WHEN Alzheimer鈥檚 patients lose their bearings, it may be their vision that is
at fault. Neurologists in New York say patients can鈥檛 interpret the visual cues
we use to work out which direction we are moving in.
Confusion in people with Alzheimer鈥檚 disease is thought to be linked to loss
of memory, so when patients get lost, doctors assume they have forgotten where
they are going. But Charles Duffy of the University of Rochester, who has
studied how monkeys process visual patterns to tell them which way they are
moving, wondered if faulty vision processing also contributed to the
problem.
To test this, he and his colleagues asked 11 people with Alzheimer鈥檚 and 18
healthy subjects to watch patterns on a giant computer screen. The screen showed
dots streaming outwards from a spot, giving the impression that the observer is
moving forward. The team then tested the volunteers鈥� ability to detect these
patterns in the presence of other dots moving randomly.
Advertisement
If 15 per cent of the dots moved radially, the young and elderly healthy
people could pick out the origin of the radial pattern. But the Alzheimer鈥檚
patients needed more than twice as many dots to be moving radially to identify
this (Neurology, vol 52, p 958). 鈥淚n the noise-filled environment of
walking around, they are just not getting the same signal quality,鈥� Duffy
concludes. 鈥淭hey can鈥檛 see where they are going.鈥�
What鈥檚 more, six of the Alzheimer鈥檚 patients in the study had far more
trouble than the other five in interpreting the patterns. The same six people
also had more difficulty answering questions about the route they followed
through the hospital to get to the lab.
Duffy suspects that problems interpreting movement could be an early symptom
of Alzheimer鈥檚 disease. Physicians might be able to use his radial dot test to
diagnose the disease early and begin treatment, he suggests, perhaps preventing
the onset of more serious symptoms.