One of the key findings in BPPV is the presence of nystagmus. This is the medical term for the involuntary eye movement which occurs when the body changes position. It is characterized by alternating smooth pursuit eye movements in one direction and saccadic (quick catch up) movements in the other direction. This is a useful phenomonon as it allows people to keep things in focus even moving and turning your head, without it things would be fuzzy when you nod your head. Nystagmus itself is normal, however there are pathologic forms of nystagmus.
In BPPV there is a phenomenon known as positional nystagmus. When a person with BPPV is in a position which causes them dizziness their eyes exhibit a characteristic motion, called nystagmus. What happens is the inner ear perceives that body is moving (this is the vertigo associated with BPPV) and tells the eyes to move to keep up. The only problem is that the body is not moving, and having your eyes move involuntarily while you are still can be quite disconcerting.
You can see a video of Nystagmus related to BPPV on Youtube.
The maneuver in the video is called “Dix-Hallpike Maneuver” and it elicits the symptoms of BPPV and, more specifically, the nystagmus. There are many types of nystagmus but there are a few qualities of which make the diagnosis of BPPV easier.
Nystagmus associated with BPPV has to have the below characteristics:
- Positional in onset (only in a head hanging position will it come on)
- Short lived (lasts only a few seconds to minutes)
- Geotropic – the top of the eye beats (fast phase) toward the side on which your head is hanging
- Rotatory and small upbeat component – the eye rotates or twists, as above, and has a slight fast phase up motion
- Fatigable – repeating the maneuver again and again will stop it from happening temporarily
- Latent onset – there is a slight lag phase of a few seconds before the nystagmus starts when in the head hanging position.
So why do you get nystagmus with BPPV? Well that can be the subject of another post.