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Changes with Age in the Eye of the Dog and Hog from Birth to Senility Clarke Lee Holloway Iowa State University

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Changes with Age in the Eye of the Dog and Hog from Birth to Senility Clarke Lee Holloway Iowa State University Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1969 Changes with age in the eye of the dog and hog from birth to senility Clarke Lee Holloway Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Animal Structures Commons, and the Veterinary Anatomy Commons Recommended Citation Holloway, Clarke Lee, "Changes with age in the eye of the dog and hog from birth to senility" (1969). Retrospective Theses and Dissertations. 4659. https://lib.dr.iastate.edu/rtd/4659 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. This dissertation has been microfihned exactly as received 69-15,617 HOLLOWAY, D.V^., Clarke Lee, 1926- CHANGES WITH AGE IN THE EYE OF THE DOG AND HOG FROM BIRTH TO SENILITY. Iowa State University, Ph.D., 1969 Anatomy University Microfilms, Inc., Ann Arbor, Michigan CHANGES WITH AGE IN THE EYE OF THE DOG AND HOG FROM BIRTH TO SENILITY by Clarke Lee Holloway ^ ^ ^ A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of The Requirements for the Degree of DOCTOR OF PHILOSOPHY Major Subject: Veterinary Anatomy Approved: Signature was redacted for privacy. Signature was redacted for privacy. Head of Major De^rtment Signature was redacted for privacy. De^ f Iowa State University Of Science and Technology Ames, Iowa 1969 ii TABLE OF CONTENTS Page INTRODUCTION ' 1 LITERATURE REVIEW 5 General Considerations of Changes with Age 5 in the Eye Changes with Age in the Cornea 8 Changes with Age in the Sclera 17 Changes with Age in the Iris 19 Changes with Age in the Ciliary Body 21 Changes with Age in the Choroid 24 Changes with Age in the Lens 27 Changes with Age in the Retina 31 MATERIALS AND METHODS 39 Anamnesis of the Experimental Subjects 41 Collection and Preservation of Tissues 42 Processing of the Tissues 44 Staining Procedures 47 Dimensional Studies and Statistical Analyses 49 Designation of Age Groups 51 RESULTS 53 Bulbus Oculi 53 Cornea 55 Sclera 81 Iris 99 Ciliary Body 114 Choroid 127 Lens 140 Retina 154 DISCUSSION 174 Dimensional Change with Age 174 Fibrotic Changes with Age 185 ill Pigmentary Changes with Age 191 Lipid Deposition 196 Mineralization 200 Vascular Changes with Age 210 SUMMARY 219 LITERATURE CITED 225 ACKNOWLEDGEMENTS 237 APPENDIX A. GRAPHS OF DIMENSIONAL CHANGE WITH 239 AGE APPENDIX B. TABLES OF INCIDENCE OF VARIOUS 332 HISTOLOGICAL AND HISTOCHEMICAL CHANGES WITH AGE APPENDIX C. SCHEMATIC ILLUSTRATIONS AND 358 PHOTOMICROGRAPHS 1 INTRODUCTION Much of the dilemma which has accompanied the evaluation of age changes in ocular tissues, as well as in other organs and tissues, has resulted from the difficulty in precisely defining aging and in­ adequately delineating the processes of normal growth, physiological aging, and pathological alteration. In probing the intricate and oftentimes subtle changes created in biological tissues and organs by the mere existence of the tissue over a prolonged period of time, most investigators have developed a personal concept or definition of aging. Differences in the concepts or phrasing of a definition have generally reflected the individual's scientific approach, either dimensional, morphological, functional, or histochemical, to evaluating age-related changes. Although influenced by a specific scientific method of investigation or the investigator's personal interpretation of aging, each concept or definition as a rule has contributed to a better understanding of the overall process of senescence. In addition, concepts and definitions of aging have indicated the investigator's opinion pertaining to the point of initiation of the process of aging. In a broad sense, Getty (1962) divided the life-cycle of warm-blooded vertebrates into three successive phases; namely, 2 growth, maturity, and senility. Furthermore, Getty (1966), as a result of extensive gerontological studies conducted in the Department of Veterinary Anatomy at Iowa State University, emphasized that unless one knew the normal histomorphological picture at the various age levels it was difficult at times to delineate physiological and pathological changes with age in the body tissue. With specific reference to the eye, Duke-Elder (1938) considered senescent changes as continuous processes which started in the cradle or before and which were determined by heredity, constitution, and the inevitable e:Kects of the continued stress and strain of life upon ocular tissue. On the other hand, Friedenwald (1952) designated only those changes which occurred commonly or universally in the aged eye as senescent changes. A very simple and explicit interpretation of aging as related to the eye was presented by Francois (1958). Francois proposed that aging was an early biological phenomenon which consisted of a progressive alteration of the tissue to the extent that there was a marked difference in