VISION | Physiological Optics in Fishes

TLDR: The optical system of a typical fish eye, as present in many shallow-water species, is adapted to hydrodynamic constraints and wide-angle color vision, and various fish eyes have fascinating optical adaptations to special visual demands.

Abstract: The optical system of a typical fish eye, as present in many shallow-water species, is adapted to hydrodynamic constraints and wide-angle color vision. The cornea has little refractive power in water, such that the crystalline lens is the dominating refractive element. Fish lenses are gradient-index lenses that often have multiple focal lengths in monochromatic light (multifocal lenses). In light containing a spectrum of wavelengths, a different range of wavelengths is focused on the retina by each focal length, such that well-focused color images are created. Adjustment of focus (accommodation) occurs by movements of the lens in teleosts and chondrichthyes, while it is unclear whether lungfishes and lampreys are capable of accommodation. Various fish eyes have fascinating optical adaptations to special visual demands.