Coping with Vision Loss: Maximizing What You Can See and Do
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Coping with Vision Loss: Maximizing What You Can See and Do
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Product Details
| ISBN-13: | 9781630265144 |
|---|---|
| Publisher: | Turner Publishing Company |
| Publication date: | 03/27/2001 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 304 |
| File size: | 2 MB |
About the Author
Dr. Lin Moore is a low-vision specialist and a professor at the Northeastern State Universityof Oklahoma School of Optometry.
Read an Excerpt
Coping with Vision Loss
Maximizing What You Can See and DoBy Bill G. Chapman
Hunter House Inc., Publishers
Copyright © 2001 Bill ChapmanAll right reserved.
ISBN: 978-0-89793-316-2
Chapter One
Visual Acuity
Visual acuity notation - the pair of numerals that tell you how well (or otherwise) you can see - will be used in this book, so readers need to know exactly what the numbers mean. With this knowledge, a person with a degenerative disease can keep track of his or her vision loss.
A legally blind person has a visual acuity of 20/200 or worse, which would be indicated by a second number larger than 200, for example, 20/350. Just what do these numbers mean?
Notice that the numbers are written as a fraction. They consist of a numerator and a denominator. The numerator, or first number, is usually 20. This refers to 20 feet - the distance we sit from the test chart when the doctor tests our vision. The standard is to use 20 feet, but when working with persons who have subnormal vision, doctors sometimes use 10 feet, 5 feet, or even 1 foot. The distance in feet between the patient and the test chart becomes the numerator of his or her visual acuity.
The denominator, or second number, refers to the size of the letters on the test chart. They are a very specific size. If a letter is the 200-size, it means someone with normal vision (20/20) can read that size letter from 200 feet away. A person with normal vision can read 60-size and 120-size letters from a distance of 60 and 120 feet respectively.
The big "E" at the top of the test chart is usually a 200-size letter. A visual acuity of 20/200 means that while one person must sit 20 feet from the chart to read the big "E," someone who has normal vision can sit 200 feet from the chart and read the same-size letter. Neither of them would be able to read a smaller-size letter from these distances: keep this in mind while reading the book.
The following is key to understanding visual acuity. A person standing 20 feet from the chart who reads the 200-size letter will be able to read a 100-size letter when he moves to 10 feet from the chart. So, 20/200, 10/100, 5/50, and 2/20 all indicate the same visual acuity. The ratio between the numerator and denominator is 1/10 in all these cases. This concept is discussed more fully in Chapter 13.
The reader should understand that this material is theoretical. For certain persons with low vision the results will not be as mathematically precise. However, the fact remains that the closer one gets to the chart, the smaller-size letter he or she is able to read.
"Legal Blindness" Defined
Some doctors vehemently reject the use of the word "blind" when talking about persons who are partially sighted. I understand and agree with this position, which emphasizes that a person who is partially sighted is not "blind." This perspective accentuates the fact that any remaining vision is useful. I also accentuate the positive view that persons with visual impairment still have useful vision, but I recognize the need to educate people as to the meaning of the word "blind."
The word "blind" may call to mind a person walking down the street with a white cane or a guide dog, but "blind" is a legal term. There are two ways a person can become "legally blind."
Loss of Visual Acuity
There are varying degrees of vision loss. Years ago, authorities arbitrarily drew a line: If one's visual acuity dropped below a certain level, he or she was declared blind. Since most people classified as "blind" enjoyed some remaining useful vision, the term "legally blind" evolved as a way of distinguishing them from the totally blind, who have little or no light perception.
Notice that the line drawn implied that such people's vision was nearly useless. Even today, this attitude persists and may explain why many doctors "write off" patients whose vision drops to this level.
At one time, states used different definitions of legal blindness. Some used a visual acuity of 20/400, while others used 20/200. Because the federal government pays 80 percent of rehabilitation costs for the blind, most states eventually adopted the federal standard of 20/200 so they could qualify for federal funds. Some states refer to legal blindness as "industrial blindness." This term also implies that vision below 20/200 is useless, in this case, for employment.
