ABSTRACT
This chapter identifies some important differences among common laboratory animals. The eye itself can be divided into three concentric tunics plus the internal components. The three tunics from the outside surface of the eye inward are the fibrous tunic, the vascular tunic, and the neuroectodermal tunic. The mammalian cornea is a transparent, avascular structure that functions to transmit and refract light, and as a protective barrier for the internal ocular contents. The eye and adnexa are very similar in all mammals; however, some ocular anatomical and physiological differences are important to recognize when selecting animal models to test drugs, cosmetics, dentifrices, shampoos, and other compounds intended for human use. The cilia are found external to the ducts of the tarsal glands and are usually more plentiful and longest in the upper lid. Cilia are absent on the lower eyelid of the dog and horse and are absent altogether in the cat.
