Table Of ContentMinute Eye Movement
and
Brain Stem Function
Author
Davis Coakley, M.D., M.R.C.P.I.
Associate Senior Lecturer
Department of Clinical Medicine
Trinity College
Dublin, Ireland
and
Consultant Physician
Department of Geriatric Medicine
St. James's Hospital
Dublin, Ireland
Boca Raton London New York
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' 'His soul seemed hovering in his eyes.
Shelley, Rosalind and Helen, 1, 779.
PREFACE
In this century man has developed extremely sensitive methods of exploring the secrets
of our universe, and signals from objects millions of miles away in space are monitored
routinely by our astronomers. Similar progress, however, has not been made in unravelling
the secrets of the human brain. This is especially true of the most inaccessible areas of the
brain such as the rostral brain stem which contains the centers critical for consciousness.
This part of the brain, by virtue of its anatomical position, has been particularly difficult to
study. However, with the development of new neurophysiological techniques the situation
is gradually changing.
This book describes a technique developed over the last decade which uses minute eye
movement as a monitor of brain stem function. These eye movements are constantly present
in the alert subject even when the eye is apparently still. Very sensitive recording methods
are necessary to detect these movements. The contribution which fine eye movements make
to the visual process has been debated for many years. However, apart from reviewing the
subject briefly, this book is not concerned with this debate. Instead, the book describes a
radically different approach to the subject of minute eye movement and concentrates on the
information which these movements give us about the brain stem.
The opening chapters describe the relevant neuroanatomy and neurophysiology as well
as recording techniques. The following chapters describe the minute eye movement activity
of alert subjects, of sleeping volunteers, of anaesthetised patients, and of patients with brain
damage. The last chapter examines the value of recording minute eye movement when
assessing the prognosis of the unconscious patient and it also examines the potential role of
this technique when diagnosing brain death. The book is based on a thesis entitled Ocular
Microtremor and the Unconscious Patient which the author presented to the National Uni
versity of Ireland for the degree of M.D.
Much of the work on ocular microtremor set out in the following pages could be described
as preliminary observation. No doubt some of the findings and conclusions will be modified
by the research of future investigators. I write this book now in the hope that it will stimulate
such research in this new and fascinating field.
THE AUTHOR
Davis Coakley, M.D., studied medicine at University College, Cork, Ireland. After
qualification in 1971 he worked for three years in hospitals in Cork and Dublin. He sub
sequently worked at the University Hospital of Wales, Cardiff. He became a member of the
Royal College of Physicians of Ireland in 1975, and he was awarded the degree of M.D.
in 1978 for his thesis on ' 'Ocular Microtremor and the Prognosis of the Unconscious Patient' '.
In 1978 at the age of 31 he was appointed Senior Lecturer in the Department of Geriatric
Medicine at the University of Manchester and Honary Consultant Physician at the University
Hospital of South Manchester. In 1979 he was appointed Consultant Physician in Geriatric
Medicine to St. James's Hospital, Dublin, and Associate Senior Lecturer, Department of
Medicine, Trinity College, Dublin.
Apart from his work on minute eye movement, Dr. Coakley has developed a special
interest in stroke disease. He has edited a number of books on different aspects of geriatric
medicine and he has also co-edited the first book on nursing written specifically for doctors.
ACKNOWLEDGMENTS
I wish to acknowledge my gratitude to Dr. John Thomas, now at the Burdenko Institute,
Moscow, who first introduced me to the study of minute eye movement and to Professor
John Pathy of the University Hospital of Wales, who encouraged me throughout my early
studies. My brother, Dr. Terence Coakley, University College, Cardiff, gave me practical
help, and it was he who first suggested that I should write this book. I wish to thank my
secretary, Elaine Stapleton, for typing the manuscript.
My wife, Mary, has shared my interest in eye movement from the beginning of my studies.
She has helped me in numerous ways during the study itself and while writing the book.
Her interest in the work has changed what could have been a burden into an enjoyable task.
I also wish to thank Dr. Veroslav Golda of the Department of Neurosurgery, Hradec
Krávlové, Czechoslovakia, for permission to reproduce Figures 31, 32, and 51.
