STUDY ON AGEING CHANGES IN THE CORNEA AND RETINA OF BUFFALOES (Bubalus bubalis)
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Date
2019-08
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SRI VENKATESWARA VETERINARY UNIVERSITY TIRUPATI - 517502. (A.P.) INDIA
Abstract
The present study was conducted on age related changes in the cornea and
retina of buffaloes. A total of 63 samples from three age groups of buffaloes
irrespective of their sex were used in this study.
The corneal epithelium of buffaloes was nonkeratinized stratified
squamous epithelium with 6 to 7 layers at early age and 12-14 layers of cells in
adult animals. There were three types of cells noted in the cornea without any
distinct boundaries viz., basal cells, intermediate or wing cells and superficial
cells. The Bowman’s membrane was a homogenous and acellular layer and its
thickness was increased with advancement of age. The stroma of cornea
consisted of uniform collagen fibrils and they were loosely arranged in young
animals and tightly packed in aged animals. The keratocytes were interposed
between the collagen fibers, which were elongated and thick in young animals
and thin in old animals. The Descemet’s membrane was a homogenous non
cellular fibrous band with dark anterior band zone and light posterior band zone.
The corneal endothelial cells were small and firmly adherent to each other in
young buffaloes, but they were enlarged and increased in size in old buffaloes.
The age related pigmentation was noticed in epithelium and stroma in aged
animals. Numerous sub basal nerve plexuses observed in stroma i.e. between the
basal cells, wing cells and superficial cells in all age group of animals. All layers
of cornea showed moderate to strong reaction for neutral and acid
mucopolysaccharides in buffaloes. In scanning electron microscopy study, no apical microvilli on superficial epithelial cells were noted. The Bowman’s layer was consisted of anterior clear zone lamina lucida and posterior dense zone lamina densa.
The immunohistochemical reactivity of cytokeratin 3 was noted in the
basal cells of corneal epithelium. The reactivity of CD 31 was increased with age
in corneal endothelial cells. In the peripheral portion of retina the retinal pigment epithelium was cuboidal and they were packed with melanin pigment. The thickness of RPE was increased and quantity of melanin pigment was decreased with age advancement. In the photoreceptor layer two types of cells were noted i.e. rod and cone cells. They were tightly packed in young age, whereas loosely arranged in older
animals. The number of cones progressively increased in number with
advancement of age. The nuclei of outer nuclear layer were displaced into outer
plexiform layer in the retina of old animals. The outer limiting membrane was
continuous throughout the life in the present study. The thickness of outer
plexiform layer was increased with advancement of age due to enhancement of
synaptic fibers density. The number and density of horizontal, bipolar and
amacrine cells were decreased from young to old buffaloes. The thickness of
inner plexiform layer was increased with advancement of age due to increased
cystoid spaces and thickening of retinal blood vessels between the synaptic fibers
of bipolar, amacrine and ganglion cells. The large α and small β ganglion cells
were observed in the retina of buffaloes. The number of α ganglion cells were
progressively increased with advancement of age. The corpora amylacea and
thickened blood vessels were observed in the nerve fiber layer of retina of old
buffaloes. The inner limiting membrane was loose and interrupted in young
animals whereas, thick and uninterrupted in old buffaloes.
The total thickness of retina was decreased form young to adult animals in
the present study. The increased number of cone cells, formation of cystoids
spaces in the inner plexiform layer, increased size of ganglion cells, hyalinization
and thickening of blood vessels in inner plexiform and nerve fiber layers were
noticed with advancement of age in buffaloes. In the present study SEM revealed that RPE were tightly packed with rod to spherical and elongated melanin pigment granules in young animals and loosely packed in old buffaloes. Numerous capillaries were observed in the inner nuclear layer. Numerous cystoid spaces were also observed in outer plexiform and nerve fiber layers of retina in old animals.
Immunohistochemical studies revealed that PAX6 activity on RPE was
decreased with advancement of age in buffaloes. The activity of recoverin on
photoreceptor cells and their nuclei and binucleate cells of retina was decreased
in old animals. The activity of calbindin was strong to moderate in horizontal and
amacrine cells and it’s activity decreased with advancement of age in buffaloes.
Retina macula was appeared as strip like and pale in color located dorsal
to the optic disc in buffaloes. In the present study macula contained large RPE
cells with tightly packed melanin pigment, relatively more number of cone cells,
cells of inner nuclear and less cystoid degeneration in inner plexiform and nerve
fiber layers was observed when compared to peripheral retina. Further, there was
less degenerating changes in the macula when compared to peripheral retina with
advancement of age in buffaloes. The ora serrata was a nonsensory portion of the retina which includes pars ciliaris retina and pars iridica retina that cover ciliary body and iris. This region consisted of less number of rod cells, more number of horizontal and amacrine cells and few large ganglion cells were observed when compared to the
peripheral retina in the present study. Optic disc was round to oval in shape and in this all retinal layers were gradually disappeared near the optic disc. At the junction of pars optica retina and optic disc RPE cells were small and devoid of melanin pigment. The blood vessels were large near optic papilla and they were small and tiny away from the papilla in buffaloes.
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