Bielschowsky test is a simple three step test to identify the paretic extra ocular muscle resulting in vertical ocular deviation. The fourth cranial nerve is responsible for controlling the extra ocular muscles and any damage caused to this cranial nerve results in vertical ocular deviation. With fourth cranial nerve palsy, the patient may have vertical and a torsional Diplopia - double vision and hence show an abnormal head posture with the head slightly tilted to the unaffected side with chin depression. Bielschowsky test or Park 3 Step Test provides useful information in assessing the affected muscle in case of ocular deviation.
While conducting Bielschowsky's (head tilt) test, examiner tilts the patient's head in both left and right directions and assesses if it improves or worsens double vision. Tilting the head toward weak or affected muscle will increase image separation and tilting the head toward unaffected muscle will decrease image separation.
First step: The Examiner identifies the hypertropic eye in primary position when the patient is looking in the distance. This implicates depressors of hypertropic eye or elevators of hypotropic eye.
Second step: Ascertains if hypertropia is worse on left gaze or right gaze. Increase on right gaze implicates either the right superior rectus or left superior oblique. Increase on left gaze indicates either a right inferior oblique or left inferior rectus.
Third step: Determines if hypertropia is worse on right head tilt or left head tilt. Increase of the left hypertropia on left head tilt implicates the left superior oblique. Increase of right hypertropia on left head tilt implicates the right inferior rectus. In the fourth cranial palsy, a deviation is better on opposite tilt.
Though Bielschowsky head tilt test is a standard diagnostic tool in isolating the palsied cyclovertical muscle, various other causes of vertical strabismus give rise to positive Bielschowsky head tilt test. Hence this test alone cannot be taken as a sole tool in identifying the fourth cranial palsy.
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Collection of Pages - Last revised Date: September 21, 2020