Chapter 18 of "Process in Biological Vision"
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Visual Abnormalities & Clinical Electrophysiology in Man James T Fulton Neural Concepts Abstract: The major abnormalities of vision are explored in this Chapter; the organic failures, such as visual snow– “believed to be a hardware failure,” as well as many psychotic failures, such as aura– “believed to be a software failure.” The delineation between organic and psychotic failures in vision was a difficult one. The delineation for some conditions appeared to be almost a continuum. Macular dystrophy is a broadly applied label for a variety of forms of macular degeneration and related disorders, only some of which involve the macula. A variety of examples and causes of macular degeneration are reviewed as to source and prognosis. Nystigmus is reviewed from an organic failure perspective prior to its relevance to reading that is addressed in Chapter 19. Allesthesia, the mixing of sensory inputs within the brain, is addressed. Its unusual advantage is in working mathematical problems where the numbers appear in different colors. Also addressed are a variety of clinical and electrophysiological tests that may be called upon to interpret and diagnose these conditions. The results of several surveys related to Achromatopsia and Visual Snow are summarized. Keywords: aura, Visual Snow, organic, psychotic, hallucinations, after images Achromatopsia, macular degeneration Visual Abnormalities 18- 1 PROCESSES IN BIOLOGICAL VISION: including, ELECTROCHEMISTRY OF THE NEURON This material is excerpted from the full β-version of the text. The final printed version will be more concise due to further editing and economical constraints. A Table of Contents, List of Figures and Index are at the end of this Chapter. James T. Fulton Neural Concepts [email protected] May 23, 2018 Copyright 2008 James T. Fulton 2 Processes in Biological Vision 18 Visual Abnormalities & Clinical Electrophysiology in Man 1 18.1 Background There is a large literature on clinical electrophysiology. The recent text by Heckenlively & Arden covers the field from the more academic perspective2. Ryan, et. al. provide a comprehensive summary of the clinical and medical perspective of the retina, including electrophysiology3. Trobe has provided an extensive survey of the neurology of vision4. However, it only addresses achromatopsia and several other areas superficially. The field has suffered from lack of an adequate model of the visual system. This is highlighted by the content of both of the above volumes. Their discussions of the mechanisms of vision are strongly rooted in the conventional wisdom of vision dating largely from the 1950's. The field of clinical eye disease treatment is strongly influenced by the pedagogical environment. As late as 1993, Chawla made the following statement in the second edition of his text5. “At the root of ophthalmic teaching lies the assumption that every syndrome is crowned with a unique fundal appearance.” Chawla focuses on the “Seven Signs,” the physical abnormalities visible with an ophthalmoscope. While the field does recognize the potential for chemical imbalances, it does not give significant credence to the potential for neurological abnormalities not observable by physical deformations. In the same time period while discussing unexplained visual field losses, Burde, Savino & Trobe6 presented a more modern view that is contrary to that of Chawla. “Retinal diseases that cause visual field defects may not produce ophthalmoloscopically obvious abnormalities.” They speak of lesions or tumors found topologically beyond the retina and eye. However, the increasing knowledge of the neural system and genetics leads to a wide variety of conditions unrelated to physically observable causes of disease. By 1999, Chawla was participating in the recent and continuing revolution7. He opened his third edition by saying the following. “The main obstacle to learning anything about the eye is ophthalmology itself. Its jargon obscures even the simplest idea and the quaintly named disorders are frequently taught as a mixture of pathology and therapeutics, with presenting features hidden somewhere in the middle.” A major problem may focus on the definition of ophthalmology itself. The field appears to encompass the medical treatment of diseases of the eye associated with physically observable mechanisms. It has not in the past addressed neurological diseases other than to lump them under the title, psychogenic issues. While, Burde, Savino & Trobe included the prefix neuro- in their title, the subject is only addressed by superficially describing the neural paths associated with the pointing system of the eyes. While this work is not clinically oriented, it does reflect pertinent facts drawn from the broader clinical literature. 