Light microscopy and extracellular electrophysiology were used to investigate eye structure and visual physiology of the hyperiid amphipod Scina crassicornis, a mesopelagic species that emits unusually short-wavelength luminescence (λmax=435-444 nm). The overall eye morphology is most similar to some previously described deep-dwelling amphipods, though not other hyperiids. Electroretinograms suggest that S. crassicornis possesses a relatively sensitive eye with slow temporal dynamics, and a monochromatic visual system (λmax=472 nm). Vision in S. crassicornis is well-suited for life in mesopelagic waters, and its short-wavelength luminescence does not play a role in intraspecific sexual signalling.