الفهرس | Only 14 pages are availabe for public view |
Abstract The dromedary camel is one of the most important domestic animals in the arid and semi arid regions. Compared to other livestock, the dromedary camel is unique for having an exceptional ability to survive and thrive under adverse climatic conditions such as high ambient temperatures, low rainfall and scarcity of feed, unbearable solar radiation and water scarcity, therefore, it offers an ideal animal for animal production in arid and semi arid regions of the world. The eye of the camel plays an important role in its survival in these arid zones. This study was initiated to detail the major landmarks and the time course of the prenatal development of the eye tunics in the dromedary camel; to analyze the dromedary camel’s visual world through assessment the total number and topographic distribution of retinal ganglion cells; and to survey the normal findings of ocular structures as displayed in Ultrasonography (US), Computed Tomography (CT), and Magnetic Resonance Imaging (MRI). Firstly, Serial histological sections of dromedary camel embryos and fetuses were used for prenatal development of the eye tunics; age estimation was made on the basis of gestational size, crown vertebral-rump length (CVRL), which ranged from 1.2 cm to 110 cm. The eye of the dromedary camel developed in a similar manner to that of the human and domestic animals eyes; the principal differences were in the time of occurrence of certain developmental events, pigmented peripheral cornea near the limbus, a remarkably thickened Descemet’s membrane and pigmentation in the corneo-scleral junction, which represent an adaptive modification in relation to a severe environment. Secondly, Left eyes from 24 adult camels, 3-4 years old, were used for whole-mounts and retinal collodion parasagital sections (confirmatory method). Furthermore, the visual acuity histologically was estimated. The dromedary camel has about 407,000 RGCs. The topographic distribution of RGCs showed a well defined horizontal visual streak with a dorsotemporal extension of higher cell density. The peak visual acuity in the dromedary camel was 13.52 cycles/degree. Artiodactyls take always precautions against predators. Therefore, the retina in artiodactyls has a visual streak for a horizontal wide visual field. Thus, the visual streak found in the dromedary camel is formed by common needs among artiodactyls. Thirdly, six fetuses of five CVRL stages; 33.5, 54.5, 71, 74 and 84 cm and six adult fixed eyeballs were used for comparative imaging. Complementary cross-sectional imaging modalities of the eye: Ultrasonography (US), Computed Tomography (CT), and Magnetic Resonance Imaging (MRI) were applied. |