1Released June 5, 2018 2Heckenlively, J. & Arden, G. ed. (1991) Principles and practice of clinical electrophysiology of vision. St. Louis, MO: Mosby Year Book 3Ryan, S. ed. (2001) The retina In three volumes St. Louis, MO: Mosby 4Trobe, J. (2001) The Neurology of Vision. NY: Oxford University Press 5Chawla, H. (1993) Ophthalmology, 2nd Ed. NY: Churchill Livingstone pg 46 6Burde, R. Savino, P. & Trobe, J. (1992) Clinical Decisions in Neuro-Ophthalmology, 2nd Ed. St. Louis, MO: Mosby Year Book, pg 1 7Chawla, H. (1999) Ophthalmology, 3rd Ed. Oxford: Butterworth-Heinemann preface Visual Abnormalities 18- 3 Zillmer,et al. have provided the current text neuropsychology8. Part One provides a historical review of early surgeries involving the neural system. Part Two provides an overview of the neural system and the principle sensory modalities (including many aspects of visual abnormalities) from the psychologists perspective. Part Three discusses disorders of the brain, again from a psychologists perspective. The work includes many interesting figures. They are not particularly relevant to the study of the neural system at the functional, or specific features and performance, levels. Lambert & Kinsley have also provided a text on clinical neuroscience that can be quite useful when discussing visual abnormalities9. It appears to cover a broader range of conditions than Zillmer et al. and provide more definitions of terms. According to Webster’s Medical Dictionary, A disease; 1. is an impairment of the normal state of the living animal or plant body or one of its parts that interrupts or modifies the performance of the vital functions, 2. is typically manifested by distinguishing signs and symptoms, and 3. is a response to Cenvironmental factors (as malnutrition, industrial hazards, or climate), Cspecific infective agents (as worms, bacteria, or viruses), to Cinherent defects of the organism (as genetic anomalies), or Ccombinations of these factors. A symptom of a disease is subjective evidence of disease or physical disturbance observed by the patient <headache is a symptom of many diseases> <visual disturbances may be a symptom of retinal arteriosclerosis>; broadly : something that indicates the presence of a physical disorder. A symptom complex is a group of symptoms occurring together and characterizing a particular disease <the symptom complex of epilepsy> A syndrome is a group of signs and symptoms that occur together and characterize a particular abnormality. Unfortunately, the term syndrome is frequently used rather casually to include any group of symptoms that a practitioner decides to group, regardless of whether they exhibit any common source. One syndrome of interest in this Chapter has recently gained prominence, halucigenic persistent perception disorder (HPPD). A chromosome is any of the usually linear bodies of the cell nucleus of eukaryotic organisms, the usually circular bodies of prokaryotic organisms (as bacteria), or especially in some schools of molecular biology the genomes of DNA viruses (as bacteriophages) that take up basophilic stains and contain most or all of the genes of the organism. A gene is a specific sequence of nucleotides in DNA or RNA that is located usually on a chromosome and that is the functional unit of inheritance controlling the transmission and expression of one or more traits by specifying the structure of a particular polypeptide and especially a protein or controlling the function of other genetic material (see expanded definition below). –Phobia is a noun combining form representing an abnormal fear, or an intolerance to or aversion for some situation <photophobia>. The definition of a trait in Webster’s Medical Dictionary is not adequate and will be expanded here. 8Zillmer, E. Spiers, M. & Culbertson, W. (2008) Principles of Neuropsychology, 2nd Ed. NY: Barnes & Noble 9Lambert, K. & Kinsley, C. (2011) Clinical Neuroscience, 2nd Ed. NY: Oxford Univ. Press 4 Processes in Biological Vision A trait is an inherited characteristic. Such traits can be organized into levels of significantly different importance. A high level trait represents the presence of an entire appendage. (Lee, 2004). Alternately, a trait can represent the dimple on the cheek of an individual. It can also represent any of a wide variety of conditions leading to what are described as genetic diseases. The failure of an organism to produce an important enzyme leads to a disease. The definition of a gene also requires further definition. During the late 20th Century, it became quite common to speak of a direct connection between a gene and a protein that it caused to be produced. However, it is now clear that the situation is much more complex. Genes can generally be divided into at least (transcription) genes