الفهرس 
Introduction & Aim of the workOnly 14 pages are availabe for public view
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Abstract
Summary
The human eye is one of the most complex parts of the body. The cornea is a tissue in the human eye that has the purpose of improving the quality of the image formed in the retina. It is a convex, transparent, intensely innervated and sensitive membrane located in the anterior portion of the eyeball.
The cornea acts as clear and one of the transparent tissues in the human body with thickness that is approximately 0.52 mm centrally and 0.65 mm peripherally and its average horizontal diameter is about 12 mm. It has no blood vessels to nourish it, but it obtains its nourishments from the tear and aqueous humor. It is an organized group of cells and proteins arranged in five layers.
Dry eye syndrome is a disease of cornea, the ocular surface and tear film that is prevalent in older adults. Even though the minimal degree of visual acuity loss in dry eye patients which occurring in the aging population this minimal change in visual status can lead to a significant decrease in visual function and quality of life.
Aging is a biological phenomenon that involves an increase of oxidative stress associated with gradual degradation of the structure and function of the cornea. Age-related changes in the cornea and ocular surface tissues have a major effect on vision. More severe age-related disease can cause loss of transparency and then blindness.
Ascorbic acid has been shown to have protective effects in the repair of many corneal diseases in animals and in humans, such as in UV irradiation, chemical corneal burns, corneal neovascularization and inflammation. However, few reviewed study literatures studied the protective role on age related changes on the cornea.
The aim of this work was to evaluate the histological and ultra-structural changes induced by aging on the cornea of albino rat and the possible protective role of vitamin C.
Fifty adult male albino rats were enrolled in this study and divided as follows:
group I: (n = 10 rats, 6 months old); rats received no medications.
group II: (n = 20 rats, 18 months old); rats divided into two subgroups: (10 rats each).
Subgroup A: rats received no medications.
Subgroup B: rats received vitamin C orally once daily (200 mg/kg body weight) for 36 days.
group III: (n = 20 rats, above 24 months old); rats divided into: subgroups: (10 rats each).
Subgroup A: rats received no medications.
Subgroup B: rats received vitamin C orally once daily (200 mg/kg body weight) for 36 days.
All rats were anesthetized by light chloroform anesthesia, given by inhalation. Then, rats were sacrificed by decapitation. The two eyes were enucleated.
The corneas were extracted by circumferential excision 2mm posterior to the corneoscleral junction; one cornea was used for light microscopic examination and the other cornea was used for electron microscopic examination.
Results revealed that:
In the current study aging of the cornea was studied histologically by examining corneas of albino rats of different age groups: 6 months, 18 months and above 24 months. Moreover, the protective effect of vitamin c on aging of cornea was examined in two different ages 18 months and above 24 months. The corneas of one eye were stained by haematoxylin and eosin stain, Masson’s Trichrome stain and Immuno-histochemical study (caspase-3), and were histologically examined using light microscopy, while the other eyes’ corneas were used for ultra-structural examination using Transmission Electron microscopy.
The cornea of 6 months aged rats was considered as control groups, it consists of 5 layers: stratified squamous corneal epithelium, Bowman’s membrane, stroma, Descemet’s membrane, and endothelium.
Aging 18 months aged rats, was associated with irregular corneal surface with apparent keratinization of the corneal epithelium as well degenerated corneal epithelial cells with absent nuclei. Moreover, separation of corneal stroma from bowman’s membrane, and reduced number of keratocytes in corneal stroma were observed, with moderate caspase3 immuno-reactivity, above 24 months aged rats, was associated with significant separation of collagen bundles, disorganized corneal stroma and cytoplasmic vacuolation with small dark nuclei of corneal epithelial cells with strong positive caspase-3 immuno-reactivity. Which was in contrast to that observed in 6 months aged rats where the cornea showed normal histological architecture with no signs of atrophy with negative caspase-3 immuno-reactivity.
The results of current study showed that the area percent of caspase3 immuno-reactivity was statistically high significant in 6 months aged corneal rats which had the lowest area percent of caspase3 immuno-reactivity, when compared to 18 months above 24 months aged corneal rats. In addition, there was no significant difference between 18 months aged corneal rats and above 24 months aged corneal rats.
There was significant protection of vitamin C on the signs of aging in18 months aged corneal rats as detected with mild positive caspase-3 reaction which indicate apoptosis but showed mild protection on above 24 months aged groups. This was more confirmed by the morphometric measurement of area percentage of caspase 3 immunoreactivity that was statistically high significant in 18 months aged corneal rats and statistically significant in above 24 months aged corneal rats.
The results of current study showed that the epithelial height of corneal epithelium was statistically high significant in 6 months aged corneal rats which had the highest epithelial height, when compared to above 24 months aged corneal rats. In addition, 18 months aged corneal rats were statistically significant increase than above 24 months aged corneal rats.
The results of current study showed that treatment with vitamin c improved the thickness of cornel epithelium and decrease cellular loses in corneal endothelium in all treated groups. This was more confirmed by the morphometric measurement of epithelial height of corneal epithelium that was statistically high significant in 18 months aged corneal rats and non-significant in above 24 months aged corneal rats.
In conclusion, aging affects the cornea of albino rats, and vitamin C may have a protective effect on aging of cornea.