Evaluation of the Developmental Morphology of the Eyeball of the Red Sokoto Goat (capra hircus)

Evaluation of the Developmental Morphology of the Eyeball of the Red Sokoto Goat (capra hircus).

ABSTRACT

This study traced the developmental histology of  the eyeball of the Red  Sokoto goat during  the prenatal and postnatal stages.

Thirty Red Sokoto goat fetuses, 10 neonatal and 10 adult goat heads obtained  from  the  abattoir were used for this study. The fetuses were aged using the  standard  formula  while those of the adult goats were estimated by dentition. The eyes were dissected  from the  head and assigned to five groups (A-E). Eye samples were routinely processed for histological studies.

Sections were examined with a light microscope and photographed with a Moticam digital camera attached to a microscope. Corneal thickness was measured  in all groups and  data obtained were analysed using analysis of variance. Variant means were separated  using  the least significant method (LSD) and significant difference  was  accepted  at  probability  level (p < 0.05).

The corneal primordium was present in the eyes of fetuses in group A. The anterior and posterior epithelia were of the simple cuboidal type. The  corneal  epithelium  became  bilayered while the primordium of the limbus and the sclera appeared. In group B, the Descemet’s membrane was visible. All the layers of the sclera except the lamina fusca were fully differentiated.

The differentiating lamina cribrosa appeared at this stage. In group C, the Bowman’s layer was observed. The limbus, lamina cribrosa and  sclera  were  well differentiated with the entire scleral layers present. In group D, the corneal epithelium  had  more cellular layers and pigments were observed in limbus. In group  E,  the  corneal  epithelium was of the non keratinized stratified squamous type.

The Descemet’s membrane  was thick. Apart from the cornea, all other regions of the fibrous coat had more melanocytes and  pigments in group  E.

The central and peripheral corneal thicknesses of the adults  (242.29± 23.95; 179.34 ± 8.37) were significantly higher (p < 0.05) than those of the fetuses of 2nd (68.50 ± 7.14; 71.20 ± 6.93), 3rd (90.47 ± 8.85; 68.35 ± 4.73) and 4th (81.71 ± 14.11; 88.87 ±15.26) months of gestation and also that of the neonate (91.61 ± 15.81; 90.99 ± 9.08).

In the eyes of group A, the iris was present as well as the iridopupilary membrane. The annular sinusoid was also present, choroidal differentiation was also initiated. Also pigment cells appeared in the stroma of the iris along with the dilator pupilary muscle myocytes. The ciliary body appeared as ciliary folds covered by a bilayered epithelium.

The formation of the trabecular meshwork had been initiated while the iridocorneal angle was still closed. The angular  aqueous  plexus  was  seen  at  this stage.  The  choroid  also  started  differentiating. In group B, the constrictor pupillary muscle had  appeared  while  the  iridopupillary membrane had started regressing.

The granula iridica also had started forming and the pectinate ligament appeared. The formation of the tapetum fibrosum was initiated at this stage. In group C, the ciliary folds formed the ciliary processes. The iridocorneal angle opened at this stage with the dorsal angle opening before the ventral one.

In group D, the iridopupilary membrane had  broken down and the anterior iridal surface was thrown into folds. The ciliary cleft was also formed at this stage. In group E, the crypts of Fuschs were seen on the anterior iridal surface. Few radially and circularly oriented muscle fibers were also seen in the ciliary body and the suprachoroidal space also appeared.

The retinal primordium was present in the eyes  of group  A as well as the commencement of differentiation into retinal layers and  cell  types.  The retinal cell types and layers appeared in the eyes of group B. The physiologic cup appeared in the eyes of group C at the optic nerve head. In group E, the rows of cells in the outer nuclear layer and inner nuclear layer of the retina were fewer than those in group D.

Glial cells were seen at the optic nerve head at this stage. In group A, the lens capsule was present. The lens epithelium was of the pseudostratified and simple columnar types centrally and equatorially respectively. This changed to simple cuboidal and simple columnar centrally and  equatorially in groups C and D.

