PPPD, also known as 3PD, is a type of persistent non-vertiginous dizziness whose primary trigger is visual motion hypersensitvity. It is a fundamental disturbance of space and motion, and sometimes referred to as visual vertigo because it is exacerbated by viewing complex visual stimuli.
The visual stimulus doesn’t have to be as complex as the pattern above, which is contained in a marvelous lecture handout available online from a team of three physical therapists. It can be elicited by walking in store or driving, or perhaps even by the eye movements utilized in reading. Of particular note, on p. 43 of the handout, is advice to PTs that if the patient is not responsive to the treatment of oculomotor deficits after 2-4 sessions, a referral to a behavioral optometrist should be made.
3PD can be life changing in a negative way, and its remediation can therefore be life changing in a very positive sense. But these patients are often written off as “head cases”, and don’t receive the benefit of a team approach that takes their debilitating complaints seriously. A chapter reviewing the dilemma of 3PD is contained in a wonderful new book on balance by the science writer Carol Svec, who has a master’s degree in physiological psychology.
After demonstrating how the eyes are the windows to the ears in chapter 3, here are some useful insights into 3PD from the author in Chapter 6:
“Most people don’t realize how much vision contributes to balance. We understand that the vestibular system of the inner ear is the star of our balance system, and we have an intuitive sense of the importance of the body sensations of proprioception – that is, we know how our bodies feel when we are falling and we know where our feet are. We don’t really think about vision. And yet, research has shown that vision can be more than just a second banana when it comes to balance – and it takes up the slack when other systems fail …
But what happens if vision is inaccurate? What if our eyes don’t correctly register movement in the environment or translate the optic flow that helps us navigate through the world? One possible result is a balance problem called persistent postural-perceptual dizziness (PPPD) … Optometrists believe that people with PPPD have difficulty processing visual signals in the brain.”
Svec reviews three general theories about what causes PPPD:
- “Signals to the brain from the visual world may become unreliable if there is something wrong with a person’s vision … In those cases, complex visual scenes or repetitive movements can trigger a kind of motion sickness due to wonky vision creating left-eye/right-eye sensory conflict.”
- “Typically we weight vision as 25 percent of our balance-related information. For some reason, people with PPPD may have developed a personal system that depends on sight more than usual. Perhaps they had an inner-ear disorder when they were young and learned to compensate for vestibular system loss by having vision become more dominant.”
- “The third theory theory suggests that the brains of people with PPD may have difficulty distinguishing and processing central versus peripheral vision cues … Why? Again, no one really knows. Maybe it’s due to a developmental problem that started in infancy, or maybe a concussion or virus affected the brain’s processing centers.”
We discussed the significance of the complexity of visual targets, the visual background, and implications for optic flow with susceptible patients in our series on Eco-Optics. The therapeutic sequence we use is consistent with the idea of habituation, gradually acclimating the patient to progressively more complex stimuli, and gradually introducing movement of the target and movement of the patient. We begin for example with small arc thumb rotations using a blank wall as the background, gradually incorporating wider arcs and gradually introducing a more cluttered environment as the background. We then proceed to more complex targets such as eccentric circles, first with white wall or blue sky as background and go through the same progression.
This is an extremely important progression that must take place if visually hypersensitive patients are to transfer their skills to real world environments.