Through the lens clearly: phylogeny and development: the Proctor lecture.

The adaptive radiation of the eye from an optical perspective has long intrigued scientists, at least from the 19th century. In a paper on the optics of the fish lens published in 1816, David Brewster, the Scottish scientist, wrote, “There is, perhaps, no subject in natural history which has excited so much attention, as the structure and functions of the eyes of animals; . . . and the natural philosopher, considering it as the work of infinite intelligence, ardently anticipated the improvement of optical instruments from the imitation of this perfect model.” Thus, Brewster refers to the fundamental interest in the natural history of the eye as well as the potential benefits, or applications, this interest can lead to. A little later, in the 20th century, August Krogh, the Danish physiologist and Nobel laureate, wrote in regard to the value of comparative animal research in general that “for almost every physiological problem there is an animal on which it can be best studied.” Two examples that come to mind include the use of the giant squid axon by Hodgkin and Huxley to clarify the mechanism of neuronal impulse conduction and the study of the neural response of the compound eye of Limulus (the horseshoe crab), to examine the process of lateral inhibition. Additional examples will be highlighted in the review that follows. The optical characteristics of the eye have been and continue to be a focus of comparative interest, and nobody has done more to draw attention to the optical solutions that have evolved among vertebrates than Gordon Walls in his opus titled The Vertebrate Eye and its Adaptive Radiation. The fascination with the study of the varied optical elements of the eye, generally the structure and function of the cornea and lens and the mechanism of accommodation, stems in large measure from interest in how living biological tissue can operate in a physical sense to produce retinal images of good quality.