Keeping an Eye on HD: Can Visual Thinking Skills Help Track Disease Progression?

Although eyesight itself is usually preserved as symptoms progress, Huntington’s disease (HD) can affect visual cognition. This means it can affect how the brain recognizes, understands, and responds to what we see.

A previous HDBuzz article focused on this topic, and now, the same research group has published a new study that builds on those findings. Rather than studying participants at just one time point, the researchers followed them over the course of 2 years! They wanted to better understand how visual cognition evolves as HD progresses, and whether this might help predict changes in movement, thinking or a person’s quality of life down the line. 

Seeing is not the same as understanding

Visual cognition is different from vision. Someone can have clear eyesight and still struggle to make sense of what they are seeing. Vision is about whether the eyes take in information clearly. Visual cognition is about what the brain does with that information.

These skills help us make sense of the world around us, whether we are crossing a road, fishing a phone out from behind the couch, spotting the milk section in a huge supermarket, recognising a friend we have not seen in years, or weaving through a crowded shopping centre. Because these actions usually feel automatic, we may not notice these skills until they start to become harder. In HD, changes in visual cognition may be subtle at first, but they can still affect a person’s confidence and independence.

From a snapshot to a moving picture

A recent study on visual cognition was conducted by a team of researchers led by Juan Carlos Gómez-Esteban. The group’s earlier study was like a still photograph: it compared people at different stages of HD at one point in time. That kind of study is useful because it can show differences between groups. But, as we know, HD progresses differently for each person. A single snapshot cannot fully show how individuals change as the disease moves forward.

The new study was longitudinal, which means the same people were assessed repeatedly over time. This gives researchers more of a moving picture. Instead of only asking, “Are people with HD different from people without HD?”, the researchers could ask, “How do visual cognition skills change over 2 years in people with and without HD?”

The study began with 148 participants: 78 people without HD, 39 people with premanifest HD, and 31 people with early manifestmanifest after HD diagnosis, or when symptoms are already showing HD. Not everyone completed every visit, which is common in longer studies, but the majority completed their follow-up visits after 1 year and 2 years. 

The different parts of visual thinking

Visual cognition is not just one skill; there are many parts to it, and the researchers used different tests and tools to measure it. One aspect is visual attention which means an individual’s ability to focus on the important parts of a visual scene. Imagine standing at an airport trying to find your flight number on the screen. Your eyes may see everything, but your brain has to filter the information and focus on what matters, like your flight number or destination. If visual attention becomes weaker, busy environments may feel more confusing or tiring.

They also measured visual perception and processing speed. Visual perception is the brain’s ability to recognise and interpret objects. Processing speed is how quickly the brain can do this. Slower processing does not mean someone cannot understand what they are seeing. It might just mean they need more time. This skill is important when it comes to activities like reading or reacting to traffic changes. 

Another area was visuospatial ability, which means understanding where things are in space and how they relate to one another. Ever clipped your funny bone on a door or stubbed your toe on the bed? Your visuospatial skills may have briefly abandoned you. These skills are very important to judge distance, parallel park on a busy street  or to reach for a cup without knocking it over.

The study also looked at visual memory, or remembering what we have seen. This might include remembering where you put your keys or recognising faces. This team’s earlier study suggested that visual memory might be one of the first visual thinking skills affected in HD.

Finally, the researchers measured visual executive function. This skill helps us plan, problem-solve, and decide what to do next. In combination with visual information, it helps us complete puzzles or change strategy when something is not working.

What changed over time?

The clearest changes were seen in people with early manifestmanifest after HD diagnosis, or when symptoms are already showing HD, who showed a faster decline in visual attention and visual erception and processing speed than people without HD. This means that over time, people with early HD may find it harder to quickly take in what they are seeing, pick out what matters, and respond to it.

For people with premanifest HD (who carry the gene but do not yet have overt symptoms), the picture was more subtle. As a group, their visual thinking skills did not decline much faster over the 2 years than those of people without HD. There was no big drop across any of the tests.

But one skill stood out: visual memory. This is the ability to remember what we have seen. Visual memory got worse as people moved closer to their estimated age of HD symptom onset. This supports the idea that visual memory may be one of the earlier visual thinking skills affected in HD.

Looking ahead through visual cognition

The researchers then asked another important question: could visual thinking skills at the start of the study give clues about what symptoms might occur later?

The answer was yes.

In people with premanifest HD, lower scores on the visual thinking tests were linked with more movement changes over time. This does not mean that these tests can predict exactly what will happen to one person. But it does suggest  that visual thinking tests may help researchers spot early signs that HD is starting to move forward.

In people with early manifestmanifest after HD diagnosis, or when symptoms are already showing HD, the clues were a little different. Lower scores in visual attention and visuospatial ability at the start of the study were linked with more thinking changes over the next 2 years. Visuospatial ability also gave some clues about later movement changes. 

So, visual thinking may tell researchers different things at different points in HD. Before diagnosis, it may give clues about future movement changes. After early symptoms begin, it may give clues about future thinking changes.

The Big (Moving) Picture

Many HD clinical trials aim to treat people as early as possible, ideally before major symptoms develop. But early HD can be hard to measure. That is why researchers need sensitive tools that can pick up subtle changes early. Visual thinking tests could become one useful part of that toolkit. They would not replace existing HD assessments, but they could add another layer of information alongside movement exams, thinking tests, brain scans, genetic information, and other biomarkers.

There are still reasons to be cautious. This was a relatively small study, especially once participants were divided into premanifest and early HD groups. Some people also missed follow-up visits. Larger and longer studies will still be needed to confirm these findings.

Overall, this study adds another layer to our understanding of HD progression. Visual memory may be especially sensitive before clear movement symptoms begin, while visual attention and visual perception/processing speed may change more quickly once early HD has started. Visual thinking tests may help researchers understand not only what is changing now, but what might change next.

In other words, the “mind’s eye” may offer another way to follow HD over time.

As always, a huge and sincere thank you to everyone who took part in this study and gave their time and commitment over 2 years of research.

Summary

• In early HD, visual attention and visual perception/processing speed declined faster over 2 years. 
• In premanifest HD, visual memory worsened as people got closer to their estimated age of symptom onset. 
• Visual thinking scores helped predict later movement changes in premanifest HD and later thinking changes in early HD.
• Visual thinking tests could offer a new way to follow HD over time and predict what may change next.