In group E, the lens epithelium was made up of simple cuboidal type centrally and simple columnar type at the equator. Hyaloid vessels were present in group A, became smaller and sparse in group C, few were seen on the posterior surface of the lens and equator in group D and they were absent in group E.

The development of the nervous and  vascular  layers  progressed  posterior-anteriorly  while that of the fibrous layer progressed anterior-posteriorly. Also the  pigmentation  of  the  different parts of the eye increased with fetal growth and was highest in the adult.

This study has shown that by late 3^rd trimester, the RSG eyeball has acquired a full complement of the nervous, vascular and fibrous layers along with other structures necessary  for  vision.

Therefore it essentially had the same morphology as in the adult and appeared capable of carrying out the function ascribed to the eyeball in the adult.

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TABLE OF CONTENTS

TITLE PAGE——— i

CERTIFICATION——– ii

DEDICATION—— iii

ACKNOWLEDGEMENT————- iv

TABLE OF CONTENTS—— v

SUMMARY——– xi

CHAPTER ONE

• INTRODUCTION……………. 1
• STATEMENT OF PROBLEM…….. 2
• MAIN RESEARCH OBJECTIVE…………. 3
• SPECIFIC OBJECTIVES……… 3

CHAPTER TWO LITERATURE REVIEW

• EMBRYOLOGY OF THE EYEBALL………….. 4
  • Development of the cornea…………………. 5
  • Development of the sclera……………….. 6
  • Development of the choroid………….. 6
  • Development of the iris and ciliary body……….. 6
  • Development of the lens……………. 7
  • Development of the retina………………… 7
  • Development of the optic nerve……………………………. 8
• GROSS ANATOMY OF THE EYEBALL……………….. 8
  • OUTER FIBROUS TUNIC…………………….. 10
    • Cornea 10
    • Sclera 11
  • MIDDLE VASCULAR TUNIC………….. 12
    • Iris 13
    • Ciliary body…………. 14
    • Choroid 16
  • INNER NERVOUS LAYER……. 17
    • Retina 17
  • OPTIC NERVE……….. 18
  • LENS 18
• HISTOLOGY OF THE EYEBALL…………. 19
  • OUTER FIBROUS TUNIC……………. 19
    • Cornea 19
    • Sclera 21
  • VASCULAR LAYER……. 22
    • Iris 23
    • Ciliary body………….. 24
    • Choroid 25
    • Tapetum lucidum…………. 26
    • Choriocapillaris………… 27
  • NERVOUS TUNIC…………………………………….. 28
  • Retina 28
    • Retinal Pigment Epithelium (RPE)………………… 28
    • Layer of rods and cones………………… 29
    • External Limiting Membrane………… 30
    • Outer Nuclear Layer………………….. 30
    • Outer Plexiform Layer………….. 30
    • Inner Nuclear Layer…………… 31
    • Inner Plexiform Layer……………… 33
    • Ganglion Cell Layer……………… 33
    • Nerve Fiber Layer……….. 34
    • Inner Limiting Membrane…………….. 34
    • Optic Nerve 34
    • LENS 34

CHAPTER THREE MATERIALS AND METHODS

• ACQUISITION OF SPECIMEN………………….. 37
• AGEING 37
• TISSUE PREPARATION………………… 37
• PHOTOMICROGRAPHY……….. 38
• HISTOMORPHOMETERY………………… 38
• STATISTICS………….. 38

