Modeling visual fields using virtual ophthalmoscopy: Incorporating geometrical optics, morphometrics, and 3D visualization to validate an interdisciplinary technique.

Visual fields are of particular interest to comparative biologists studying the complex interplay between anatomy, physiology, ecology, and optics. Visual fields have been measured in nearly 100 bird species, and investigators have uncovered associations between quantitative aspects of visual fields and foraging behavior, skull dimensions, and even brain morphology. However, limiting factors including time, access to living subjects, and experimental constraints complicate study of the visual apparatus of rare, endangered, or extinct species. We introduce a modeling technique called virtual ophthalmoscopy (VO) for estimating visual fields of vertebrates. We compare this in-silico technique, which draws on geometrical optics, morphometrics of eyes, and 3D visualization, against experimental data from 12 bird species from behavioral literature. Known values of optical properties, including axial length, lens curvatures, and refractive index, are used to construct and test virtual, schematic eyes in ray-tracing software. Resulting visual fields are measured in 3D-visualization software. These measurements are compared qualitatively and quantitatively with visual fields from the literature. Schematic eyeballs and in-silico visual fields, after iterative improvements using anatomical information from cadaveric specimens, approximate experimental data to the extent of falling within the range of intraspecific variation, suggesting VO is a viable technique for modeling visual fields. Virtual ophthalmoscopy creates an opportunity to expand the sample of species for which visual fields can be quantified and allows new hypotheses regarding the evolution of visual systems to be tested.