Vision plays an enormous role in the evolution and survival of many animal species. Roughly two-thirds of all fauna have some form of photonic receptor system.1 is is not unique to animals; plants also have a complex organization of photoreceptor and signaling systems.2,3 However, when most of us think of eyes and vision we tend to think of not only the organs that are capable of sensing light but also specifically those that are capable of forming images.1 Approximately 30% of all fauna have what we would define as image-forming eyes. Even among image-forming eyes, there is a great deal of variety in the performance of biological vision systems. Some, like the primitive eye of the nautilus, are capable only of forming crude images; they are simple collections of photoreceptors and a pinhole opening with only the most basic comparison of light intensity. Our own eyes, in comparison, are extremely complex, sophisticated optical systems capable of forming high-resolution detailed images. Figure 5.1 shows examples of the variety of animal eyes. Vision is extremely integrated into animal behavior. Image-forming vision has played a significant role in the evolution of color displays. It influences both predator and prey behavior and is used for locating food, navigation, and identification of mating suitability. Currently, biological image-capturing photonic systems are attracting a great deal of interest among scientists and technologists due to their sophisticated structure and functionality under severe size and power restrictions. Biological eyes have shown remarkable structural complexity integrating heterogeneous components across many length scales, nanometer through centimeter; the functionality comes from the organization of functional molecules, cells, and larger scale biomaterial-based optical components. ey are

optical powerhouses. e diversity of vision systems found in nature provides a variety of potential synthetic design options with desirable operational properties, particularly compared to conventional designs.4-7 We can find examples of visual systems that offer high visual acuity, some of which are specific to objects in motion (motion hyperacuity) or improved photosensitivity in low-light environments, wide fields of view (FOVs), polarization vision, and improved aberration correction and depth of field. Investigations of biological vision systems have even identified new states of matter.8 Often, these systems have more integrated optical components and come in a significantly more compact package compared to conventional imaging systems. In addition, biological vision systems are composed of a variety of organic materials, offering the potential for extremely compact synthetic systems that ensure high performance, are capable of biological signal amplification, and are biodegradable and biocompatible. ere are many potential applications for technologies that emerge from these inspiring biological systems. Extremely compact cameras are of interest not only for cell phones but also for use in small autonomous and aerospace vehicles, integration into other devices, and prosthetics. ese bioinspired designs may be used to enable new approaches to navigation and sensing and in small systems such as unmanned aerial vehicles (UAVs).5,7,9,10 Biocompatible optics have potential applications in medical systems, such as endoscopes and implantables.11 ey may be used in solar applications such as photovoltaics and thermophotovoltaics to reduce losses and increase efficiency.12 Some other potential applications are in three-dimensional imaging, micro-optical telescopes, and microscopy.10