If the reader understands nothing in this book other than this one point, he has not wasted his reading time. Legal blindness does not mean a person is helpless or useless; it means he has a problem. With knowledge and help, that person can cope with the disability and can function with the vision he has left.
Field Loss
Visual acuity is only one measure of legal blindness. Retinitis pigmentosa and glaucoma can destroy peripheral vision, leaving only a 1-degree field of vision, which limits a person to seeing only straight ahead. (By contrast, a normally sighted person has a 180degree field of vision.) The law states that a person whose visual field measures 20 degrees or less is legally blind regardless of her visual acuity. So, if someone's field of vision has been reduced to 1 degree, even if that 1 degree is 20/20, the person is considered legally blind.
How Test Charts Mislead
When I first began to lose vision and to take an interest in this subject, I encountered many people with a visual acuity of 20/200. But I never met anyone with a visual acuity of 20/150 or 20/175. This is because of a problem built into standard eye test charts.
Letter sizes on the typical eye test charts increase in units of 5 feet, jumping from 20, to 25, 30, 35, 40, and so on. After 80, the chart jumps 20 feet to 100. From there it jumps to 200, then to 400! Letter sizes larger than 400 are rarely found, except on special charts used in testing persons with subnormal vision.
Since the standard charts fail to discriminate between letter sizes, persons with a true visual acuity of 20/120, 20/150, or 20/180 are all diagnosed as 20/200. The doctor concludes, "This patient can't read the 100-size letter. The next size available is the 200-size, so that is how I must diagnose him." The same problem exists between 200 and 400.
Because of this inadequacy in the charts, persons with a visual acuity worse than 20/100 but better than 20/200 are all diagnosed as 20/200. Likewise, persons worse than 20/200 but better than 20/400 are all said to be 20/400.
A significant difference exists between the measurements of 20/105 and 20/200. Teachers are sometimes puzzled by the differences in performance of students who are all diagnosed with a visual acuity of 20/200. The student who is truly 20/105 will perform better than one who is 20/140. Both will outperform the student who is a true 20/200, yet all three are likely to have a doctor's report measuring their visual acuity as 20/200.
There is another variable related to performance and visual acuity. Tests can show that two people have the same visual acuity, yet they might perform differently. This introduces the subject of "functional vision." Functional vision relates to how well a person uses his or her residual vision. Time after time, I have met persons who say, "Your vision must be better than mine because I can't drive," or "I can't see TV," or "I can't read." When I've tested their visual acuity, I've often found that my vision is actually far worse. The difference is that I have learned to use my remaining vision better than they use theirs. My "better" performance can be attributed to vision rehabilitation - and enhancing performance through vision rehabilitation is what this book is all about.
Doctors may not be able to cure the disease that is destroying a person's vision, but the effects of the disease can be overcome or greatly minimized. These people can learn to function better, and the difference in performance is often dramatic. This is why a person's mindset and emotions play such an important role in vision rehabilitation. One's mindset and emotional state, as they relate to vision loss, can either block or boost all attempts at vision rehabilitation.
These facts are some of the most difficult for those with vision loss to accept. All their lives their eyes have worked. No special effort was needed to make them work. Then, when visual impairment occurred because of disease or accident, the situation changed. They must now learn to use their eyes in a new way. This book shows you how to use your remaining vision more effectively, but each person must incorporate these coping techniques into his or her own lifestyle.
Visual Impairment Defined
A person with a visual acuity of 20/120 can cope with his or her disability better than a person who measures 20/800. This is obvious even to a novice in the field. A person with a visual acuity of 20/60 has experienced significant loss, but he or she can still get a driver's license in many states. On a practical level, then, what do these visual acuity numbers mean?
There are numerous systems for classifying disability related to visual acuity. The visual disability scale that appears below is my own, and it is about as good, or inadequate, as any other.
First, several terms need clarification. "Subnormal vision" is defined by one's visual acuity after spectacles or contact lenses have been properly fitted. A person with a visual acuity of 20/400 corrected to 20/20 with glasses is not legally blind. The term "legal blindness" refers only to persons who cannot be corrected in both eyes using standard lenses; yet anyone not fully corrected to 20/20 has subnormal vision.
