience as not loud enough. When someone says they are "hard of hearing" we accept that they have some amount of hearing loss, but we aren't sure how much--it depends upon the individual. Th
is variation is true of vision, too.
Lorraine Marchi, a pioneer advocate in the field of low vision and the founder of The National Association for the Visually Handicapped (NAVH), coined the term hard of seeing as a more accurate description for most types of vision loss than the word blind connotes. Many blind people perceive some light, and may recognize light sources, or even see some hand motion. People with low vision see much more than hand motion, but less than about 20/60. That's a very big range. We need to get used to thinking about low vision, rather than perfect vision versus blindness. Low vision includes a wide range of visual ability that is less than 20/20 but more than blind. Simply, as Mrs. Marchi says, it's "hard of seeing."
Using low vision avoids the limitations of other terms like 20/20, blind, or legally blind. And the term approximates what is actually going on, which is the presence of vision with impairment. It's a term we can use to talk about the varieties of vision that people experience, rather than continually struggling with the twin poles of perfect vision and total blindness. Because the term is new, and covers such a wide range of visual abilities, low vision is defined slightly differently by various health, government, and private organizations. Insurance reimbursement policies and state regulations differ quite a bit. For example, many states require 20/40 vision or better for an unrestricted driver's license, while others allow people with vision of 20/100 to drive. The National Eye Institute (NEI) eschews a particular acuity measurement for low vision, recommending instead that low vision be defined in terms of ability. We ought to be asking, in other words, whether or not someone can read a newspaper, or a c
anned goods label, or recognize a friend on the street when we seek to assess low vision.
Legal blindness does not mean total blindness. The term legal blindness appeared during the Great Depression. It was originally called economic blindness and was an arbitrary measure set by the government to determine which citizens would find it difficult to get employment as a result of impaired vision. Special economic relief programs were initiated for the people who qualified. The government designation of legally blind still stands today, and if you qualify you are entitled to a number of helpful programs and bene-fits detailed in Appendix II. Legal blindness is defined as having 20/200 sight in your best eye with correction, or a visual field of 20 degrees or less. This means that with glasses or contacts you can see at 20 feet with your best eye what a normal eye sees at 200 feet, or that your sight encompasses an area that is 20 degrees wide rather than 170 degrees. More than 85 percent of the people who qualify as legally blind have some functional vision; only 15 percent are completely blind. As wi
th the 20/20 measure itself, legal blindness is an arbitrary point selected for public policy purposes. It's a great idea, but it doesn't give us details about the people who fall into the category of legally blind, many of whom have jobs that require sight. There are many people who are legally blind who absolutely do not consider themselves blind.
GLAUCOMA, CATARACTS, AND MACULAR DEGENERATION
Finally, people often ask me if glaucoma, cataracts, or diabetic retinopathy aggravate macular degeneration, or if macular degeneration aggravates any of them. The answer is no. Glaucoma, cataracts, and diabetic retinopathy are unrelated to macular degeneration. ARMD is not directly related to any other disease or eye condition to our knowledge. There is some new evidence that cataract surgery may affect macular degeneration, although these findings have not been widely confirmed. Chapter 2 discusses this possible relationship in greater detail. To understand why glaucoma, cataracts, and macular degeneration are unrelated, it may help to return to our original picture of the eye and clarify how each of these conditions causes vision loss.
Cataracts are opacities of the lens at the front of the eye. They prevent images and light from entering the eye, somewhat the way sheer curtains block the view through a window. Cataracts can usually be surgically removed and replaced by new lenses.
Glaucoma is a condition of high pressure inside your eye that damages your optic nerve. Your eye is a closed, fluid-filled system. If too much fluid accumulates, pressure inside the eye rises, pushing on the optic nerve and gradually damaging its delicate fibers. If detected early, glaucoma is easily treatable in most people with prescription eye drops, laser, or surgery. If untreated or uncontrolled, glaucoma can cause peripheral vision loss and eventually complete blindness.
Diabetic retinopathy is a condition caused by diabetes in which the retina may be swollen and abnormal blood vessels may develop on the surface of the retina. These vessels can bleed or constrict and cause retinal detachment. Diabetic retinopathy can affect the entire retina, resulting in different degrees of vision loss. It is treatable with laser in most people if identified early enough. You cannot get diabetic retinopathy if you do not have diabetes. People with diabetes have a higher incidence of glaucoma and cataracts, but not of macular degeneration.