Alexander’s law of nystagmus:
- Fast phase towards heatlhy ear.
- Fast phase magnitude:
– Greatest when looking towards heatlhy ear, decreases when in midline, almost disappers when looking towards impaired ear.
- Complex pathophysiology.
- Simply saying:
– To maintain a fixed gaze direction, you need to have two functioning vestibular components.
– When one is damaged, invariably you will have your eye “slipping” back in the direction of the impaired side.
- If you are looking towards the healthy side, this slow phase in opposite direction of the intended phase alert your brain that your eyes aren’t in the right position. Therefore, it sends signal, causing the corrective fast saccade back to your healthy ear.
- If you are looking towards the damaged side, the intact vestibular system of the contralateral ear can easily “overpower” the impaired side. Therefore, your gaze is fixed at that direction (towards the damaged ear) without slow “slipping” back to the midline.
Alexander’s law is only true in peripheral nystagmus
- There is always only one direction in the nystagmus (direction of fast saccade).
- If the nystagmus is bilateral, it means that the problem is central (normally a posterior circulation problem).