Chapter 10 - Color Vision and Night Vision

Day vision and night vision are two separate modes of visual perception and the visual system shifts from one mode to the other based on ambient light levels. Each mode is primarily mediated by one of two photoreceptor classes in the retina, i.e., cones and rods. In day vision, visual perception is primarily cone-mediated and perceptions are chromatic. In other words, color vision is present in the light levels of daytime. In night vision, visual perception is rod-mediated and perceptions are principally achromatic. Under dim illuminations, there is no obvious color vision and visual perceptions are graded variations of light and dark. Historically, color vision has been studied as the salient feature of day vision and there has been emphasis on analysis of cone activities in color vision. Night vision has historically been studied in terms of rod activity and considerations of the shift from day vision to night vision. This chapter will review basic aspects of rods and cones and neural pathways that process rod and cone information. Measurement of sensitivity during dark adaptation is discussed as the established measure of the shift between day vision (cone vision) and night vision (rod vision). Clinical assessment of rod and cone sensitivities using dark adaptation function as a means of assessing retinal disease is also discussed. Color vision is discussed in terms of experimental paradigms and theoretical considerations and variations in human color vision are described. Evaluation of color vision can be helpful in understanding the underlying mechanisms of some retinal diseases and suggestions for clinical evaluation of color vision are offered. In the last section of this chapter, new developments in color vision research are discussed. Color Vision and Night Vision Dingcai Cao