For My Father
TABLE OF CONTENTS
Chapter 1
The Structure and Physiology of Eye Muscle 1
I. Introduction 1
II. The External Eye Muscle 1
III. The Primary Position of the Eye 1
IV. Structure of Eye Muscle 1
V. Muscle Size 1
VI. Contraction Time 2
VII. The Muscle Fiber 2
VIII. Multiple Innervated Fibers 2
IX. Energy Rich Cells 2
X. Internal Structure 3
XI. Morphological Changes with Age 3
XII. Blood Supply 3
XIII. Nerve Supply 3
XIV. Brain Stem Nuclei 4
XV. Eye Muscle Proprioception 4
XVI. Function of Proprioceptors 5
XVII. Electrophysiological Properties 5
XVIII. Eye Movements During Fixation 5
XIX. Minute Eye Movement and Vision 6
References 7
Chapter 2
Recording Minute Eye Movement 11
I. Historical Background 11
II. Recording Methods 11
III. Methods Using Contact Lenses 12
IV. Corneal Reflection Methods 12
V. Photographic Techniques 12
VI. Electrooculography 13
VII. Transducer Techniques 13
VIII. The Piezoelectric Strain Gauge Technique 14
IX. Recording Through the Closed Eyelid 15
References 21
Chapter 3
The Nature of Ocular Microtremor and the Normal Record 23
I. The Nature of Ocular Microtremor 23
A. Introduction 23
B. Ophthalmoplegia and Absent Microtremor 23
C. Resting Tonus of the Extraocular Muscle 23
D. Electrical Studies on Human Eye Muscle 24
E. Recording from Brain Stem Neurons 25
F. Recording from Cerebellar Neurons 26
G. Studies on Animal Microtremor 26
H. Eyeball Mechanics 27
I. Eye Movement and the Reticular Formation 27
II. The Normal Ocular Microtremor Record 28
A. Introduction 28
B. Microtremor Frequencies 31
C. Low Frequency Base Line Oscillations 32
D. Aging and Microtremor Frequencies 32
References 33
Chapter 4
The Effect of Sleep on Ocular Microtremor 37
I. Slow Eye Movements 37
II. Rapid Eye Movements 37
III. REM Sleep 37
IV. NREM Sleep 37
V. Gross Eye Movement and Sleep Stage 38
VI. Recording Through the Closed Eyelid 38
VII. Minute Eye Movements During Sleep 40
VIII. Electromyographic Studies 42
IX. Alerting Analogy 44
X. Arousal Phenomenon 44
XI. Micronystagmus 45
XII. Transducer Sensitivity 45
XIII. Ocular Microtremor in Sleep and Coma 45
XIV. The Ocular Microtremor Record During Hypnosis 45
References 46
Chapter 5
The Effect of Anaesthesia on Ocular Microtremor 49
I. Introduction 49
II. Results 49
III. Anaesthesia and Extraocular Electromyographic Activity 52
IV. Barbiturates and Ocular Microtremor 53
V. Microtremor Activity During Anaesthesia 53
VI. Ocular Microtremor and Neuromuscular Blockade 54
VII. The Effect of Anaesthesia on the Microtremor of Rats 54
VIII. Assessing Depth of Anaesthesia 54
References 56
Chapter 6
Ocular Microtremor and Brain Damage 59
I. Brain Stem Function 59
A. Introduction 59
B. Ocular Microtremor and Brain Stem Function 59
II. Prognosis of the Unconscious Patient 60
A. Consciousness and Arousal 60
B. Clinical Signs of Brain Stem Dysfunction 61
C. Ocular Microtremor and Coma 62
D. Early Prognosis in Coma 63
E. Ocular Microtremor and the Prognosis of the Unconscious Patient 63
F. Results of Study 63
1. Initial Microtremor Records 63
2. Mean Ocular Microtremor Frequency and Regain of
Consciousness 64
3. Overall Mortality 68
4. Prolonged Survival and the Initial Ocular Microtremor Record .. 70
5. Serial Recording of Ocular Microtremor 70
6. Clinical Responsiveness and Ocular Microtremor 72
7. Pupillary and Corneal Reflexes and Ocular Microtremor 73
8. Ocular Microtremor Activity with an IsElectric EEG and Absent
Calorics 73
9. Low Ocular Microtremor Readings with High Activity on the Cere
bral Function Monitor 73
10. Regain of Consciousness with a Low Initial Frequency Level 75
11. The Overdose Group 76
12. Complete Absence of Ocular Microtremor Activity 76
13. Artifactual Changes in the Record 77
G. Prognosis and Initial Record 79
H. The Value of Serial Ocular Microtremor Records 81
I. Contamination of Records 82
J. Caloric Oculovestibular Test and Ocular Microtremor 82
K. Clinical Signs and Interobserver Agreement 83
L. Ocular Microtremor and Abnormal Motor Signs 83
M. Ocular Microtremor and the Cerebral Function Monitor 84
III. Brain Death 85
A. Confirmatory Tests 85
References 87
Chapter 7
Epilogue 91
Index 93