CHAPTER FOUR RESULTS

• FETUSES OF ABOUT 45 DAYS………………. 39
  • FIBROUS TUNIC…………… 39
    • Cornea 39
  • VASCULAR TUNIC…………… 39
    • Iris 39
    • Choroid 40
  • NERVOUS TUNIC. 40
    • Retina 40
  • LENS 41
• FETUSES OF ABOUT 59 DAYS…………………… 42
  • FIBROUS TUNIC…………………… 42
    • Cornea 42
    • Sclera 42
  • VASCULAR TUNIC………… 43
    • Iris 43
    • Ciliary body…. 43
    • Choroid 44
  • NERVOUS TUNIC……… 45
    • Retina 45
  • OPTIC NERVE……………….. 45
  • LENS 45
• FETUSES OF ABOUT 75 DAYS………. 46
  • FIBROUS TUNIC……………………… 46
    • Cornea 46
    • Lamina cribrosa…………. 47
  • VASCULAR TUNIC………. 47
    • Iris 47
    • Ciliary body……………. 47
    • Choroid 48
  • NERVOUS TUNIC…… 48
    • Retina 48
  • THE LENS 49
• FETUSES OF ABOUT 105 DAYS……………………… 49
  • FIBROUS TUNIC………………… 49
    • Cornea 49
    • Sclera 50
  • VASCULAR TUNIC………………. 50
    • Iris 50
    • Ciliary body………. 51
    • Choroid 52
  • NERVOUS TUNIC………………. 52
    • Retina 52
  • OPTIC NERVE…………………… 53
  • LENS 53
• NEONATE……………… 54
  • FIBROUS TUNIC…………. 54
    • Cornea 54
    • Limbus 55
    • Sclera 55
    • Lamina cribrosa………………… 55
  • VASCULAR TUNIC……… 56
    • Iris 56
    • Ciliary body………………… 57
    • Choroid 57
  • NERVOUS TUNIC……….. 58
    • Retina 58
  • OPTIC NERVE………….. 61
  • LENS 61
• ADULT…….. 62
  • FIBROUS TUNIC………….. 62
    • Cornea 62
    • Limbus 63
    • Sclera 63
    • Lamina cribrosa………. 64
  • VASCULAR TUNIC…………………. 64
    • Iris 64
    • Ciliary body….. 65
    • Choroid 67
  • NERVOUS TUNIC………………………. 67
    • Retina 67
  • OPTIC NERVE HEAD……………. 70
  • LENS 71

FIGURES……

• OUTER FIBROUS LAYER……. 144
  • Cornea 144
  • Sclera 148
  • Lamina Cribrosa…………………… 148
• MIDDLE VASCULAR COAT………………. 149
  • Iris 149
  • Ciliary Body………….. 151
  • Choroid 154
• INNER NERVOUS COAT…………………………….. 157
• LENS 163

REFERENCES 167

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INTRODUCTION

Veterinary ophthalmology is a recognized discipline of veterinary medicine. Ocular examination is important in most clinical examinations and the understanding and  diagnosis   of ocular disorders rely on knowledge of normal ocular structure and physiology.

The eye of vertebrates is a highly specialized extension of the brain with a camera-like arrangement that provides sensitivity to light, good  visual acuity and a wide field of vision.

It  is a complex and highly developed photosensitive organ that  permits an accurate analysis of  the form, light intensity and colour reflected from  objects  (Junqueira  and  Caneiro,  2005).

The eye is a composite collection of tissues with similarities to the morphology and functions  of tissues found in most other systems; therefore it provides a good opportunity for the examination of different tissue types without.

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REFERENCES

Aguirre, G., Rubin, L., Bistner, S. 1972. Development of the canine eye. American Journal of Veterinary Research. 33: 2399-2414.

Ahnelt, P.K., Kolb, H. 2000. The mammalian photoreceptor mosaic-adaptive design. Progress in Retinal and Eye Research 19:711-777.

Almubrad, T., Khan, M.F.J., Akhtar, S. 2010. Swelling studies of camel and bovine corneal stroma. Clinical Ophthalmology 4:1053-1060.

Anderson, B. 1968 Ocular effects of changes in oxygen and  carbon tension.  Transactions of the American Ophthalmological Society 66:423-474.

Arnott, H.J., Maciolek, N. J., Nicol, J.A. 1970. Retinal tapetum lucidum: a novel reflecting system in the eye of Teleosts. Science. 169:478-480.