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Objective Diurnal birds of prey (raptors) are considered the group of animals with highest visual acuity (VA). The purpose of this work is to review all the information recently published about the visual system of this group of animals. Material and methods A bibliographic search was performed in PubMed. The algorithm used was (raptor OR falcon OR kestrel OR hawk OR eagle) AND (vision OR “visual acuity” OR eye OR macula OR retina OR fovea OR “nictitating membrane” OR “chromatic vision” OR ultraviolet). The search was restricted to the “Title” and “Abstract” fields, and to non-human species, without time restriction. Results The proposed algorithm located 97 articles. Conclusions Birds of prey are endowed with the highest VA of the animal kingdom. However most of the works study one individual or a small group of individuals, and the methodology is heterogeneous. The most studied bird is the Peregrine falcon (Falco peregrinus), with an estimated VA of 140 cycles/degree. Some eagles are endowed with similar VA. The tubular shape of the eye, the large pupil, and a high density of photoreceptors make this extraordinary VA possible. In some species, histology and optic coherence tomography demonstrate the presence of 2 foveas. The nasal fovea (deep fovea) has higher VA. Nevertheless, the exact function of each fovea is unknown. The vitreous contained in the deep fovea could behave as a third lens, adding some magnification to the optic system. pre-print 778 KB

Objective To communicate relevant and striking aspects about the visual system of some close invertebrates. Material and methods Review of the related literature. Results The capacity of snails to regenerate a complete eye, the benefit of the oval shape of the compound eye of many flying insects as a way of stabilizing the image during flight, the potential advantages related to the extreme refractive error that characterizes the ocelli of many insects, as well as the ability to detect polarized light as a navigation system, are some of the surprising capabilities present in the small invertebrate eyes that are described in this work. Conclusions The invertebrate eyes have capabilities and sensorial modalities that are not present in the human eye. The study of the eyes of these animals can help us to improve our understanding of our visual system, and inspire the development of optical devices.