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Abstract
Summary and conclusion
With the recently detected ozone hole, some areas of the world receive more UV-B than they did earlier. In addition, many clinical experiences and evidence from experimental studies show that UV-B is absorbed by the lens of the eye and can cause damage to this tissue, including cataract. Ultraviolet radiation from the sun light is commonly divided into three component according to the wave length: UV-C (100-280 nm), UV-B (280- 315 nm) and UV-A (315- 400nm).
It has been suggested that the effects of UVB exposure differ between acute high-dose and chronic low-dose exposures. A few studies have been made on the effects of UVR on the cornea and lens compared to the studies made on the skin were the epidermis is also ectodermal in origin.
So, the present study was conducted to evaluate the effects of UV-B radiation on the lens and cornea in albino rats in different ages and time of exposure..
The study wad done on 5 groups, according to the age , 20 rats for each ( totally 100 rats): control group (c), Exposed (E1) group 3 weeks age, Exposed (E2) group 6 weeks age , Exposed (E3) group 10 weeks age, and Exposed (E4) group 18 weeks age. Four age groups, aged 3,6,10 &18 weeks (20 rats for each) were irradiated by UV-B with wave length 300nm and intensity of 8kj/m2. Each group was divided into two subgroups (A &B) according to the time of exposure to the UV-B radiation 15 and 30 minutes. The control group (c) were divided into 5 rat for each age group.
Before UV exposure Tropicamide (mydriacyle) will be instilled in both eyes for10 minutes to minimize the possible variation in the pupil sizes during the exposure. the rats will be anesthetized with 2.5 mg/kg ketamine intrperitoneally. One week after the exposure (for each group), rats were killed with an over dose of ethier. Both lenses were extracted under the surgical dissecting microscope. Half of the lenses were kept in balance salt solution (BSS). The other half were fixed in 2.5% Glutaraldehyde followed by formalin for histological specimen. The isolated lenses in BSS were photographed against a dark background with a white grid and descriped the morphologic changes in the exposed lenses and evaluated to identify the different pattern of cataract in these lenses.
Histological specimen of the exposed and non-exposed rat lenses for the light were done to evaluate the microscopic changes in the lens and were stained with H&E and observed under light microscope. Two corneas from each group were fixed in 10% formalin stained with Hematoxylin and eosin (H&E) staining and periodic acid-Schiff (PAS). Lenses were also investigated by the spectrophotometer. The resulting absorption spectra helped in recognizing the cataract if present and also its different stages.
This study demonsterate that, UV-B has powerful effects on the rat lens and development of different types of cataract (early cortical, cortical equatorial, sutural, early nuclear, and nuclear) which, differs according to the age and time of exposure. The more exposure to UV-B, the more the cataract develops.
In the present study, Histological analysis with Hematoxylin and Eosin (H&E) of the lens showed that, UV-B induced disturbance in the lens fibers. Swollen fibers, vacuolar structures and disturbed order of the fibers as compared with the regular order and equal size of fibers in the control lenses in all age groups. Corneal epithelium was affected in the form of the degenerated epithelial cells (changes in size, density, the nuclei were not stained homogenously, intracellular edema, pyknosis, and fragmented nuclei ). Epithelial hyperplasia, thinning, and also loss of the epithelial continuity (erosion), irregularity of Bowmen’s membrane, stromal edema, disturbed collagenous fibers arrangement in the stroma with total loss of keratocytes and appearance of stromal blood vessels.