In ten normal subjects a head tilt of 30° to the same shoulder produced a mean incycloduction of 5° and a head tilt of 30° to the opposite shoulder produced a mean excycloduction of 6.5°. Similar results were obtained when the experiment was performed repeatedly on one eye in the same subject.
Linwong M, Herman SJ. Cycloduction of the Eyes With Head Tilt. Arch Ophthalmol. 1971;85(5):570-573. doi:10.1001/archopht.1971.00990050572008