How is a Park 3-step test for diplopia performed?

Updated: May 21, 2019
  • Author: Jitander Dudee, MD, MA(Cantab), FACS, FRCOphth; Chief Editor: Andrew G Lee, MD  more...
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First, determine which eye appears higher with the head in a normal position. Then, determine which eye is higher with gaze to the left or to the right (ie, with the head turned to the right and then turned to the left). Lastly, determine which eye is higher with the head tilted left and tilted right. (The patient can also help by commenting about when the diplopia is worse.) Then, answer the questions in the following steps:

  • Step 1: Is the left eye or the right eye higher in primary gaze? This reduces the possibilities of muscles from 4 pairs to 2 pairs. For example, if the right eye is higher, the weakness resides either in the muscles depressing the right eye (right superior oblique muscle and right inferior rectus muscle) or in the elevators of the left eye (left superior rectus muscle and left inferior oblique muscle).

  • Step 2: Is the deviation greater with left head turn or with right head turn? This step reduces the alternatives to only one pair of muscles. If the right eye deviates most when the head is turned to the right (both eyes are turning to the left), then only the right superior oblique muscle or the left superior rectus muscle remains.

  • Step 3: Is the deviation greatest with tilting the head to the left or to the right? Called the Bielschowsky head tilt, it relies on the torsional balancing reflexes provoked by head tilt. The higher eye extorts (because of the inferior oblique muscle), while the lower eye intorts (because of the superior oblique muscle).

By combining steps 1-3, only one muscle remains as the culprit. This test requires a logical analysis and the exclusion of alternative possibilities. However, the astute clinician can greatly simplify this process by recognizing that the superior oblique muscle is by far most likely to be responsible for a vertical diplopia. A head tilt to the same side as the involved muscle exacerbates the problem. A very simple rule of thumb is that "the eye that is highest in adduction looks at the affected muscle."

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