The thicknesses and spheric and aspheric curvatures of the optic components were measured from cross-sections of frozen eyes of C57B1/6J mice. The equivalent refractive index of the crystalline lens was obtained from its back-vertex power in albumin. Refractive indices of the cornea, aqueous and vitreous humors were obtained by refractometry or interferometry at four wavelengths across the visible spectrum. The measurements parallel earlier ones on the hooded rat. The eyes of the mouse and rat differ mainly in size, by a linear scale factor of 1.9-2.0, and only slightly in refractive index. Thus refraction, chromatic aberration, and retinal illumination are easily compared in the two species. An analysis of the contribution of each optical surface to refraction may facilitate extrapolation to other strains of mice. Chromatic aberration is discussed with respect to depth of field and the retinoscopy artefact.