The terms "object vision" and "travel vision" need to be understood. "Object vision" describes the person with visual impairment who can see a brick house but not individual bricks. He can see a tree, but he cannot determine, in many cases, what kind of tree it is or distinguish individual leaves from a distance. He can see a person, but cannot determine whether that person is friend or stranger, even if he can determine the gender. In other words, the person can see enough to identify familiar objects, but he lacks definitive power. He cannot see details.
Early on, I lost the ability to see wrinkles on people's faces. In postgraduate school, one of my professors seemed about thirty-five or forty years old. She had to be around that age, I reasoned, because of her position as department head. A year later, she retired. She was sixty-five! Her face was wrinkled by age, but I couldn't see the wrinkles. I had lost definitive power.
"Travel vision" refers to how well a person can move around independently in an unfamiliar area without help from other people, a white cane, or a guide dog.
A Visual Disability Scale
20/20 - Normal vision.
20/25 to 20/65 - Subnormal vision, but not seriously impaired. Those below 20/45 have difficulty reading a newspaper, but most can hold it closer to their face and still read with good light. Many states will license people to drive with visual acuity as low as 20/60, but most such drivers will carry restricted licenses. Telescopic glasses allow all of this group to drive as long as their state permits it and if they do not also have serious field loss. These people have excellent object and travel vision, except for those who have lost considerable field vision as well as visual acuity.
20/70 - Mildly impaired. This is the point where people really begin to feel handicapped. Reading newspapers is very difficult without magnification, and most states refuse to license persons to drive with a visual acuity this low unless they are equipped with telescopic glasses. Object and travel vision are still excellent, except for those who have lost field vision as well.
20/75 to 20/200 - Moderately impaired. This group can still function as sighted in most regards with the use of low-vision aids. Object vision for this group is poorer, but it is still adequate for almost all activities. These people can see the car but may have trouble identifying its make and model. Recognizing friends may be difficult, but they see the person. Travel vision is still quite good unless there is also field vision loss.
Reading is the primary problem for this group, but good equipment and training eliminate this problem. I knew a young man on a high school football team who played wide receiver with a visual acuity in this range. He saw and caught the ball as well as other team members, but he had problems reading. People in this group can be equipped and trained to read using numerous low-vision aids. All members of this group should be able to drive with telescopic glasses unless there is also serious peripheral-vision loss, or other limiting factors.
Many rehabilitation agencies justify teaching Braille and the use of a white cane to people in this group who have a disease that may ultimately destroy all vision. While such an approach may make financial sense, I strongly support vision rehabilitation as the first step in training at this stage. If people in this group later lose even more vision and need blind rehabilitation, then I support giving them additional training at that point, when they will be more willing to accept it. People with functional vision are typically poor Braille and cane students. I believe that it is unnecessary, ridiculous, and a serious injustice to teach Braille to people in this group. They need to be equipped and taught to use the vision they have left. I have seen people in this group being taught Braille and the white cane wearing blindfolds. Nothing angers me more! They need vision rehabilitation, not blind rehabilitation.
20/200 to 20/800 - Seriously impaired, but still with travel vision and reduced but useful object vision. People in this group can read with low-vision aids of various kinds. In my opinion, those below 20/500 might consider learning Braille, but even then it certainly isn't mandatory. These people will not be able to drive, even with telescopic glasses. Object vision diminishes but is still useful. Travel vision is still adequate, although those at the lower end of the scale may sometimes trip over curbs. Crossing streets can be hazardous for people at the lower end of this scale because they cannot see distant oncoming cars.
I worked with a young woman at Baylor University in Waco, Texas, whose visual acuity was 20/800. She often developed "cabin fever" and wanted to get out of the house. She walked around the block, but dared not cross a street. She simply couldn't see oncoming cars. She was supplied an 8X handheld telescope, which improved her vision to 20/100 (800 divided by 8 - the scope's magnification level - equals 100). It gave her independent mobility in her neighborhood and on campus.
20/800 to 20/1200 - Severely impaired. At this level of visual acuity a person loses travel vision. People suffering a loss of peripheral vision may find a white cane useful or even necessary before this point is reached, but at this stage, use of the white cane becomes necessary, regardless of the cause of vision loss.
