Publisher Summary The only known function of the eye is to facilitate the unfettered transmission of light from the external environment to the photoreceptors of the retina and from there on to the visual cortex where the signals are translated into images. Although the eye is only a few centimeters in diameter, it is an enormously complex organ that is composed of a multitude of tissues and cells, many of which are found nowhere else in the body. This remarkable organ is an extension of the brain, and, like the brain, has limited regenerative properties. Two of the crucial components of the eye that are necessary for normal vision—the corneal endothelium and the photoreceptor layer of the retina—are incapable of regeneration. Accordingly, traumatic events, such as inflammation, can inflict irreparable damage to these tissues, resulting in blindness. Yet, the consequences of ocular infection with microbial pathogens could be equally threatening to the visual apparatus and the host. The immune response to ocular antigens must be a measured one that balances protective immunity to pathogens with the potential injury to innocent bystander ocular cells that cannot regenerate. Thus, the nature of the ocular immune response is an expression of this compromise.