the anatomy of the eye in the young and in the aged. In accord with the broad concepts of aging as proposed by Getty, Duke-Elder, and Francois, the goals and objectives of this study were formulated to determine the progressive changes which occurred in 3 the eye of the dog and hog from birth to senility. Initially, it was considered imperative to ascertain the specific tissue alterations which occurred during the period of life from birth to the attainment of physical maturity. To designate animals in this age period the term "maturation period" was utilized throughout this thesis; whereas, the term "postmaturation period" was used to designate the period of life from physical maturity to death. The initial determination of tissue alterations which occurred during the maturation period established a basis for evaluating subsequent age-related changes in the postmaturation period. The diverse nature of changes found during the two age periods necessitated the utilization of a number of investigative techniques, each capable of revealing specific information with regard to either the dimensional, histological, or histo chemical alterations attendant with aging. Special emphasis was placed upon determining those changes with age which likely predisposed the constituent tissues of the eye to subsequent functional and pathological alteration. In this regard, an analysis of senescent changes in the vascular components of the eye was considered highly relevant. Hopefully, the findings of this investigation pertaining to the dimensional, histological, and histochemical changes in the eye of the dog and hog with age, will constitute a collected source of 4 information of vital interest to a number of scientists with varied interests in ophthalmology and gerontology. Such information should assist the histologist in more precisely establishing the normal cytoarchitectural variants of the ocular tissues with age and aid the pathologist in the difficult and oftentimes impossible task of delimiting the processes of physiological aging and pathological alteration. A knowledge of the normal progressive tissue changes should benefit the physiologist in assessing the functional changes with age and should be of interest to the clinician in interpreting and explaining various ocular symptoms in the living animal. Information pertaining to senescent changes in the eye of the dog and hog should be of value to investigative efforts in human ophthalmology, since most of the senile changes reported in the human eye (Rones, 1938; Weale, 1963) were present in the ocular tissues of the dog and hog. Admittedly, the broad scope of the present study prevented in- depth investigation of specific age-related changes in the eye of the dog and hog. It is hoped that this overview of ocular changes with age will stimulate and be of value to future in-depth investigations of specific changes with age in the eye of both animal and man. 5 LITERATURE REVIEW General Considerations of Changes with Age in the Eye Susceptibility of the eye to aging According to Schofield (1961), no organ within the human body reflected the process of aging more readily than the eye. The eye, being constructed of many types of tissue each having a peculiar structure, developed senile changes of unusual variability and complexity. Schofield added, these changes were often so subtle and gradually progressive, one was not aware of their moment of onset. Duke-Elder (1938) maintained that the avascularity of certain ocular tissues, an optical necessity, made these tissues prone to degenerative changes, and the lack of inflammatory response associated with avascularity made them peculiarly unresistant to infection. Burger (1958) commented that the avascularity of the cornea and lens rendered these structures of particular interest in the measurement of the aging processes since they do not participate in the usual daily metabolic processes. Tassman (1956) upheld the opinion that all structures of the eye were affected by senescent changes to some degree. Tassman considered most of these changes as more or less benign and, in essence, were part of the general aging process. Francois (1958) 6 agreed that senescent changes, in actuality, were part of some process of a more general nature but emphasized that senile modifi­ cations assumed special characteristics for each ocular tissue. Characteristic changes of the aging eye Rones, (1938) asserted that senile alterations in some ocular tissues were manifested by alterations in function, in others by visible degenerative disturbances, and at times senile variations were seen only by microscopic examination of the ocular tissues. In general, Friedenwald (1952) summarized the senile changes of the eye as consisting of an increase ia the density of the ocular tissues with age. Friedenwald characterized the increased density as being due to loss of water, increased interstitial fibrillar tissue, loss of fat and elasticity, and an accumulation of various inert materials within the densified tissue.
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