Cardinal positions and yoke muscles. RSR, right superior rectus; LIO, left inferior oblique; LSR, left superior rectus; RIO, right inferior oblique; RLR, right lateral rectus; LMR, left medial rectus; LLR, left lateral rectus; RMR, right medial rectus; RIR, right inferior rectus; LSO, left superior oblique; LIR, left inferior rectus; RSO, right superior oblique