The Avian Eye and its Adaptations

The avian eye is considered to be “supreme amongst all living creatures” and capable of attaining “an order of excellence unmatched in any other species not excepting man” (Duke-Elder, 1958). Many structural and functional adaptations have become involved in the perfection of visual processes in birds which, according to Pumphrey (1948a) represent the culmination of phylogenetic development toward diurnal vision. This chapter is concerned with several of these adaptations, the most obvious of which are the oil droplet inclusions and glycogen deposits within their photoreceptors, the well-developed areae and foveae within their retina and the highly vascularized pecten within their vitreous body. A detailed description of the avian eye is not intended; excellent sources are available on this subject: Wood (1914), Slonaker (1918), Franz (1934), Walls (1942), Rochon-Duvigneaud (1943), Polyak (1957), Duke-Elder (1958), and Hodges (1974)