This new edition of the Handbook of Visual Optics, Volume One, provides an authoritative and up-to-date overview of physiological optics. It spans the field from the physical foundations of light propagation in the eye to the biological and perceptual mechanisms underlying human vision. Building on the success of the first edition, this volume has been updated and expanded to reflect major advances in understanding the optical properties of the eye, visual performance, and fundamental measurement methods. Integrating perspectives from physics, biology, medicine, psychology, and engineering, the chapters cover the geometry and wave optics of the eye, its anatomy and function, the behavior of optical aberrations and scattering, and the neural processes that shape perception. This first volume establishes the essential basis for the companion Volume Two, which addresses ophthalmic instrumentation and applications.