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Chapter 21:
Quality of the Human Visual System
With the comments and remarks provided in the last chapter, the foundation and characterization of the CAGE-Barten model can be considered completed. There remain two issues to be discussed: the chance of improvement for human vision, and the structure of spatial visual channels. These issues are discussed in this and the following chapter. This chapter is devoted to speculations on the overall quality of the human visual system. Chapter 12 discussed the performances of the human eye as represented by the CAGE eye model from a purely optical perspective. One result obtained in those pages was that the optical design of the human eye represents an intermediate step between a rough optical system (with all spherical surfaces) and a diffraction-limited system, free of spherical aberration. The eye was shown to be the result of a not fully optimized optical design that employed trichromatic photoreceptors because of the enormous advantage of color vision over monochromatic vision. It was further pointed out that the refractive media of the eye are characterized by a poor capability of chromatic dispersion compensation. The resulting compromise did not provide an evolutionary gain for a stronger reduction of third-order aberrations of the eye. The discussion in Chapter 12 can now be completed with the estimates of visual performance, thus providing more convenient means to evaluate the actual ocular design in relation to other potential solutions. This includes not only the optical portion of the design, but also the neural portion, in an effort to provide answers to the basic question: could evolution have produced a better eye design?
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