US Patent 7901072 Prismatic ocular device and personal video display device incorporating same

An ocular device includes a housing, a rotatable ring, a first prism fixed in the rotatable ring, an indexable ring and a second prism fixed in the indexable ring. The housing has a stepped inner profile defining first and second circular tracks in the housing, the tracks being concentric about a rotational axis. The rotatable ring is disposed in the first circular track and is freely rotatable about the rotational axis with respect to the housing. The indexable ring is disposed in the second circular track and is indexable about the rotational axis.