Fig 8. Primary position and cardinal positions. The pulling power of each of the six extraocular muscles compared to its yoke is assessed by studying the movements of the eyes from the primary position into the cardinal positions. Illustration is arranged as if the patient is facing the examiner. RSR, right superior rectus; LIO, left inferior oblique; RLR, right lateral rectus; LMR, left medial rectus; RIR, right inferior rectus; LSO, left superior oblique; LSR, left superior rectus; RIO, right inferior oblique; LLR, left lateral rectus; RMR, right medial rectus; LIR, left inferior rectus; RSO, right superior oblique.