Comparative Morphometric Study of the Optic Nerve in One-Humped Camel (Camelus dromedarius) and Donkey (Equus asinus)

Abstract

Comparative anatomical studies were made measuring several morphological characteristics seen in cross-sections of the optic nerve of one-humped camel (Camelus dromedarius) and donkey (Equus asinus). Six optic nerves from each animal were used in this study. The optic nerve samples were obtained about 5mm behind the eye. The axon numbers and diameters were studied with light and transmission electron microscopes. Axon diameters were measured in samples of 500 axons taken from several locations in a cross section of the optic nerve behind the eye. The total cross-sectional area of the optic nerve was about 35% smaller in the donkey than in the camel. The fibers are organized in fascicles. The fiber density and number was 2.3 times higher in the camel than in the donkey. The total number of optic nerve fibers counted was 1173323 ± 33039 in camels and 495754 ± 10126 in donkeys. The majority of axons were myelinated in the optic nerve of both animals. There was a significant regional variation in the size of optic nerve axons. Large myelinated axons were observed in the dorsal and ventral periphery, whereas smaller myelinated fibers and a high proportion of unmyelinated fibers were found in the center of the nerve.