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The Parks–Bielschowsky three-step test, also known as Park's three-step test or Bielschowsky head tilt test,〔 citing von Noorden GK: Binocular vision and ocular motility: Theory and management of strabismus. London, CV Mosby, 2002.〕 is a method used to isolate the paretic extraocular muscle, particularly superior oblique muscle and trochlear nerve (IVth cranial nerve), in acquired vertical double vision. It was originally described by Marshall M. Parks. ==Bielschowsky's head tilt test== *Step 1: Determine which eye is hypertropic in primary position. If there is right hypertropia in primary position, then the depressors of the R eye (IR/SO) or the elevators of the L eye are weak (SR/IO). *Step 2: Determine whether the hypertropia increases on right or left gaze. The vertical rectus muscles have their greatest vertical action when the eye is abducted. The oblique muscles have their greatest vertical action when the eye is adducted. *Step 3: Determine whether the hypertropia increases on right or left head tilt. During right head tilt, the right eye intorts (SO/SR) and the left eye extorts (IO/IR). When a healthy individual tilts their head, the superior oblique and superior rectus muscles of the eye closest to the shoulder keep the eye level. The inferior oblique and inferior rectus muscles keep the other eye level. In patients with superior oblique palsy, the superior rectus muscle’s action is not counteracted by the superior oblique muscles. This leads to vertical deviation of the affected eye when the head is tilted towards the effected eye. However, there is no deviation when the head is tilted towards the unaffected eye because the superior oblique muscle is not stimulated in the effected eye, but rather it is stimulated in the unaffected eye.〔"Head Tilt Test." Head Tilt Test. Orbis Telemedicine, 2003. Web. 08 Dec. 2011. People with superior oblique palsy on one side experience double vision, which is improved or even abolished by tilting the head towards the shoulder on the unaffected side. Tilting the head towards the shoulder on the affected side will make the double vision worse by causing increased separation of the two images seen by the patient. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Parks–Bielschowsky three-step test」の詳細全文を読む スポンサード リンク
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