These neurons have a characteristic distribution in the ten distinct layers of the retina, and have interconnections via two different pathways, namely, the vertical and horizontal pathways. These neuron types are the photoreceptors, bipolar cells, ganglion cells, horizontal cells and amacrine cells. The human retina is a complex mosaic ( Figure 2B,C) comprised of five classes of neurons specialised in processing the visual information received by the eye. D, dorsal N, nasal T, temporal V, ventral. ( Right) example of a typical habitat of the mouse (ground) and its retina RGC density distribution. ( Center) example of a typical habitat of the hawk (sky) and its retina RGC density distribution. ( Left) Habitat of simians (jungle) and the RGC density distribution in the human retina. Snapshots of the habitat of different species along with their representative RGC density distribution across their retinal surfaces. This retinal organization and associated visual behavior had significant consequences for the evolutionary development of the occipital, frontal and prefrontal cortical areas in the simian lineage, as vision became the most important sensory system. Due to this retinal configuration with a central zone of higher visual acuity extending over a limited field of view, humans and other higher primates have developed highly motile eyes. Nasally to the macula is located the optic disc in this zone, all ganglion cell axons converge to exit the eye en route to the visual brain via the retinofugal pathways. At the macular center is located the fovea, a zone with a 700 µm deep focus approximately 1.5 mm in diameter, composed exclusively of cones, thus providing the highest resolution for daytime vision. This area (5.5 mm in diameter) is specialized for color and detailed vision enabled by its higher density of cones and ganglion cells. Humans and other primates need to identify food and predators against cluttered environments, and consequently evolved a zone of acute vision located at the center of the retina, namely, the macula. However, the layout of the retina varies between species to meet their specific needs, behaviors, and habitat ( Figure 1). The retina has a complex laminar organization and a cellular composition that are similar in all vertebrates. It is a laminar tissue containing neurons and glial cells that plays the crucial role of phototransduction, the process of converting light energy into encoded neural signals delivered to the brain. The mammalian eye is composed of three concentric and distinct layers of tissue: the sclera, the uvea, and the retina. The eyes have adapted to complex environments, enabling animals to effectively navigate, procreate, forage for food, hunt for prey, or shelter from predators (reviewed in ). Vision plays a pivotal role in many interactions with the environment and with other living organisms. In many vertebrate species, vision is the most predominant sense for accumulating and perceiving environmental information. In the course of evolution, animals have obtained the capacity to perceive and encode their environment via the development of sensory systems such as touch, olfaction, audition, and vision.
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