People with PSP often experience problems with their vision. A very common issue is a paralysis of the eyes which prevents the person from looking downwards. This vertical gaze paralysis makes it hard to do everyday tasks that usually require looking down; such as reading, using an electronic device (e.g., phone, tablet, or computer keyboard), and cutting up food. One solution that is often recommended is to use light-bending prism glasses, shown in the top figure. These glasses bend light from the lower portion of the visual field so the person can see things they cannot look at directly. In principle this seems like an effective solution that should allow people with PSP to retain some of their independence. However, somewhat surprisingly, there is very little scientific evidence that people with PSP benefit from using prisms. Furthermore, very little is known about how and why people use prism glasses, what kind of instruction or training they are given, and what challenges or issues people with PSP experience when trying to use prisms. To try and start answering these question, Dr Ali Lane and I supervised a research project by two masters students (Dan Ford and James Ireland) in which 35 people with PSP were recruited with the help of the PSP Association to tell us about their experiences of using prism glasses.
The majority of participants (74%) had heard of prism glasses, and of these participants 76% had actually tried them. The most common source of information about prisms was a neuro-ophthalmologist (40%), followed by the PSP association (20%), and the most common source of the prisms themselves was an NHS prescription. When we asked about the kinds of things prisms helped people with the most common response was reading (37% of people), followed by eating (24%), using electronic devices (19%), and watching TV (19%). However, when we asked whether people still used the prisms only 20% of people reported persisting with them. This relatively low adherence may be related to the frequency with which people reported experiencing unpleasant side effects such as disorientation (37.5%) and double vision (19%), and practical problems with the weight and fit with existing eyewear. Overall, 43% of people agreed or strongly agreed that the found the prisms useful, but only 18.5% agreed that they liked the prisms.
The results of our survey indicate that while many people with PSP are aware of prism glasses, there is scope to improve patient knowledge of this rehabilitation aid. Furthermore, while some people find them useful for reading, eating, and using electronic devices, most people with PSP do not appear to benefit from prisms or they find them hard to use. Even those who do find them beneficial do not reliably persist with their use. It is likely that better fitting and more systematic training and practice would improve the usefulness of the prisms and reduce the negative impact of side-effects such disorientation. Indeed, there is evidence from stroke survivors with inattention that training improves adherence and outcomes of prism glasses therapy. However, no such training exists for people with PSP.
It is important to be cautious when drawing conclusions from a relatively small sample, but the findings seem to suggest that current approaches to prism therapy for PSP are, unfortunately, relatively ineffective. We believe this is likely due to a lack of reliable training advice for patients, which results from a dearth of scientific evidence about the optimal way to train people in the fitting and use of prisms for different tasks. The only way to resolve this issue is to conduct more evidence-based research that can establish the optimal way to use prism glasses for the rehabilitation of PSP. We are currently looking for ways to fund more research in the important area and would be interested in hearing from people who are considering studying for a PhD on this topic.
You can learn more about our other research into attention and memory in PSP here
s both, as it was Siobhan first experiment and the first time either of us had tried to publish using the Registered Report format. This ended up being a very long processess, and towards the end we had a bit of scare becasue RRs were omitted from the JISC open access deal with Springer, but we got there in the end! The key take-home is that saccadic interference (making irrelvant eye-movements while trying to hold something in memory) causes a highly selective impairment spatial short term memory and does not affect visual short term memory. The novelty of our task was to (a) directly compare spatial and visual STM in the experiment using the same participants and the same task at encoding, but varying the task at recall (in one condition people recalled location, in the other they recalled colour) and (b) to show that, once you control for covert attention, the interference effect in spatial STM is explained by increased guessing. This is important, firstly because it suggests that saccadic interference increases the signal-to-noise of internal spatial maps that represent the memorised locations, rather than reducing the precision of memory representations per se. Secondly, the fact that visual STM was unaffected by saccadic interference is very hard to reconcile with slot models of VSWM. You can read the paper