Direct memory access transfers to read data from memory are reduced by overlaying data into an immediate data space of a descriptor ring. At this time, a retinal reflex is caused and the luminance in the pupil region becomes high if the eye is a living eye. The seal plate carries a shaft bearing for rotatably supporting a drive shaft having an outboard end connected to an impeller disposed within a pump chamber defined cooperatively by the seal plate and a volute housing mounted thereon.