Some in this group are able to use very strong magnifiers to read large print. A +50 diopter lens ("diopter" - usually abbreviated as "D." - is the unit of measure of the strength of a lens) will give almost all in this group the ability to read textbook-size print. The reading aid of choice is the video visual aid (discussed in Chapter 22), which enables people in this group to read even small print. Object vision is poor, but any that remains is useful. Telescopic devices can aid in distance viewing.
20/1200 to 20/6000 - Very severely impaired. Many doctors reject the use of visual acuity figures this low. While it is true that letter sizes larger than 700 do not exist on test charts, there are mathematical equivalents. For example, 1/200 is the same as 20/4000 (remember that visual acuity is expressed like a fraction or ratio), which informally equates to the ability to count fingers at a distance of one foot. A visual acuity of 2/200, therefore, equals 20/2000; 4/200 equals 20/1000; and 2/600 (a letter size found on low-vision test charts) equals 20/6000. Doctors categorize this level as the ability to see a hand moving one foot away, without the ability to count fingers.
People in the 20/1200 to 20/6000 group are dependent on the white cane or a guide dog for independent mobility. A video visual aid for reading print is the aid of choice and the only aid that provides visual access to print. (The lowest visual acuity I have ever tested on a person who could still use a video visual aid was 1/700 or 20/14,000.) Voice synthesizers are available that convert print into speech. Persons in this group are legitimate users of such equipment, but such machines are beyond the scope of this book.
(Continues...)
Excerpted from Coping with Vision Loss by Bill G. Chapman Copyright © 2001 by Bill Chapman. Excerpted by permission.
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Table of Contents
Contents
List of Illustrations....................xivAcknowledgments....................xvi
Foreword....................xvii
Introduction....................1
PART I: Vision and the Human Eye Chapter 1: Visual Acuity....................8
Chapter 2: Understanding the Eye....................22
Chapter 3: How We See....................35
Chapter 4: Eye Fatigue and Pain....................43
PART II: Other Things to Know Chapter 5: Emotional Issues....................48
Chapter 6: Doctors....................57
Chapter 7: Perks and Privileges....................67
PART III: Major Causes of Vision Loss Chapter 8: Cataracts....................74
Chapter 9: Diabetic Retinopathy....................79
Chapter 10: Glaucoma....................83
Chapter 11: Macular Degeneration....................89
Chapter 12: Retinitis Pigmentosa....................102
PART IV: Coping Techniques and Equipment Chapter 13: The First Principle: Get Closer....................110
Chapter 14: Eccentric Viewing....................114
Chapter 15: Scanning....................123
Chapter 16: Light....................126
Chapter 17: Contrast Enhancement....................132
Chapter 18: Talking Appliances and Large-Print Products....................135
Chapter 19: Magnification: Make It Bigger....................136
Chapter 20: Low-Vision Aids and Their Use....................139
Chapter 21: How Much Magnification?....................160
Chapter 22: Video Visual Aids....................163
Chapter 23: Elvis andJordy....................169
Chapter 24: Aids for the Computer User....................172
Chapter 25: Special Aids for Field Loss....................176
Chapter 26: Aids for Driving....................179
Chapter 27: Aids for Watching Television....................184
Chapter 28: Aids for Writing....................188
Chapter 29: Handling Money....................190
Chapter 30: Playing Cards (and Analyzing Visual Tasks)....................192
Chapter 31: Reading a Watch....................195
Chapter 32: A Survival Kit....................196
PART V: Specialized Knowledge and Skills Chapter 33: Education....................200
Chapter 34: Driving with Telescopic Glasses: An Introduction....................222
Chapter 35: Driving with Telescopic Glasses: A Training Program....................235
Chapter 36: Misconceptions about Driving with Telescopic Glasses....................249
Epilogue....................262
Appendix A: An Eye Test Chart....................263
Appendix B: Sources of Help....................264
Appendix C: Instructions for Building a Plate Light....................271
Endnotes....................273
Bibliography....................274
Index....................276